CLAIM FOR PRIORITY 
     This application claims priority from PCT International Application Number PCT/US00/14768 (International Publication No. WO00/73905), filed 26 May 2000, which claims priority from U.S. Provisional Application 60/136,637, filed 27 May 1999. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to the field of integrated circuit (IC) testing and burn-in structures and processes, as well as high bandwidth electronic systems. More particularly, the invention relates to improvements in photolithography-patterned spring contacts and enhanced system interconnect assemblies having photolithography-patterned spring contacts for use in the testing or burn-in of integrated circuits and interconnecting a large number of signals between electronic systems or subsystems. 
     BACKGROUND OF THE INVENTION 
     Integrated circuits are typically tested in wafer form (wafer sort) before they are packaged. During wafer sort, integrated circuits are tested one or few at a time, even though there may be hundreds or even hundreds of thousands of the same integrated circuit located on a wafer. The packaged integrated circuits are then tested again, and burned-in, if necessary. 
     Parallel testing on the wafer level has been limited in number and has so far been limited to low pin count devices, due to the difficulty in managing the large number of interconnects, and the limited amount of electronics which can conventionally be placed close to a wafer under test. 
     Attempts have also been made to burn-in ICs while in the wafer form. However, wafer-level burn-in is plagued with multiple problems, such as thermal expansion mismatch between the connector and the silicon wafer under test. Conventional structures, such as large area substrates having a large plurality of fanout traces which are electrically connected to pin or socket connectors, are typically implemented to manage connections between the IC under test, test electronics, and power management electronics. 
     The density of integrated circuits on semiconductor wafers continues to increase, due to semiconductor device scaling, with more gates and memory bits per unit area of silicon. As well, the use of larger semiconductor wafers (e.g. often having a nominal diameter 8 inches or 12 inches) has become common. However, semiconductor test costs have increased on a cost per unit area of silicon basis. Therefore, semiconductor test costs have increased disproportionately over time, to become a greater percentage of the total manufacturing cost for each integrated circuit device. 
     Furthermore, advances in chip scale packaging (CSP) and other forms of small footprint packages have often made traditional packaged IC handlers obsolete for testing and burn-in. 
     In some conventional large surface area substrate integrated circuit (IC) test boards, electrical contacts between the test board and an integrated circuit wafer are typically provided by tungsten needle probes. However, tungsten needle probe technology is not able to meet the interconnect requirements of advanced semiconductors having higher pin counts, smaller pad pitches, and higher clock frequencies. 
     While emerging technologies have provided spring probes for different probing applications, most probes have inherent limitations, such as limited pitch, limited pin count, varying levels of flexibility, limited probe tip geometries, limitations of materials, and high costs of fabrication. 
     K. Banerji, A. Suppelsa, and W. Mullen III, Selectively Releasing Conductive Runner and Substrate Assembly Having Non-Planar Areas, U.S. Pat. No. 5,166,774 (24 Nov. 1992) disclose a runner and substrate assembly which comprises “a plurality of conductive runners adhered to a substrate, a portion of at least some of the conductive runners have non-planar areas with the substrate for selectively releasing the conductive runner from the substrate when subjected to a predetermined stress”. 
     A. Suppelsa, W. Mullen III and G. Urbish, Selectively Releasing Conductive Runner and Substrate Assembly, U.S. Pat. No. 5,280,139 (18 Jan. 1994) disclose a runner and substrate assembly which comprises “a plurality of conductive runners adhered to a substrate, a portion of at least some of the conductive runners have a lower adhesion to the substrate for selectively releasing the conductive runner from the substrate when subjected to a predetermined stress”. 
     D. Pedder, Bare Die Testing, U.S. Pat. No. 5,786,701 (28 Jul. 1998) disclose a testing apparatus for testing integrated circuits (ICs) at the bare die stage, which includes “a testing station at which microbumps of conductive material are located on interconnection trace terminations of a multilayer interconnection structure, these terminations being distributed in a pattern corresponding to the pattern of contact pads on the die to be tested. To facilitate testing of the die before separation from a wafer using the microbumps, the other connections provided to and from the interconnection structure have a low profile”. 
     D. Grabbe, I. Korsunsky and R. Ringler, Surface Mount Electrical Connector, U.S. Pat. No. 5,152,695 (06 Oct. 1992) disclose a connector for electrically connecting a circuit between electronic devices, in which “the connector includes a platform with cantilevered spring arms extending obliquely outwardly therefrom. The spring arms include raised contact surfaces and in one embodiment, the geometry of the arms provide compound wipe during deflection”. 
     H. Iwasaki, H. Matsunaga, and T. Ohkubo, Partly Replaceable Device for Testing a Multi-Contact Integrated Circuit Chip Package, U.S. Pat. No. 5,847,572 (08 Dec. 1998) disclose “a test device for testing an integrated circuit (IC) chip having side edge portions each provided with a set of lead pins. The test device comprises a socket base, contact units each including a contact support member and socket contact numbers, and anisotropic conductive sheet assemblies each including an elastic insulation sheet and conductive members. The anisotropic conductive sheet assemblies are arranged to hold each conductive member in contact with one of the socket contact members of the contact units. The test device further comprises a contact retainer detachably mounted on the socket base to bring the socket contact members into contact with the anisotropic sheet assemblies to establish electrical communication between the socket contact members and the conductive members of the anisotropic conductive sheet assemblies. Each of the contact units can be replaced by a new contact unit if the socket contact members partly become fatigued, thereby making it possible to facilitate the maintenance of the test device. Furthermore, the lead pins of the IC chip can be electrically connected to a test circuit board with the shortest paths formed by part of the socket contact members and the conductive members of the anisotropic conductive sheet assemblies”. 
     W. Berg, Method of Mounting a Substrate Structure to a Circuit Board, U.S. Pat. No. 4,758,9278 (19 Jul. 1988) discloses “a substrate structure having contact pads is mounted to a circuit board which has pads of conductive material exposed at one main face of the board and has registration features which are in predetermined positions relative to the contact pads of the circuit board. The substrate structure is provided with leads which are electrically connected to the contact pads of the substrate structure and project from the substrate structure in cantilever fashion. A registration element has a plate portion and also has registration features which are distributed about the plate portion and are engageable with the registration features of the circuit board, and when so engaged, maintain the registration element against movement parallel to the general plane of the circuit board. The substrate structure is attached to the plate portion of the registration element so that the leads are in predetermined position relative to the registration features of the circuit board, and in this position of the registration element the leads of the substrate structure overlie the contact pads of the circuit board. A clamp member maintains the leads in electrically conductive pressure contact with the contact pads of the circuit board”. 
     D. Sarma, P. Palanisamy, J. Heam and D. Schwarz, Controlled Adhesion Conduct or, U.S. Pat. No. 5,121,298 (09 Jun. 1992) disclose “Compositions useful for printing controllable adhesion conductive patterns on a printed circuit board include finely divided copper powder, a screening agent and a binder. The binder is designed to provide controllable adhesion of the copper layer formed after sintering to the substrate, so that the layer can lift off the substrate in response to thermal stress. Additionally, the binder serves to promote good cohesion between the copper particles to provide good mechanical strength to the copper layer so that it can tolerate lift off without fractured”. 
     R. Mueller, Thin-Film Electrothermal Device, U.S. Pat. No. 4,423,401 (27 Dec. 1983) discloses “A thin film multilayer technology is used to build micro-miniature electromechanical switches having low resistance metal-to-metal contacts and distinct on-off characteristics. The switches, which are electrothermally activated, are fabricated on conventional hybrid circuit substrates using processes compatible with those employed to produce thin-film circuits. In a preferred form, such a switch includes a cantilever actuator member comprising a resiliently bendable strip of a hard insulating material (e.g. silicon nitride) to which a metal (e.g. nickel) heating element is bonded. The free end of the cantilever member carries a metal contact, which is moved onto (or out of) engagement with an underlying fixed contact by controlled bending of the member via electrical current applied to the heating element”. 
     S. Ibrahim and J. Elsner, Multi-Layer Ceramic Package, U.S. Pat. No. 4,320,438 (16 Mar. 1982) disclose “In a multi-layer package, a plurality of ceramic lamina each has a conductive pattern, and there is an internal cavity of the package within which is bonded a chip or a plurality of chips interconnected to form a chip array. The chip or chip array is connected through short wire bonds at varying lamina levels to metallized conductive patterns thereon, each lamina level having a particular conductive pattern. The conductive patterns on the respective lamina layers are interconnected either by tunneled through openings filled with metallized material, or by edge formed metallizations so that the conductive patterns ultimately connect to a number of pads at the undersurface of the ceramic package mounted onto a metalized board. There is achieved a high component density; but because connecting leads are “taggered” or connected at alternating points with wholly different package levels, it is possible to maintain a 10 mil spacing and 10 mil size of the wire bond lands. As a result, there is even greater component density but without interference of wire bonds one with the other, this factor of interference being the previous limiting factor in achieving high component density networks in a multi-layer ceramic package”. 
     F. McQuade, and J. Lander, Probe Assembly for Testing Integrated Circuits, U.S. Pat. No. 5,416,429 (16 May 1995) disclose a probe assembly for testing an integrated circuit, which “includes a probe card of insulating material with a central opening, a rectangular frame with a smaller opening attached to the probe card, four separate probe wings each comprising a flexible laminated member having a conductive ground plane sheet, an adhesive dielectric film adhered to the ground plane, and probe wing traces of spring alloy copper on the dielectric film. Each probe wing has a cantilevered leaf spring portion extending into the central opening and terminates in a group of aligned individual probe fingers provided by respective terminating ends of said probe wing traces. The probe fingers have tips disposed substantially along a straight line and are spaced to correspond to the spacing of respective contact pads along the edge of an IC being tested. Four spring clamps each have a cantilevered portion which contact the leaf spring portion of a respective probe wing, so as to provide an adjustable restraint for one of the leaf spring portions. There are four separate spring clamp adjusting means for separately adjusting the pressure restraints exercised by each of the spring clamps on its respective probe wing. The separate spring clamp adjusting means comprise spring biased platforms each attached to the frame member by three screws and spring washers so that the spring clamps may be moved and oriented in any desired direction to achieve alignment of the position of the probe finger tips on each probe wing”. 
     D. Pedder, Structure for Testing Bare Integrated Circuit Devices, European Patent Application No. EP 0 731 369 A2 (Filed 14 Feb. 1996), U.S. Pat. No. 5,764,070 (09 Jun. 1998) discloses a test probe structure for making connections to a bare IC or a wafer to be tested, which comprises “a multilayer printed circuit probe arm which carries at its tip an MCM-D type substrate having a row of microbumps on its underside to make the required connections. The probe arm is supported at a shallow angle to the surface of the device or wafer, and the MCM-D type substrate is formed with the necessary passive components to interface with the device under test. Four such probe arms may be provided, one on each side of the device under test”. 
     B. Eldridge, G. Grube, I. Khandros, and G. Mathieu, Method of Mounting Resilient Contact Structure to Semiconductor Devices, U.S. Pat. No. 5,829,128 (03 Nov. 1998), Method of Making Temporary Connections Between Electronic Components, U.S. Pat. No. 5,832,601 (10 Nov. 1998), Method of Making Contact Tip Structures, U.S. Pat. No. 5,864,946 (02 Feb. 1999), Mounting Spring Elements on Semiconductor Devices, U.S. Pat. No. 5,884,398 (23 Mar. 1999), Method of Burning-In Semiconductor Devices, U.S. Pat. No. 5,878,486 (09 Mar. 1999), and Method of Exercising Semiconductor Devices, U.S. Pat. No. 5,897,326 (27 Apr. 1999), disclose “Resilient contact structures are mounted directly to bond pads on semiconductor dies, prior to the dies being singulated (separated) from a semiconductor wafer. This enables the semiconductor dies to be exercised (e.g. tested and/or burned-in) by connecting to the semiconductor dies with a circuit board or the like having a plurality of terminals disposed on a surface thereof. Subsequently, the semiconductor dies may be singulated from the semiconductor wafer, whereupon the same resilient contact structures can be used to effect interconnections between the semiconductor dies and other electronic components (such a wiring substrates, semiconductor packages, etc.). 
     Using the alkmetallic composite interconnection elements of the present invention as the resilient contact structures, burn-in can be performed at temperatures of at least 150° C., and can be completed in less than 60 minutes”. While the contact tip structures disclosed by B. Eldridge et al. provide resilient contact structures, the structures are each individually mounted onto bond pads on semiconductor dies, requiring complex and costly fabrication. As well, the contact tip structures are fabricated from wire, which often limits the resulting geometry for the tips of the contacts. Furthermore, such contact tip structures have not been able to meet the needs of small pitch applications (e.g. typically on the order of 50 μm spacing for a peripheral probe card, or on the order of 75 μm spacing for an area array). 
     T. Dozier II, B. Eldridge, G. Grube, I. Khandros, and G. Mathieu, Sockets for Electronic Components and Methods of Connecting to Electronic Components, U.S. Pat. No. 5,772,451 (30 Jun. 1998) disclose “Surface-mount, solder-down sockets permit electronic components such as semiconductor packages to be releaseably mounted to a circuit board. Resilient contact structures extend from a top surface of a support substrate, and solder-ball (or other suitable) contact structures are disposed on a bottom surface of the support substrate. Composite interconnection elements are used as the resilient contact structures disposed atop the support substrate. In any suitable manner, selected ones of the resilient contact structures atop the support substrate are connected, via the support substrate, to corresponding ones of the contact structures on the bottom surface of the support substrate. In an embodiment intended, to receive an LGA-type semiconductor package, pressure contact is made between the resilient contact structures and external connection points of the semiconductor package with a contact force which is generally normal to the top surface of the support substrate. In an embodiment intended to receive a BGA-type semiconductor package, pressure contact is made between the resilient contact structures and external connection points of the semiconductor package with a contact force which is generally parallel to the top surface of the support substrate”. 
     Other emerging technologies have disclosed probe tips on springs which are fabricated in batch mode processes, such as by thin-film or micro electronic mechanical system (MEMS) processes. 
     D. Smith and S. Alimonda, Photolithographically Patterned Spring Contact, U.S. Pat. No. 5,613,861 (25 Mar. 1997), U.S. Pat. No. 5,848,685 (15 Dec. 1998), and International Patent Application No. PCT/US 96/08018 (Filed 30 May 1996), disclose a photolithography patterned spring contact, which is “formed on a substrate and electrically connects contact pads on two devices. The spring contact also compensates for thermal and mechanical variations and other environmental factors. An inherent stress gradient in the spring contact causes a free portion of the spring to bend up and away from the substrate. An anchor portion remains fixed to the substrate and is electrically connected to a first contact pad on the substrate. The spring contact is made of an elastic material and the free portion compliantly contacts a second contact pad, thereby contacting the two contact pads”. While the photolithography patterned springs, as disclosed by Smith et al., are capable of satisfying many IC probing needs, the springs are small, and provide little vertical compliance to handle the planarity compliance needed in the reliable operation of many current IC prober systems. Vertical compliance for many probing systems is typically on the order of 0.004″-0.010″, which often requires the use of tungsten needle probes. 
     The round trip transit time between the a device under test and conventional test equipment is often longer then the stimulus to response times of high speed electronic circuits. It would be advantageous to provide a test interface system which reduces this transit time, by placing high speed test electronics in close proximity of the device under test, while meeting space and cost constraints. Furthermore, it would be advantageous to provide a test interface system which minimizes the cost, complexity, tooling, and turn around time required to change the test structure for the testing of different devices. The development of such a system would constitute a major technological advance. 
     It would be advantageous to provide a test interface system which provides probe contact with many, hundreds, or even hundreds of thousands of pads for one or more devices on a semiconductor wafer, such as for massively parallel testing and/or burn-in applications, wherein the pads may be in close proximity of one another, with a minimum spacing approaching 1 mil or less, while providing a uniform force across all probes over the entire wafer. It would also be advantageous to provide such a test interface system which organizes and manages the interconnections between the device under test and the tester electronics, while maintaining signal integrity and power and ground stability, and assures that no two or more adjacent pads are contacted by a single test probe tip. Furthermore, it would be advantageous to provide such a test structure which preferably provides planarity compliance with the devices under test. The development of such a system would constitute a further technological advance. 
     In addition, it would be advantageous to provide such a test system which preferably provides continuous contact with many, hundreds, or even hundreds of thousands of pads for one or more devices on a semiconductor wafer over a wide temperature range, while providing thermal isolation between the test electronics and the devices under test. As well, it would be advantageous to provide a system for separate thermal control of the test system and of the devices under test. 
     It would also be advantageous to provide a test interface system which may be used to detect power to ground shorts in any die quickly, and to isolate power from a die having a detected power to ground short, before damage is done to the test electronics. In addition, it would be advantageous to provide a test interface structure which can detect that the contacts to many, hundreds, or even hundreds of thousands of pads are reliably made and are each of the contacts are within the contact resistance specification, to assure that the self inductance and self capacitance of each signal line are below values that would adversely affect test signal integrity, and to assure that the mutual inductance and mutual capacitance between pairs of signal lines and between signal lines and power or ground lines are below values that would adversely affect test signal integrity. As well, it would also be advantageous to provide a test interface structure which provides stimulus and response detection and analysis to many, hundreds, or even hundreds of thousands, of die under test in parallel, and which preferably provides diagnostic tests to a failed die, in parallel with the continued testing of all other die. 
     Furthermore, it would be advantageous to provide a large array interface system which can reliably and repeatedly establish contact to many, hundreds, or even hundreds of thousands of pads, without the need to periodically stop and inspect and/or clean the probe interface structure. 
     It would also be advantageous to provide a system for massively parallel interconnections between electrical components, such as between computer systems, which utilize spring probes within the interconnection structure, to provide high pin counts, small pitches, cost-effective fabrication, and customizable spring tips. The development of such a method and apparatus would constitute a major technological advance. 
     SUMMARY OF THE INVENTION 
     Several embodiments of massively parallel interface integrated circuit test assemblies are disclosed, which use one or more substrates to establish connections between one or more integrated circuits on a semiconductor wafer, and use one or more test modules which are electrically connected to the integrated circuits on the semiconductor wafer through the substrates. One or more layers on the intermediate substrates preferably include MEMS and/or thin-film fabricated spring probes. The massively parallel interface assemblies provide tight pad pitch and compliance, and preferably enable the parallel testing or burn-in of multiple ICs. In some preferred embodiments, the massively parallel interface assembly structures include separable standard electrical connector components, which reduces assembly manufacturing cost and manufacturing time. These massively parallel interface structures and assemblies enable high speed testing in wafer form, and allow test electronics to be located in close proximity to the wafer. Preferred embodiments of the massively parallel interface assemblies provide thermal expansion matching to the wafer under test, and provide a thermal path for system electronic. Alternate massively parallel interface structures provide massively parallel connection interfaces, which may be used in a wide variety of circuitry, such as for interconnecting computers in a network, or for interconnecting other electronic circuitry. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a linear array of photolithographically patterned springs, prior to release from a substrate; 
     FIG. 2 is a perspective view of a linear array of photolithographically patterned springs, after release from a substrate; 
     FIG. 3 is a side view of a first, short length photolithographically patterned spring, having a first effective radius and height after the short length spring is released from a substrate; 
     FIG. 4 is a side view of a second, long length photolithographically patterned spring, having a second large effective radius and height after the long length spring is released from a substrate; 
     FIG. 5 is a perspective view of opposing photolithographic springs, having an interleaved spring tip pattern, before the springs are released from a substrate; 
     FIG. 6 is a perspective view of opposing photolithographic springs, having an interleaved spring tip pattern, after the springs are released from a substrate; 
     FIG. 7 is a top view of a first opposing pair of interleaved multiple-point photolithographic spring probes, in contact with a single trace on an integrated circuit device, and a second opposing pair of interleaved multiple-point photolithographic spring probes, in contact with a single pad on the integrated circuit device; 
     FIG. 8 is a plan view of opposing single-point photolithographic spring probes, before the springs are released from a substrate; 
     FIG. 9 is a top view of parallel and opposing single-point photolithographic spring probes, after the springs are released from a substrate, in contact with a single pad on an integrated circuit device; 
     FIG. 10 is a front view of a shoulder-point photolithographic spring probe; 
     FIG. 11 is a partial cross-sectional side view of a shoulder-point photolithographic spring in contact with a trace on an integrated circuit device; 
     FIG. 12 is a perspective view of a multiple shoulder-point photolithographic spring probe; 
     FIG. 13 is a partial cross-sectional view of a multi-layered spring probe substrate providing controlled impedance and integrated components; 
     FIG. 14 is a partial plan view of a substrate, in which a plurality of trace distribution regions are defined on the probe surface of the substrate, between a plurality of spring probes and a plurality of via contacts; 
     FIG. 15 is a partial cutaway assembly view of a massively parallel test assembly having test electronics located in close proximity to the wafer under test; 
     FIG. 16 is a partial perspective view of a massively parallel interconnection assembly; 
     FIG. 17 is a partial expanded cross-sectional view of a massively parallel test assembly having an intermediate system board, which shows staged pitch and distribution across a substrate, a system board, and a flex circuit having a pad matrix; 
     FIG. 18 is an expanded layer plan view of a wafer, a circular substrate, and a rectangular system board; 
     FIG. 19 is an expanded layer plan view of a wafer, a plurality of rectangular substrates, and a rectangular system board; 
     FIG. 20 is a partial cross-sectional view of one embodiment of the flexible circuit structure; 
     FIG. 21 is a partial cross-sectional view of an alternate embodiment of the flexible circuit, which comprises a flex circuit membrane structure; 
     FIG. 22 is a partial perspective view of a flexible membrane circuit structure, wherein a flexible region is defined as an extension of the electronic test card structure; 
     FIG. 23 is a partial perspective view of an alternate flexible circuit structure, wherein a flexible circuit is attached to an electronic test card structure; 
     FIG. 24 is a partial cross-sectional view of one embodiment of a preferred flex circuit region of a test electronics module, in which the flex circuit is wrapped around the power and ground buss structure, and which preferably includes a thermal path across the flex circuit between a power module and a buss bar; 
     FIG. 25 is a partial cross-sectional view of an alternate embodiment of the flex circuit region of a test electronics module, in which a plurality of power modules mounted on the inner surface of a flex circuit are positioned in thermal contact with a plurality of buss bars; 
     FIG. 26 is a partial cross-sectional view of a second alternate embodiment of the flex circuit region of a test electronics module, in which a power module is electrically connected to the outer surface of a flex circuit, and is positioned in thermal contact with a buss bar; 
     FIG. 27 is a perspective view of an alternate embodiment of a test electronics module, in which an integrated module base provides a pad matrix on a first planar region, and in which a power module is electrically connected to the pad matrix and to one or more buss bars, and is positioned in thermal contact with a buss bar; 
     FIG. 28 is a partial cutaway assembly view of an alternate massively parallel test assembly having an intermediate system board, in which flexible spring probes are located on the lower surface of the system board; 
     FIG. 29 is a partial cutaway assembly view of another alternate massively parallel test assembly having an intermediate system board, in which an interposer structure provides electrical connections between the substrate and the system board; 
     FIG. 30 is a partial cutaway assembly view of a basic massively parallel test assembly, in which a substrate having spring probes is directly connected to the test electronics modules; 
     FIG. 31 is a partial expanded cross-sectional view of a basic massively parallel test assembly, which shows staged pitch and distribution across a substrate and a flex circuit having a pad matrix; 
     FIG. 32 is a partial cutaway assembly view of a massively parallel burn-in test assembly, in which burn-in test modules are connected directly to the system board, and in which separate temperature control systems are provided for the wafer under test and for the test electronics modules; 
     FIG. 33 is a first partial expanded cross-sectional view showing massively parallel test assembly and alignment hardware and procedures; 
     FIG. 34 is a second partial expanded cross-sectional view showing massively parallel test assembly and alignment hardware and procedures; 
     FIG. 35 is a partial schematic block diagram of test circuitry for the massively parallel test system; 
     FIG. 36 is a partial cutaway assembly view of a massively parallel interface assembly, in which a plurality of interface modules are connected, through a plurality of probe spring interposers and a system interconnect board structure; 
     FIG. 37 is a partial cutaway assembly view of an alternate massively parallel interface assembly, in which a plurality of interface modules are connected through a system board and a system interconnect board structure; 
     FIG. 38 is a schematic block diagram of connections between a plurality of computer systems, using a massively parallel interface assembly; and 
     FIG. 39 is a schematic block diagram of connections between a plurality of electronic circuits, using a massively parallel interface assembly. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 is a plan view  10  of a linear array  12  of photolithographically patterned springs  14   a - 14   n , prior to release from a substrate  16 . The conductive springs  14   a - 14   n  are typically formed on the substrate layer  16 , by successive layers of deposited metal  17  (e.g. such as layers  17   a ,  17   b  in FIG.  13 ), such as through low and high energy plasma and sputter deposition processes, followed by photolithographic patterning, as is widely known in the semiconductor industry. 
     The successive layers  17  have different inherent levels of stress. The release regions  18  of the substrate  16  are then processed by undercut etching, whereby portions of the spring contacts  14   a - 14   n , which are located over the release regions  18 , are released from the substrate  16  and extend (i.e. bend) away from the substrate  16 , as a result of the inherent stresses between the deposited metallic layers. Fixed regions  15  (FIG. 3, FIG. 4) of the deposited metal traces remain affixed to the substrate  16 , and are typically used for routing (i.e. such as for redistribution or fan-out) from the spring contacts  14   a - 14   n . FIG. 2 is a perspective view  22  of a linear array  12  of photolithographically patterned springs  14   a - 14   n , after release from a substrate  16 . The spring contacts  14   a - 14   n  may be formed in high density arrays, with a fine pitch  20 , currently on the order of 0.001 inch. 
     FIG. 3 is a side view  26   a  of a first photolithographically patterned spring  14  having a short length  28   a , which is formed to define a first effective spring angle  30   a  (which can be from a few degrees to a full circle), spring radius  31   a , and spring height  32   a , after the patterned spring  14  is released from the release region  18   a  of the substrate  16 , away from the planar anchor region  15 . FIG. 4 is a side view  26   b  of a second photolithographically patterned spring  14 , having a long spring length  28   b , which is formed to define a second large effective spring angle  30   b , spring radius  31   b  and spring height  32   b , after the patterned spring  14  is released from the release region  18   b  of the substrate  16 . The effective geometry of the formed spring tips  14  is highly customizable, based upon the intended application. As well, the spring tips are typically flexible, which allows them to be used for many applications. 
     Patterned spring probes  14  are capable of very small spring to spring pitch  20 , which allows multiple spring probes  14  to be used to contact power or ground pads on an integrated circuit device  44  (FIG. 18, FIG.  19 ), thereby improving current carrying capability. As well, for a massively parallel interconnect assembly  78  (e.g.  78   a , FIG. 15) having an array  12  (FIG. 1) of spring probes  14 , multiple spring probes  14  may be used to probe I/O pads  47  on an IC substrate  48  (FIG.  9 ), such as on an integrated circuit device under test (DUT)  44  (FIG. 18, FIG.  19 ). Every spring probe contact  14  to be verified for continuity after engagement of the spring contacts  14  to the wafer  104  under test (FIG.  15 ), thereby ensuring complete electrical contact between a massively parallel interface assembly  78  and a devices  44  on a wafer  104  (FIG.  15 ), before testing procedures begin. 
     Improved Structures for Miniature Springs. FIG. 5 is a first perspective view of opposing photolithographic springs  34   a , 34   b , having an interleaved spring tip pattern, before spring to substrate detachment. FIG. 6 is a perspective view of opposing interleaved photolithographic springs  34   a ,  34   b , after spring to substrate detachment. 
     The interleaved photolithographic springs  34   a ,  34   b  each have a plurality of spring contact points  24 . When spring contacts are used for connection to power or ground traces  46  or pads  47  of an integrated circuit device  44 , the greatest electrical resistance occurs at the point of contact. Therefore, an interleaved spring contact  34 , having a plurality of contact points  24 , inherently lowers the resistance between the spring contact  34  and a trace  46  or pad  47 . As described above, multiple interleaved spring probes  34  may be used for many applications, such as for high quality electrical connections for an integrated circuit device  44 , or for a massively parallel interface assembly  78  (FIG.  15 ), such as for probing an integrated circuit device  44  during testing. 
     FIG. 7 is a top view  42  of opposing interleaved photolithographic spring pairs  34   a , 34   b  in contact with the same traces  46  or pads  47  on an integrated circuit device under test (DUT)  44 . The interleaved spring contact pair  34   a  and  34   b  allows both springs  34   a  and  34   b , each having a plurality of contact points  24 , to contact the same trace  46  or pad  47 . As shown in FIG. 5, when a zig-zag gap  38  is formed between the two springs  34   a , 34   b  on a substrate  16 , multiple tips  24  are established on each spring  34   a , 34   b . Before the interleaved spring probes  34   a , 34   b  are released from the substrate  16 , the interleaved points  24  are located within an overlapping interleave region  36 . When the interleaved spring probes  34   a , 34   b  are released from the substrate  16 , the interleaved spring points  24  remain in close proximity to each other, within a contact region  40 , which is defined between the springs  34   a ,  34   b . The interleaved spring contact pair  34   a  and  34   b  may then be positioned, such that both interleaved spring probes  34   a  and  34   b  contact the same trace  46 , such as for a device under test  44 , providing increased reliability. As well, since each interleaved spring  34   a , 34   b  includes multiple spring points  24 , contact with a trace  46  is increased, while the potential for either overheating or current arcing across the multiple contact points  24  is minimized. 
     FIG. 8 is a top view of parallel and opposing single-point photolithographic springs  14 , before the springs  14  are released from a substrate  16 . As described above for interleaved springs  34   a ,  34   b , parallel springs  14  may also be placed such that the spring tips  24  of multiple springs contact a single trace  46  on a device  44 . As well, opposing spring probes  14  may overlap each other on a substrate  16 , such that upon release from the substrate  16  across a release region  18 , the spring tips  24  are located in close proximity to each other. FIG. 9 is a top view of parallel and opposing parallel single-point photolithographic springs  14 , after the springs  14  are released from the substrate  16 , wherein the parallel and opposing parallel single-point photolithographic springs  14  contact a single pad  47  on an integrated circuit device  44 . 
     FIG. 10 is a front view of a shoulder-point photolithographic spring  50 , having a point  52  extending from a shoulder  54 . FIG. 11 is a partial cross-sectional side view of a shoulder-point photolithographic spring  50 , in contact with a trace  46  on an integrated circuit device. FIG. 12 is a perspective view of a multiple shoulder-point photolithographic spring  50 . Single point spring probes  14  typically provide good physical contact with conductive traces  46  on an integrated circuit device  22 , often by penetrating existing oxide layers on traces  46  or pads  47  by a single, sharp probe tip  24 . However, for semiconductor wafers  104  or integrated circuit devices having thin or relatively soft traces  46  or pads  47 , a single long probe tip  24  may penetrate beyond the depth of the trace  46 , such as into the IC substrate  48 , or into other circuitry. 
     Shoulder-point photolithographic springs  50  therefore include one or more extending points  52 , as well as a shoulder  54 , wherein the points  52  provide desired penetration to provide good electrical contact to traces  46 , while the shoulder  54  prevents the spring  50  from penetrating too deep into a device  44  or wafer  104 . Since the geometry of the spring probes  50  are highly controllable by photolithographic screening and etching processes, the detailed geometry of the shoulder-point photolithographic spring  50  is readily achieved. 
     FIG. 13 shows a partial cross-sectional view of an ultra high frequency spring probe substrate assembly  56 . The substrate  16 , e.g.  16   a , may be electrically insulative, dielectric, or electrically conductive. For embodiments wherein a spring probe  61  and related electrical conductors  60 ,  68 ,  64  on and through the substrate assembly  56  are required to be impedance matched, one or more conductive reference surfaces  58   a , 58   b , 58   c , 58   d  and vias  65   a , 65   b , 65   c  may preferably be added, either within or on the substrate  16 . The substrate assembly  56  may also contain alternating ground reference traces  62   a , 62   b , which are connected to reference planes  58   a , 58   b , 58   c , to effectively provide a shielded coaxial transmission line environment  63 . As well, the impedance control surfaces  58   a , 58   b , 58   c , 58   d  are not limited to the planar surfaces shown in FIG.  13 . 
     An insulating layer  66  may be deposited on a portion the probe spring  61 , such as on the fixed region of the probe spring  61 , up to but not enclosing the tip  24  (FIG.  2 ), as well as on the trace  60 , which connects the spring probe  61  to the via  68 . A conductive layer  58   d  may be deposited on top of the insulating layer  66 , to provide a coaxial, controlled low impedance connection. Alternate layers of conductive materials  58  and dielectric materials  66  can preferably be integrated within the substrate assembly  56 , such as for embodiments which require decoupling capacitors in close proximity to a probe spring  61 . For a substrate  16  which is a conductive material, such as silicon, a thin oxide layer  57  may preferably be deposited between the substrate  16  and a conductive reference plane  58 C, thereby forming a high capacitance structure  59  between the spring probe  61  and the ground planes  58   a  and  58   b . As well, one or more assembled components  69 , such as passive components  69  (e.g. typically capacitors, resistors, and/or inductors), or active component devices  69 , may be located or incorporated on either surface  62   a , 62   b  of the substrate  16 , e.g.  16   a.    
     The fixed portions  15  of the spring probes  61  typically extend a relatively short distance across the substrate  16 . Traces  60  located on the surface of the substrate  16  are electrically connected to the fixed portions  15  of the spring probes  61 , and electrically connect the probe springs  61  to the vias  68 . The traces may be comprised of a different material than the spring probes  61 , and are preferably comprised of metals having high electrical conductivity (e.g. such as copper or gold). 
     FIG. 14 is a partial plan view  72  of a substrate  16 , in which a plurality of distribution fanout traces  60  are defined on the probe surface  62   a  of the substrate  16 , between a plurality of spring probes  61  and a plurality of via contacts  70 . As described above, the spring probes  61 , which are preferably photolithographically formed springs  61 , may currently be formed with a pitch of approximately 0.001 inch. The traces  60  are preferably routed on the probe surface  62   a , to connect to via contact areas  70 , which are preferably laid out in a matrix across the surface of the substrate  16 . In the substrate  16  shown in FIG. 14, the via contact areas  70  are positioned with a probe surface first distribution pitch  74   a , and a probe surface second distribution pitch  74   b.    
     As the size and design of integrated circuit devices  44  becomes increasingly small and complex, the fine pitch  20  (FIG. 2) provided by miniature spring probe tips  61  becomes increasingly important. Furthermore, with the miniaturization of both integrated circuits  44  and the required test assemblies, differences in planarity between one or more integrated circuits  44  located on a wafer  104  and a substrate  16  containing a large number of spring probes  61  becomes critical. 
     As seen in FIG. 14, lower standoffs  75  are preferably provided on the probe surface  62   a  of the substrate  16 , such as to prevent the substrate  16  from damaging a wafer under test  104 , or to set the spring probe tips  24  to operate at an optimal contact angle. The lower standoffs  75  are preferably made of a relatively soft material, such as polyamide, to avoid damage to the semiconductor wafer under test  104 . In addition, to further avoid damage to active circuits  44  in the semiconductor wafer  104 , the standoffs  75  are preferably placed, such that when the massively parallel interface assembly  78  is aligned with a device  44  on a semiconductor wafer  104 , the standoffs  75  are aligned with the saw streets  136  (FIG. 18, FIG. 19) on the semiconductor wafer  104 , where there are no active devices  44  or test structures. Furthermore, the height of the lower standoffs  75  are preferably chosen to limit the maximum compression of the spring probes  61   a - 61   n , thus preventing damage to the spring probes  61   a - 61   n.    
     The substrate  16  also typically includes one or more alignment marks  77  (FIG.  14 ), preferably on the probe surface  62   a , such that the probe surface  62   a  of the substrate  16  may be precisely aligned with a wafer to be tested  104 . 
     Massively Parallel Interface Assemblies for Testing and Burn-In. FIG. 15 is a partial expanded cross-sectional view of a massively parallel test assembly  78   a  having an intermediate system board  82 . FIG. 16 is a partial perspective view  110  of a massively parallel interface assembly  78   a . FIG. 17 is a partial expanded cross-sectional view  120  of a massively parallel test assembly  78   a  having an intermediate system board  82 , which shows staged pitch and distribution across a substrate  16 , a system board  82 , and a flex circuit  90  having a pad matrix  88  (FIG. 15) of electrical connectors  119   a - 119   n . As shown in FIG.  15  and FIG. 17, the interface assembly  78   a  is typically positioned in relation to a semiconductor wafer  104 , having one or more integrated circuits  44 , which are typically separated by saw streets  136  (FIG. 18, FIG.  19 ). 
     The massively parallel interface assembly  78   a  provides electrical interconnections to a substrate  16 , which may contain hundreds of thousands of spring probe tips  61   a - 61   n , while providing adequate mechanical support for the interface assembly  78   a , to work effectively in a typical integrated circuit testing environment. The interface assembly  78   a  is readily used for applications requiring very high pin counts, for tight pitches, or for high frequencies. As well, the interface assembly  78   a  is easily adapted to provide electrical contact for all traces  46  (FIG. 7) and input and output pads  47  (FIG. 7, FIG. 9) for one or more integrated circuit devices under test  44  on a wafer  104 . 
     As seen in FIG. 15, a plurality of electrically conductive spring probe tips  61   a - 61   n  are located on the lower probe surface  62   a  of the substrate  16 , and are typically arranged with a fine spring pitch  20  (FIG. 1, FIG.  17 ), which is typically required to interconnect to specific pads  47  (FIG. 17) on one or more devices under test  44  on a wafer  104 . The spring probe tips  61   a - 61   n  may have a variety of tip geometries, such as single point springs  14 , interleaved springs  34 , or shoulder point springs  50 , and are fabricated on the substrate  16 , typically using thin-film or MEMS processing methods, to achieve low manufacturing cost, well controlled uniformity, very fine pad pitches  20 , and large pin counts. In some embodiments, the flexible connections  64   a - 64   n  are built in compliance to photolithographic springs, such as described above, or as disclosed in either U.S. Pat. No. 5,848,685 or U.S. Pat. No. 5,613,861, which are incorporated herein by reference. The spring probes  61   a - 61   n  on the probe side  62   a  of the substrate  16  mate with pads  47  on each die  44  of the wafer  104 . 
     The fixed trace portions  15 , 60  (FIG. 3, FIG. 14) are then preferably routed to a plurality of metalized vias  68   a - 68   n , which are typically arranged with a substrate distribution pitch  74   a , 74   b , such that the vias  68   a - 68   n  are preferably distributed relatively uniformly across the substrate  16 . Electrically conductive traces  60  are preferably fabricated on one or both sides of the substrate  16 , preferably providing a distribution of the conductive connections  64   a - 64   n  across the connector surface  62   b  of the substrate  16 . 
     The probe tips  61   a - 61   n  are electrically connected to the electrically conductive connections  64   a - 64   n , preferably through metalized vias  68   a - 68   n  within the substrate  16 . Each of the plurality of electrically conductive connections  64   a - 64   n  are then electrically connected to a plurality of conductive pads  84   a - 84   n  on the lower surface  139   a  on a system board  82 . The preferred metallized via electrical connections  68   a - 68   n  (e.g. such as produced by Micro Substrate Corporation, of Tempe, Ariz.) within the substrate  16 , are typically fabricated using standard PTH methods, or extrusion methods, such as by first creating holes in the substrate  16 , using laser or other drilling methods. The holes are then filled or plated with conductive material, such as by plating or by extrusion. After the conductive vias  68   a - 68   n  are formed, they are typically polished back, to provide a flat and smooth surface. Capacitors may preferably be mounted or built into the substrate  16  (FIG.  13 ), providing close proximity de-coupling to the IC wafer  104  under test. 
     The substrate  16  is preferably comprised of silicon, glass, ceramic, ceramic glass, or other suitable substrate material, and preferably has a thermal coefficient of expansion (TCE) which matches the thermal coefficient of expansion (TCE) of the wafer  104 . In some preferred embodiments of the parallel interface assembly  78 , the substrate  16  is relatively thin, such that the substrate  16 , the spring probes  61   a - 61   n , and the preferred flexible connections  64   a - 64   n  provide enhanced planarity compliance to a wafer under test  104 . 
     In an alternate embodiment of the substrate  16 , a starting substrate  16  (e.g. such as a silicon substrate  16 ), is etched, such as by a plasma etching process or a wet anisotropic etching process, to create through holes (i.e. vias) in the substrate  16 , as practiced in the MEMS industry. The substrate  16  may be thinned, such as by atmospheric plasma ion etching, prior to the creation of the through holes, such that fine pitch holes may be defined in the preferred silicon wafer  16 , thereby creating a flexible substrate  16 . The flexible substrate  16  is compliant to the surface of one or more devices under test  44  on a wafer  104 , such as when a pressure differential (as described in reference to FIG. 32) is provided between the probe surface  62   a  and the connector surface  62   b  of the substrate  16 . As described above, the holes are then filled or plated with conductive material, such as by plating or by extrusion. After the conductive vias  68   a - 68   n  are formed, they are typically polished back, to provide a flat and smooth surface. Capacitors may preferably be mounted or built into the substrate  16  (FIG.  13 ), providing close proximity de-coupling to the IC wafer  104  under test. 
     The electrically conductive connections  64   a - 64   n  are located on the upper connector surface  62   b  of the substrate  16 , and are connected to the vias  68   a - 68   n . The electrically conductive connections  64   a - 64   n  are typically arranged with a connection pitch  122  (FIG.  17 ), which may be aligned with the substrate distribution pitch  74   a , 74   b , or may preferably be redistributed on the upper connector surface  62   b  of the substrate  16 . In some preferred embodiments of the substrate  16 , the electrically conductive connections  64   a - 64   n  are preferably distributed relatively uniformly across the substrate  16 . 
     The electrically conductive connections  64   a - 64   n  are preferably arranged within an area array, having an array pitch  122  such as 0.5 mm, 1.00 mm or 1.27 mm, which provides a reasonable density to mate to plated through-holes (PTH)  86   a - 86   n  on the system board  82  (which are typically arranged with a system board pitch  126 ), and allows the distribution of signals on multiple layers within the system board  82 , without resorting to advanced system boards  82  containing blind conductive vias  86   a - 86   n.    
     The electrically conductive connections  64   a - 64   n , which contact conductive pads  84   a - 84   n  on the underside of the system board  82 , maintain electrical connection between the substrate  16  and the system board  82 . The electrically conductive connections  64   a - 64   n  also provide lateral compliance between a substrate  16  and a system board  82  having different thermal coefficients of expansion (e.g. such as for a low TCE substrate  16  and a relatively high TCE system board  82 ). 
     In an alternate embodiment of the massively parallel interface system  78   b  (FIG. 27) the spring probes  64   a - 64   n  on the connector  62   b  side of the substrate  16  mate directly to a pad matrix  88  on the test electronics modules  92   a - 92   k.    
     The electrically conductive connections  64   a - 64   n  are preferably evenly distributed across the upper connector surface  62   b  of the substrate  16 . Similarly, the conductive pads  84   a - 84   n  are preferably evenly distributed across the lower surface  139   a  of the system board  82 . The distributed layout of the electrically conductive connections  64   a - 64   n  and the conductive pads  84   a - 84   n  provides a large connector pitch  122  and associated pad pitch  124  (e.g. typically on the order of 0.020-0.050 inch), whereby relatively large sized conductive pads  84   a - 84   n  and/or electrically conductive connections  64   a - 64   n  may be used. The distributed pitches  122 ,  124  and relatively large connections promote high quality electrical connections between the substrate  16  and the system board  82  over a wide range of operating temperatures, even when the interface assembly  78   a  and wafer  104  are subjected to elevated temperatures, even for a substrate  16  and a system board  82  which are comprised of materials having different thermal coefficients of expansion (TCE). 
     The electrically conductive connections  64   a - 64   n  are connected to the system board  82 , either permanently (e.g. such as by solder or conductive epoxy) or non-permanently (e.g. such as by corresponding metal pads which mate to the tips  24  of flexible spring probes  64   a - 64   n ). 
     In the preferred embodiment of the massively parallel interconnect assembly  78   a  shown in FIG. 15, the plurality of electrically conductive connections  64   a - 64   n  are flexible spring probes  64   a - 64   n . In embodiments of the substrate  16  in which the electrically conductive connections  64   a - 64   n  are flexible electrically connections  64   a - 64   n , the flexible electrically conductive connections  64   a - 64   n  are typically fabricated using a longer spring length  28  and a larger spring angle  30   b  (which can be up to 360 degrees), as compared to the spring probe tips  61   a - 61   n , to provide a compliance of approximately 4-10 mils. In some embodiments, the flexible connections  64   a - 64   n  are typically built in compliance to photolithographic springs, such as described above, or as disclosed in either U.S. Pat. No. 5,848,685 or U.S. Pat. No. 5,613,861, which are incorporated herein by reference. 
     The conductive pads  84   a - 84   n  on the lower surface of the system board  82  are typically arranged with a pad pitch  124  (FIG.  17 ), such that the conductive pads  84   a - 84   n  are aligned with the electrically conductive connections  64   a - 64   n  located on the upper connector surface  62   b  of the substrate  16 . 
     The conductive pads  84   a - 84   n  on the lower surface of the system board  82  are then routed to conductive paths  86   a - 86   n , which are typically arranged with a system board pitch  126 . The electrically conductive connections  128   a - 128   n , which may be arranged within one or more connection regions  132 , are located on the upper surface of the system board  82 , and are routed to the conductive paths  86   a - 86   n . The electrically conductive connections  128   a - 128   n  are typically arranged in within the connection region  132 , with a system board pad matrix pitch  120 , which is typically aligned with the flex circuit pad matrix pitch  134  for each of the test electronics modules  92   a - 92   k.    
     The system board matrix pitch  120  is typically chosen such that the electrically conductive connections  128   a - 128   n  are aligned with the flex circuit electrical connectors  119   a - 119   n  located on the flex circuits  90 , which are typically arranged in a plurality of pad matrices  88  (FIG.  16 ), having a flex circuit pad matrix pitch  134 . 
     The test electronics modules  92   a - 92   k  are a basic building block for most of the embodiments of the massively parallel interface test assemblies  78   a - 78   d . The test electronics modules  92   a - 92   k  are mounted in parallel (e.g. as seen in FIG.  15 ), to form an array of modules  92   a - 92   k , which each provide electronics support to one or more columns  139  (FIG. 18, FIG. 19) on a wafer  104 , or to a portion of a column  139  or die  44 , along which the test electronics modules  92   a - 92   k  are mounted. 
     FIG. 16 is a partial perspective view  110  of a massively parallel interface assembly  78   a , wherein test electronics modules  92  are mounted on a frame  102 . Each of the test electronics modules  92  shown includes a preferred flex circuit  90 , having a pad matrix  88  of electrical contactors  119 , and one or more power control modules  100 . The flex circuit  90  for each of the test electronics modules  92  is mounted on one or more buss bars  98   a - 98   h , and extends downwardly through the frame  102 . The buss bars  98   a - 98   h  are attached to the frame  102 , such as by electrically isolated fasteners  112 , thereby providing a substantially rigid structure. The frame  102  preferably includes test module alignment guides  118 , as well as frame to system alignment pins  114  and means  116  for fastening the frame  102  to a wafer chuck  106  (FIG.  15 ). The assembly  110  may also preferably include other means for holding the test electronics modules  92   a - 92   k , such as a card cage (not shown) located below the frame  102 . 
     The substrate  16  interfaces to a system board  82 , which provides a standard interface to the tester electronics, at a coarser pitch. It also makes the substrate  16  a basic replacement unit, such that only the substrate  16  is typically required to be changed for a new device under test (DUT) design  44 , or if the spring probes  61  need to be replaced. The combined use of standard pitch system boards  82 , with substrates  16  having fanout traces  60  to small pitch spring probes  61   a - 61   n  reduces both the cost and turnaround time for test and burn-in assemblies  78 . 
     The system board  82 , which is typically comprised of ceramic, high density printed wiring board, or glass board, provides a an alignment surface for the substrate  16 . Due to the larger pitch  122 , 124  (FIG. 17) of the connection between the system board  82  and the substrate  16 , this reference can typically be achieved by mechanical means. As well, the system board  82  provides the first level routing interface between the tester electronics modules  92   a - 92   k  and the substrate  16 . Each of the tester electronics modules  92   a - 92   n  are attached to the system board  82 , via a membrane or flex circuit  90 . 
     In the interface assembly  78   a  shown in FIG. 15, the probe tips  61   a - 61   n  are flexible, which inherently provides planarity compliance between the substrate  16  and the semiconductor wafer  104 . As well, the electrically conductive connections  64   a - 64   n , which are also preferably flexible conductive springs  14 ,  34 ,  50 , provide further planarity compliance between the substrate  16  and the semiconductor wafer  104 . The interface assembly  78   a  therefore provides planarity compliance between a substrate  16  and a wafer  104 . As well, the interface assembly  78   a  also accommodates differences in thermal coefficients of expansion (TCE) between the substrate  16  (which is typically comprised of ceramic, ceramic glass, glass, or silicon) and the system board  82  (which is typically comprised of glass epoxy material). 
     The flexible connections  64   a - 64   n  are preferably laid out on a standardized layout pattern, which can match standardized power and ground pad patterns (i.e. assignments) on the system board  82 , thus allowing the same system board  82  to be used for substrates  16  laid out to mate to different integrated circuit devices  44 . As a system board  82  may be adapted to specialized substrates  16 , for the testing of a variety of different devices  44 , the operating cost for a system board  82  is reduced. 
     Lower substrate standoffs  75 , which are typically taller than other features on the substrate  16  (except for the spring tips  61   a - 61   n ), are preferably placed on the lower surface  62   a  of the substrate  16 , preferably to coincide with the saw streets  94  on a semiconductor wafer under test  104 , thereby preventing the wafer under test  104  from crashing into the substrate  16 , and preventing damage to active regions on the semiconductor wafer  104 . 
     Contact between test electronics modules  92   a - 92   k  and the system board  82  are achieved using solder, pressure contact, or spring probes  119 , 128 . The spring probe tips  119 , 128  (FIG. 17) may have a variety of tip geometries, such as single point springs  14 , interleaved springs  34 , or shoulder point springs  50 , and are fabricated on the substrate  16 , typically using thin-film or MEMS processing methods, to achieve low manufacturing cost, well controlled uniformity, very fine pad pitches  20 , and large pin counts. In some embodiments, the flexible connections  119 , 128  are built in compliance to photolithographic springs, such as described above, or as disclosed in either U.S. Pat. No. 5,848,685 or U.S. Pat. No. 5,613,861, which are incorporated herein by reference. 
     The configuration shown in FIG. 15 brings power through the switchable power modules  100 , and input/output signals  148  (FIG. 22, FIG. 23) from the pin electronics card  94  to the system board  82 . This configuration has the advantage of reducing routing congestion in the flex circuit or membrane  90 . 
     The structure of the interface assembly  78   a  provides very short electrical distances between the probe tips  61   a - 61   n  and the controlled impedance environment in the system board  82 , which allows the interface assembly  78   a  to be used for high frequency applications. For embodiments wherein the traces on one or both surfaces  62   a , 62   b  of the substrate  16  are required to be impedance controlled, one or more conductive reference planes may be added within the substrate  16 , either on top of the traces, below the traces, or both above and below the traces. For ultra high-frequency applications, the substrate  16  may contain alternating ground reference traces, which are connected to the one or two reference planes  58   a ,  58   b  (FIG. 13) at regular intervals using vias  65   a , 65   b  (FIG.  13 ), to effectively provide a shielded coaxial transmission line environment  63 . 
     FIG. 18 is an expanded layer plan view of a wafer  104 , a circular substrate  16 , and a rectangular system board  82 . For substrates  16  which are preferably comprised of silicon (which may be preferably chosen to match the thermal coefficient of expansion (TCE) of a wafer  104 ), the silicon substrate  16  may preferably be fabricated by a similar process to that of a wafer  104 , such that the substrate  16  may be fabricated from a circular wafer substrate  16 . 
     FIG. 19 is an expanded layer plan view of a wafer  104 , a plurality of rectangular substrates  16   a ,  16   b ,  16   c  and  16   d , and a rectangular system board  82 . For substrates which are preferably comprised of ceramic materials, the silicon substrate  16  may preferably be fabricated from one or more rectangular ceramic substrates  16   a ,  16   b ,  16   c  and  16   d . Any of the substrates  16 ,  16   a - 16   b  may include a travel limit mechanism, such as one or more upper standoffs  133  located on the connector surface of the substrate  16 , such as to limit perpendicular travel of the substrate in relation to the system board  82 . 
     As seen in FIG.  18  and FIG. 19, devices  44 , each having a plurality of pads  47 , are formed on a wafer  104 , and are typically populated across the wafer  104  by a series of rows  137  and columns  139 , wherein saw streets are located between the rows  137  and columns  139 . As can be seen in the system board  82  in FIG.  18  and FIG. 19, the electrically conductive connections  128   a - 128   n , which are located on the upper surface of the system board  82 , are typically arranged within one or more connection regions  132 , to connect to flex circuit contactors  119  (FIG.  17 ), which are preferably arranged within a similar number of one or more pad matrices  88  (FIG.  16 ). 
     In some preferred embodiments of the massively parallel interface assembly  78 , each of the test electronics modules  92  (e.g.  92   a ) is identical to the other test electronics modules (e.g.  92   b - 92   k ), thereby having an identical number of test componentry (thereby having an identical test capacity). In some embodiments of the massively parallel interface assembly  78 , a similar number of devices  44  is routed to each test electronics modules  92   a - 92   k.    
     In alternate embodiments of the massively parallel interface assembly  78 , a different number of devices  44  may routed to a test electronics module  92  (e.g.  92   a ), such as for outer columns  139  of devices under test  44  on a specific wafer  106 . For a plurality of standardized test electronics modules  92   a - 92   k  having an identical number of test componentry, a test electronics module  92  which has a greater capacity than the number of devices  44  which are connected may still be used, typically through programming the test electronics module  92  to bypass testing for unused test circuitry  94 , or through system control  230 . 
     FIG. 20 is a partial cross-sectional view of one embodiment of the flexible circuit structure  142   a , having a polyamide layer  144   a , and opposing conductive layers  146   a  and  146   b . FIG. 21 is a partial cross-sectional view of an alternate embodiment of the flexible circuit  90 , which comprises a dielectric flex circuit membrane structure  142   b , and opposing conductive layers  146   a  and  146   b . In some embodiments of the flex circuit  90 , the flex circuit membrane structure  142  is inherently flexible. In alternate embodiments of the flex circuit  90 , the flex circuit structure  142  is rigid in regions where one or both conductive layers are substantially located. The controlled removal of the conductive layers  146   a , 146   b  produces controlled flexibility for the flex circuit  90 , while providing regions of formed conductive paths. 
     FIG. 22 is a partial perspective view of a flexible membrane circuit structure, wherein a flexible region  90   a  is defined on the test card structure  94   a . FIG. 23 is a partial perspective view of an alternate flexible circuit structure, wherein a flexible circuit  90   b  is attached to a test card structure  94   b  by attachments  150  (e.g. such as but not limited to fasteners, heat staking, microwelding, or adhesives). 
     The test electronics  94   a , 94   b  populated on each of the test electronics modules  92   a - 92   k  provide stimulus and response detection for one or more devices under test  44 . The test electronics  94   a , 94   b  are built on a high density interconnect (HDI) substrate  142   a , 142   b , or on a standard printed wiring board  94   a , which is connected to the flexible circuit  90 . The test electronic card  94   a , 94   b  is populated with control and response electronics (e.g. such as test electronics  240  in FIG.  35 ). Each test electronics module  92  (e.g.  92   a ) is connected to the backend electronics and computer interface links  96  (e.g. typically by parallel or serial links). Alternatively, the signal pins in the tester electronics modules  92   a - 92   k  can be connected serially, on a daisy chain, to simplify the electrical connections, such as to external test hardware. Test vector and setup information is sent to the pin electronics, from a system computer  202  and control electronics (e.g. such as external pattern generator  246  in FIG.  35 ), through the links  96 . 
     Within each of the test electronics modules  92   a - 92   k , a test electronics card  94 , is connected to the flex circuit/membrane  90 . Test electronics cards  94  may preferably be fabricated as an integral structure with the flexible circuit  90 , such as on an etched thin film substrate, whereby portions of the substrate are etched, to create the flexible membrane circuit  90 . In an alternate embodiment of the test electronics module, a separate test electronics card substrate  94  is connected to a flex circuit, typically by solder, wire bond or connectors. 
     FIG. 24 is a partial cross-sectional view of one embodiment of the flex circuit region  90  of a test electronic module  92 , which preferably includes a thermally conductive pathway  154  across a flex circuit  90  between a power control module  100  and one or more buss bars  98 . Each of the buss bars  98   a - 98   h , which are typically separately electrically connected to a plurality of external power supplies  234   a - 234   h  (FIG.  35 ), are typically electrically isolated from each other by insulators  152 . The insulators  152  may be a separate layer from the buss bars  98   a - 98   h , or may alternately be an electrically insulative layer  152  on the buss bars  98   a - 98   h.    
     FIG. 25 is a partial cross-sectional view of an alternate embodiment of the flex circuit region  90  of a test electronic module  92 , in which one or more power control modules  100   a - 100   h  are mounted on the inner surface of the flex circuit  90 , and are positioned in thermal contact with a plurality of buss bars  98   a - 98   h.    
     FIG. 26 is a partial cross-sectional view of a second alternate embodiment of the flex circuit region  90  of a test electronic module  92 , in which a power control module  100  is electrically connected to the outer surface of a flex circuit  100 . A power control access region  158  is preferably defined through the flex circuit region  90 , whereby the power control module  100  positioned in intimate thermal contact with a buss bar  98  (e.g. such as buss bar  98   b ). 
     One or more power and ground bus bars  98   a - 98   h  are used to distribute power to all the devices under test  44 . Power control modules  100 , typically comprising de-coupling capacitors, switching control circuits and regulators for each device under test  44 , are preferably mounted on the flex circuit  90  as shown in FIG. 24, FIG. 25, or FIG.  26 . 
     While some preferred embodiments of the test electronics modules  92   a - 92   k  include flex circuit structures  90 , the unique interface structure provided by the flex circuit structure  90  may alternately be achieved by other suitable interface designs. FIG. 27 is a perspective view of one alternate embodiment of a test electronics module  92 , in which an integrated module base  157  provides a pad matrix  88  of electrical contacts  119  on a first planar region  158 . One or more power control modules  100  are electrically connected to electrical contacts  119  located the pad matrix, through power control module (PCM) traces  149 , and to one or more buss bars  98   a - 98   h . The power control modules  100  are also preferably positioned in thermal contact with one or more buss bars  98   a - 98   h . Signal traces  148  are also connected to electrical contacts  119  located the pad matrix  88 . The signal traces  148  extend from the first planar region  158  across a second planar region  159 , and are either connected to test electronics  94 , or extend to link  96 . 
     In the various embodiments of the test electronics modules  92 , one or more bus bars  98  provide the power and heat sink paths for the power control modules  100 . Power for devices under test  44  is typically provided through separate rail buss bars  98 , or may alternately share the same rail buss bars  98  with the power control modules  100 . The power rail buss bars  98  also preferably provide mechanical support for the flex circuit  90  and the system board  82  and/or the test electronics cards  94   a - 94   k . In some embodiments of the test electronics modules  92   a - 92   k , the power control module circuits  100  are connected in the serial scan path, to provide individual power and ground control to the devices under test  44 . 
     Alternate Massively Parallel Test Assemblies. FIG. 28 is a partial cutaway assembly view of an alternate massively parallel test assembly  78   b  having an intermediate system board  82 , in which flexible spring probes  160  are located on the lower surface  139   b  (FIG. 17) of the system board  82 . The structure and features of the massively parallel test assembly  78   b  are otherwise identical to the massively parallel test assembly  78   a  shown in FIG.  15 . The system board spring probes  160 , in conjunction with the electrically conductive connections  64   a - 64   n  on the substrate  16 , provide planarity compliance between the system board  82  and the substrate  16 , and provide high quality electrical connections, over a wide range of temperatures. 
     FIG. 29 is a partial cross-sectional view of an alternate interface assembly  78   c , wherein a large grid array (LGA) interposer connector  162  is located between the substrate  16  and the system board  82 . The LGA interposer connector  162  provides a plurality of conductors  164   a - 164   n  between the electrical connections  64   a - 64   n  on the substrate  16  and plurality of conductive pads  84   a - 84   n  on the lower surface of the system board  82 . In one embodiment, the LGA interposer connector  162  is an AMPIFLEX™ connector, manufactured by AMP, Inc., of Harrisburg Pa. In another embodiment, the interposer connector  162  is a GOREMATE™ connector, manufactured by W. L. Gore and Associates, Inc., of Eau Clare, Wis. In another alternate embodiment, a pogo pin interposer  162  is used to connect opposing conductive pads  84   a - 84   n  on the system board  82  to electrical connections  64   a - 64   n  on the substrate  16 . 
     FIG. 30 is a partial cutaway assembly view of a basic massively parallel test assembly  78   d , in which a substrate  16  having spring probes  61   a - 61   n  is directly connected to the test electronics modules  92   a - 92   k . FIG. 31 is a partial expanded cross-sectional view  166  of the basic massively parallel test assembly  78   d , which shows staged pitch and distribution across a substrate  16  and a test electronics module  92  having a pad matrix  88  of electrical contactors  119 . 
     FIG. 32 is a partial cross sectional view  170  of an alternate massively parallel interface assembly  178   e , which shows one embodiment of a basic clamping structure  172 . The interface assembly  178   e  is typically intended for burn-in testing only, whereby test electronics  94  are packaged in small modules  174 . The modules  174  are mounted directly onto the system board  82 , and are preferably used for burn-in testing, which typically requires significantly less test electronics than the test electronics modules  92   a - 92   k  (e.g. such as shown in FIG.  15 ). The clamping structure  172  shown in FIG. 32 may also be used for the wafer level massively parallel interface assemblies  178   a - 178   d.    
     The interposer substrate  16  is preferably fabricated from a thin substrate  16 , such as a 10 mil thick glass plate, whereby the substrate  16  may flex slightly, to conform to the surface of a wafer under test, to accommodate for non-planarity or bowing between the wafer  134  and the interposer substrate  16 . 
     A seal  180  around the periphery of the interposer substrate  16  preferably provides an air-tight chamber  182 . Air pressure is preferably applied between the system board  82  and the interposer substrate  16 . An applied pressure  184  also thermally isolates the DUT wafer  104  from the test electronics  174 , 94 . While DUT wafers  104  are typically required to operate at elevated temperatures during burn-in testing (e.g. such as at 125-160 degrees Celsius), the test electronics  94  should preferably operate at a lower temperature (e.g. such as below 75 degrees Celsius). 
     The wafer chuck  106  preferably includes a wafer thermal control system  192 , which preferably comprises a wafer heating system  194  and/or a wafer cooling system  196 , such as to provide temperature control to the wafer under test  104 . The wafer thermal control system  192  is preferably controlled by a test system temperature controller  188 , which is typically linked  189  to the system controller  232  (FIG.  35 ). 
     The test electronics  174 , 94  are preferably located in one or more cooling chambers  176 . A cooling system  190  is preferably used to control the operating temperature of the test electronics  174 , 94  within the cooling chambers  176 , and is also preferably controlled by the test system temperature controller  188 . 
     A wafer loading vacuum circuit  186 , having vacuum tracks  208  (FIG.  33 ), is preferably built into the wafer chuck  106 , to provide vacuum suction to hold the wafer under test (DUT)  104  in position, and to improve planarity between the substrate connector  16  and the wafer under test  104 . 
     Test System Architecture. The test system consists of an alignment set up, which performs wafer alignment, cooling unit, and tester electronics. The alignment subsystem and cooling units can be built with technology known in the art. 
     System Alignment. FIG. 33 is a first partial expanded cross-sectional view showing massively parallel test assembly  200  and alignment hardware and procedures. The test assembly  200  includes a carrier ring  202 , which preferably includes one or more alignment features, such as alignment pins  206 , whereby the carrier ring  202  may be aligned to a system board  82 . The system board  82  preferably has mating alignment features, such as alignment holes  226  (FIG.  34 ). 
     A substrate  16  is releaseably mounted to a carrier ring  202 , such as by a flexible tape  204  (e.g. such as a ring-shaped KAPTON™ tape), whereby the electrical connections  64   a - 64   n  (e.g. such as seen in FIG. 31) on the connector surface  62   b  of the substrate  16  are aligned to the alignment pins  206 , such that the electrical connections  64   a - 64   n  on the connector surface  62   b  of the substrate  16  may be aligned to the conductive pads  84   a - 84   n  (FIG. 17) on the lower surface of the system board  82 . 
     The wafer chuck  106  preferably includes a wafer loading vacuum circuit  186 , having one or more wafer loading holes  208  on a wafer loading surface  209 . The wafer loading vacuum circuit  186  is connectable to a vacuum source  210 , and may be sealed by wafer loading vacuum circuit valve  212 . A wafer to be tested  104  is placed onto the wafer chuck  106 , and is held in place by a applied vacuum applied through the wafer loading holes  208 . 
     A substrate  16 , mounted on a carrier ring  202 , which is to be mounted to the wafer chuck  106 , is controllably positioned over the wafer  104 , which is held in place by vacuum applied to the wafer chuck  106 . The substrate  16  and the wafer to be tested  104  are then accurately aligned, such as by a lookup/lookdown camera  214  within a modified wafer probe system  216 , whereby the probe springs  61   a - 61   n  on the probe surface  62   a  (FIG. 17) of the substrate  16  are brought into alignment with the die pads  47  on the DUT wafer  104 . Alignment is typically achieved, either by looking at spring tips  24  (FIG.  2 ), or at alignment marks  77  (FIG. 14) printed on the substrate  16 . 
     The wafer chuck  106  also preferably includes a carrier ring vacuum circuit  218 , having one or more carrier ring vacuum holes  220 . The carrier ring vacuum circuit  218  is also connectable to a vacuum source  210 , and may be sealed by carrier ring vacuum circuit valve  222 . Once the substrate  16  and the wafer to be tested  104  are accurately aligned, the lookup/lookdown camera  214  is removed, and the carrier ring  202  is controllably moved onto the wafer chuck  104 , whereby the substrate  16  is accurately positioned over the wafer  16 , such that the probe springs  61   a - 61   n  on the probe surface  62   a  of the substrate  16  contact the die pads  47  on the DUT wafer  104 . The carrier ring  202  is held in place by a vacuum applied through the carrier ring vacuum holes  220 . 
     The wafer loading vacuum circuit valve  212  and the carrier ring vacuum circuit valve  222  are then closed, such that the applied vacuum to the wafer loading vacuum circuit  206  and the carrier ring vacuum circuit  218  is maintained, while the entire test assembly can be handled as a unit, for mounting to the system board  82  and test electronics modules  92   a - 92   k . In alternate embodiments of the wafer loading vacuum circuit  206  and the carrier ring vacuum circuit  218 , a single valve is used to apply a sealable vacuum to both vacuum circuits  206 , 218 . To enhance the vacuum sustaining ability after the vacuum circuit valves  212  and  222  are closed, each circuit  206 , 218  preferably includes a vacuum chamber, which serves to maintain the vacuum level over time. 
     FIG. 34 is a second partial expanded cross-sectional view showing massively parallel test assembly and alignment hardware and procedures  224 , whereby a massively parallel interface test assembly  78  may be assembled into a system which may then be used for wafer testing. As described above, the system board  82  preferably includes a means for alignment  226  to the carrier ring and/or to the wafer chuck  106 , such as alignment holes  226 . The system board  82 , which is mounted to the test electronics modules  92   a - 92   k  and the frame  102 , is then positioned over the carrier ring  202 , such that the alignment pins  206  engage the alignment holes  226 . A means for attachment  228  is then typically provided, such as between the frame  102  and the wafer chuck  106  or the carrier ring  202 , thus completing the assembly structure. 
     While accurate means (e.g. such as optical alignment) is typically used to align the fine pitch probe springs  61   a - 61   n  to the fine pitch pads  47  on the wafer to be tested, the mechanical alignment provided between the carrier ring  202  and the system board  82  (e.g. such as between alignment pins  206  and holes  226 ) is typically sufficient for the distributed electrical connections  64   a - 64   n  and pads  84   a - 84   n , which preferably have larger features, and preferably have coarser pitches  122 , 124 , respectively. As well, the flex circuit pitch  134  on the pad matrix is relatively large (e.g. on the order of 1 mm), making alignment between the test electronics modules  92   a - 92   k  and the system card  82  relatively easy using similar conventional mechanical alignment techniques. 
     Tester Electronics. FIG. 35 is a partial schematic block diagram of test circuitry  230  for the massively parallel interface test systems  78 . The tester electronics  230  consists of but not limited to a control computer  232 , a power subsystem, test electronics modules  92   a - 92   k , DC parametric and measurement systems  236 , 238 , and control electronics. 
     As seen in FIG. 35, a test electronics module  92  is typically connected to a group  264  of one or more devices to be tested  44  on a wafer  104  (e.g. such as but not limited to a column  139  of devices under test  44 ). 
     The test electronics modules  92   a - 92   k  each provide stimulus signals  250  to the device under test (DUT)  44 , monitor the responses  254 , and store the device under test pass over fail information  258  within the tester memory, or transfer the device under test pass or fail information  258  to the system controller  232 . 
     For example, in memory testing, a test electronics module  92  has all the critical functions of a memory tester. This includes the hardware pattern generator  246  to drive the memory devices under test  44  connected to the same test electronics module  92 , in parallel. Response detection and fail detection circuits in the test electronics module  92  records the fail locations for each device under test  44 , as needed. 
     The test electronics modules  92  are preferably software reconfigurable and programmable, making it possible to configure the test electronics modules  92  for a specific DUT design or test function. A built-in self-test (BIST) engine can also be integrated into the test electronics modules  92 , such as to provide additional test features, 
     Each test electronics module  92  also provides analog multiplexing functions, to route the intended DUT pin  47  to the digital test electronics in the test electronics module  92 , or to one or more DC measurement subsystems  238 , which perform analog measurements of the output signals  254 . 
     Sample Test Sequence. After a wafer to be tested  104  loaded, aligned, and engaged, the system controller  232  sends a control signal to all the power control modules  100 , to connect all power and ground pins  47  for a device under test (DUT)  44  to ground, except for a selected pin  47  to be tested, which is controllably connected to the DC parametric unit  236 . The power supplies  234   a - 234   h  are disconnected from the power buses  98   a - 98   h . The power pin integrity of the selected device  44  is then determined, through the DC parametric unit  236 . 
     The DC parametric unit  236 , which is connected to the power rails  98   a - 98   h , via relay or solid state switches  235 , is then programmed, to check for power to ground shorts. The same sequence is repeated for every power pin on every device under test  44 . 
     Similar testing is performed on the DUT input and output pins  47 , through the test electronics card  94 , to determine short circuits and open circuits for a selected device under test  44 . An open connection for a device under test  44  is typically detected by the absence of a parasitic diode in the input and output pins  47  of the device under test  44 , as is commonly practiced in the art. 
     Upon the completion of setup testing, the integrity of the connections and the status of each device pin  47  is determined, in regard to open or short circuits. An excessive number of measured open circuits for one or more devices under test  44  on a wafer  104  may be due to a defective wafer  104 , to system setup, or to one or more defective devices under test  44 . 
     The test circuitry  230  preferably provides diagnostic capabilities, to further diagnose faults. Shorts can be isolated from the power busses  98  and pin test electronics  94 , by scanning the appropriate bit control pattern into the power control module  100  and pin test electronics module  92 . 
     The remaining devices to be tested  44  can then be powered up, and tested in parallel. Short circuit detection and report circuitry is preferably built into each power control module  100 , such that a particular device under test  44  may be disconnected, if a short circuit is developed in the device under test while the device  44  is tested. Other features, such as but not limited to transient device current testing circuitry, may preferably be included within the power control module  100 , such as to provide additional test coverage. 
     Power Pin Testing. The system controller  232  selectively switches on the power connections to one or more devices under test  44 . With the power supplies  234   a - 234   h  turned off (disconnected), a device under test  44  can be tested for open circuits and short circuits, using the DC parametric unit  236 . 
     I/O Pin Testing. Similarly, the input and output pins  47  on a device under test  44  can be tested for leakage, open, shorts, through the system controller  232 . 
     Device Functional Testing. With test results from power pin testing and I/O Pin Testing, for any devices under test  44  which have failed (e.g. due to power), the input and output pins  47  for the failed devices  44  are typically isolated from the tester common resources. The remaining devices under test  44  which have passed power pin testing and I/O pin testing are then powered up, and may then be tested in parallel. 
     Functional Testing. The stimulus unit  248  and pattern generator  246  generate the input pattern  250  to the device under test  44 . The DUT response  254  is captured in the response block  256 , which compares the device under test  44  output with the expected value from the pattern generator  246  or stimulus unit  248 . A pattern generator  246  is commonly used in memory testing, whereas a truth table representing the device stimulus  250  and expected response  254  can be stored in the pattern memory of the stimulus unit  248  for logic device testing. A fail map or log  258  is maintained for each die  44 . While FIG. 35 portrays one embodiment of the functional schematic of the pattern generation and stimulus/response system architecture, other pattern generation and stimulus/response system architectures may suitably be used to meet the testing requirements of a device under test  44 , as is commonly practiced in the art. 
     Alternate Interface Embodiments. FIG. 36 is a partial cutaway assembly view of a massively parallel interface assembly  270   a , in which a plurality of interface modules  272   a - 272   j  are electrically connected to a system interconnect board  286   a . Each of the interface modules  272  (e.g. such as  272   a ) includes a pad matrix  88  of electrical conductors  119 , which are each electrically connected to a probe spring interposer  276 . 
     Each of the probe spring interposer  276  includes lower surface spring probes  280 , electrically connected to upper surface spring probes  284  by vias  282 . As described above, the lower surface spring probes  280 , as well as the upper surface spring probes  284 , may have a variety of tip geometries, such as single point springs  14 , interleaved springs  34 , or shoulder point springs  50 , and are fabricated on the substrate  16 , typically using thin-film or MEMS processing methods, to achieve low manufacturing cost, well controlled uniformity, very fine pad pitches  20 , and large pin counts. In some embodiments, the flexible connections lower surface spring probes  280  and/or the upper surface spring probes  284  are built in compliance to photolithographic springs, such as described above, or as disclosed in either U.S. Pat. No. 5,848,685 or U.S. Pat. No. 5,613,861, which are incorporated herein by reference. 
     The probe spring interposers  276  are provide electrical connections between each of the interface modules  272   a - 272   j  and the system interconnect board  286   a . The system interconnect board  286   a  has upper surface electrical contactors  290 , vias  291 , upper surface interconnection structures  292  and lower surface interconnection structures  292   294 , such that one or more pads one each interface modules  272  may typically be connected together. The system interconnect board  286   a  may also preferably include board electrical componentry, which may be electrically connected to one or more of the interface modules  272 . Each of the interface modules  272  includes links  96  which provide electrical connections to the system interconnect board  286   a , and may also preferably include interface module circuitry  298 . 
     FIG. 37 is a partial cutaway assembly view of an alternate massively parallel interface assembly  270   b , in which a plurality of interface modules  272   a - 272   i  are electrically connected, through a system board interposer  300  to a system interconnect board  286   b , which includes flexible probe spring  64   a - 64   n , as described above. The system board interposer  300  may preferably include interconnection structures  302  and/or board electrical componentry  304 , which may be electrically connected to one or more of the interface modules  272 . 
     The massively parallel interface assemblies  270   a , 270   b  each provide a versatile and robust interface between a plurality of interconnected structures. The massively parallel interface assembly  270   a  may simply be used to provide a robust massively parallel interface (such as to provide complex parallel connections between similar components). In preferred interface embodiments, the massively parallel interface assemblies  270   a , 270   b  may also include module specific electronic circuitry  298 , or shared circuitry  296 . 
     FIG. 38 is a schematic block diagram  306  of connections between a plurality of computer systems  308   a - 308   n , using a massively parallel interface assembly  270 . FIG. 39 is a schematic block diagram  310  of connections between a plurality of electronic circuits  312   a - 312   n , using a massively parallel interface assembly  270 . 
     System Advantages. The massively parallel interface assemblies  78   a - 78   d  provide signal and power interconnections between a test system and a large number of devices  44  located on a wafer  104 , while providing planarity compliance between the wafer  104  and successive assembly layers (e.g. such as substrate  16 , system board  82 , and the pad matrices  88  on the test electronics modules  92   a - 92   k.    
     As well, the massively parallel interface assemblies  78   a - 78   d  provide short electrical paths for the power and input and output signals, between the test electronics modules  92   a - 92   k  and the devices under test  44 , through the combined use of high pitch spring probe tips  61   a - 61   n , layered substrates  16 , 82 , and the vertically packaged test electronics modules  92   a - 92   k , which typically include flex circuits  90 . 
     Furthermore, while the massively parallel interface assemblies  78   a - 78   d  provide short electrical paths for the power and input and output signals, between the test electronics modules  92   a - 92   k  and the devices under test  44  (thereby reducing round trip transit time), the massively parallel interface assemblies  78   a - 78   d  provide thermal isolation between the test electronics  94  and the devices under test  44 , while providing a uniform force across all mating spring probe  61 /pad  47  pairs over the entire wafer  104 , such that the devices under test  44  may be controllably operated over a wide temperature range, while the test electronics modules  92   a - 92   k  provide enhanced heat transfer away from heat sensitive components (e.g. such as through buss bars  98   a - 98   h ), and while preferably providing enhanced test module temperature control. 
     As well, while the devices under test  44  may be controllably operated over a wide temperature range, the massively parallel test interface structure  78   a - 78   c  preferably provides provide signal and power interconnections between a test system and a large number of devices  44  located on a wafer  104 , which are maintained over the temperature range, through the use of suitably sized, coarse pitch  122 , 124  interconnections between substrate  16 and the system board  82  (which maintains electrical contact between the coarse pitch  122 , 124  interconnections  64   a - 64   n  over the temperature range), and through the specified use of a substrate  16  having a similar coefficient of thermal expansion to the wafer under test  104  (which maintains electrical contact between the fine pitch  20  interconnections  61   a - 61   n  over the temperature range). 
     As described above, the massively parallel test interface assemblies  78  may be used to detect power to ground shorts in any die quickly, and to isolate power from a die having a detected power to ground short before damage is done to the test electronics. In addition, the massively parallel test interface assemblies  78  and related test system may be used to detect that the contacts to many, hundreds, or even hundreds of thousands of pads are reliably made and whether each of the contacts are within the contact resistance specification, and to assure that the self inductance and self capacitance of each signal line are below values that would adversely affect test signal integrity. 
     Furthermore, the massively parallel test interface assemblies  78  and related test system can be used to detect whether the mutual inductance and mutual capacitance between pairs of signal lines and between signal lines and power or ground lines are below values that would adversely affect test signal integrity. 
     As well, the massively parallel test interface assemblies  78  provide stimulus and response detection and analysis to many, hundreds, or even thousands, of die under test in parallel, and which preferably provides diagnostic tests to a failed die, in parallel with the continued testing of all other die. 
     In addition, the massively parallel test interface assemblies  78  can reliably and repeatedly establish contact to many, hundreds, or even hundreds of thousands of pads  47 , without the need to periodically stop and inspect and/or clean the probe interface structure  16 . 
     Furthermore, the massively parallel test interface assemblies  78  inherently organize and manage the interconnections between the devices under test  44  and the tester electronics  230 , while maintaining signal integrity and power and ground stability, and assures that no two or more adjacent pads  47  are contacted by a single test probe tip. 
     Although the disclosed massively parallel interface assemblies are described herein in connection with integrated circuit testing, computer networking, and circuit connections, the assemblies and techniques can be implemented with a wide variety devices and circuits, such as interconnections between integrated circuits and substrates within electronic components or devices, burn-in devices and MEMS devices, or any combination thereof, as desired. 
     Accordingly, although the invention has been described in detail with reference to a particular preferred embodiment, persons possessing ordinary skill in the art to which this invention pertains will appreciate that various modifications and enhancements may be made without departing from the spirit and scope of the claims that follow.
Several embodiments of massively parallel interface structures are disclosed, which may be used in a wide variety of permanent or temporary applications, such as for interconnecting integrated circuits (ICs) to test and burn-in equipment, for interconnecting modules within electronic devices, for interconnecting computers and other peripheral devices within a network, or for interconnecting other electronic circuitry. Preferred embodiments of the massively parallel interface structures provide massively parallel intergrated circuit test assemblies. The massively parallel interface structures preferably use one or more substrates to establish connection between one or more integrated circuits on a semiconductor wafer, and one or more test modules. One or more layers on the intermediate substrates preferably include MEMS and/or thin-film fabrication spring probes. The parallel interface assemblies provide tight signal pad pitch and compliance, and preferably enable the parallel testing or burn-in of multiple ICs, using commercial wafer probing equipment. In some preferred embodiments, the parallel interface assembly structures include separable standard electrical connector components, which reduces assembly manufacturing cost and manufacturing time. These structures and assemblies enable high speed testing in wafer form.