1. Field of the Invention
The invention relates to an interconnection (contact) element suitable for effecting pressure connections between electronic components and is particularly useful for contacting semiconductor packages or for contacting a semiconductor directly.
2. Description of Related Art
Interconnection or contact elements may be used to connect devices of an electronic component or one electronic component to another electronic component. For example, an interconnection element may be used to connect two circuits of an integrated circuit chip or including an application specific integrated circuit (ASIC). Interconnection elements may also be used to connect the integrated circuit chip to a chip package suitable for mounting on a printed circuit board of a computer or other electronic device. Interconnection elements may further be used to connect the integrated circuit chip to a test device such as a probe card assembly or other printed circuit board (PCB) to test the chip.
Generally, interconnection or contact elements between electronic components can be classified into at least the two broad categories of xe2x80x9crelatively permanentxe2x80x9d and xe2x80x9creadily demountable.xe2x80x9d
An example of a xe2x80x9crelatively permanentxe2x80x9d interconnection element is a wire bond. Once two electronic components are connected to one another by a bonding of an interconnection element to each electronic component, a process of unbending must be used to separate the components. A wire bond interconnection element, such as between an integrated circuit chip or die and inner leads of a chip or package (or inner ends of lead frame fingers) typically utilizes a xe2x80x9crelatively permanentxe2x80x9d interconnection element.
One example of a xe2x80x9creadily demountablexe2x80x9d interconnection element is the interconnection element between rigid pins of one electronic component received by resilient socket elements of another electronic component, for example, a spring-loaded LGA socket or a zero-insertion force socket. A second type of a xe2x80x9creadily demountablexe2x80x9d interconnection element is an interconnection element that itself is resilient or spring-like or mounted in or on a spring or resilient medium. An example of such an interconnection element is a tungsten needle of a probe card component. The interconnection element of a probe card component is typically intended to effect a temporary pressure connection between an electronic component to which the interconnection element is mounted and terminals of a second electronic component, such as a semiconductor device under test.
With regard to spring interconnection elements, generally, a minimum contact force is desired to effect reliable pressure contact to an electronic component (e.g., to terminals of an electronic component). For example, a contact (load) force of approximately 15 grams (including as little as 2 grams or less and as much as 150 grams or more, per terminal) may be desired to effect a reliable electrical pressure connection to a terminal of an electronic component.
A second factor of interest with regard to spring interconnection elements is the shape and metallurgy of the portion of the interconnection element making pressure connection to the terminal of the electronic component. With respect to the tungsten needle as a spring interconnection element, for example, the contact end is limited by the metallurgy of the element (i.e., tungsten) and, as the tungsten needle becomes smaller in diameter, it becomes commensurately more difficult to control or establish a desired shape at the contact end.
In certain instances, spring interconnection elements themselves are not resilient, but rather are supported by a resilient membrane. Membrane probes exemplify this situation, where a plurality of microbumps are disposed on a resilient membrane. Again, the technology required to manufacture such interconnection elements limits the design choices for the shape and metallurgy of the contact portion of the interconnection elements.
Commonly-owned U.S. patent application Ser. No. 08/152,812 filed Nov. 16, 1993 (now U.S. Pat. No. 5,476,211, issued Dec. 19, 1995), and its counterpart commonly-owned co-pending xe2x80x9cdivisionalxe2x80x9d U.S. patent application Ser. No. 08/457,479 filed Jun. 1, 1995, now U.S. Pat. No. 6,049,976, U.S. patent application Ser. No. 08/570,230 now U.S. Pat. No. 5,852,871 and U.S. patent application Ser. No. 09/245,499, filed Feb. 5, 1999 now pending, by Khandros, disclose methods for making spring interconnection elements. In a preferred embodiment, these spring interconnection elements, which are particularly useful for micro-electronic applications, involve mounting an end of a flexible elongate element (e.g., wire xe2x80x9cstemxe2x80x9d or xe2x80x9cskeletonxe2x80x9d) to a terminal on an electronic component, coating the flexible element and adjacent surface of the terminal with a xe2x80x9cshellxe2x80x9d of one or more materials. One of skill in the art can select a combination of thickness, yield strength, and elastic modulus of the flexible element and shell materials to provide satisfactory force-to-deflection characteristics of the resulting spring interconnection elements. Exemplary materials for the core element include gold. Exemplary materials for the coating include nickel and its alloys. The resulting spring interconnection element is suitably used to effect pressure, or demountable, interconnections between two or more electronic components, including semiconductor devices.
Commonly-owned, co-pending U.S. patent application Ser. No. 08/340,144, filed Nov. 15, 1994 now U.S. Pat. No. 5,917,707 and its corresponding PCT patent application Ser. No. PCT/US94/13373, filed Nov. 16, 1994 (WO95/14314, published May 16, 1995), both by Khandros and Mathieu, disclose a number of applications for the aforementioned spring interconnection elements, and also disclose techniques for fabricating tip structures at the ends of the interconnection elements. For example, a plurality of negative projections or holes, which may be in the form of inverted pyramids ending in apexes, are formed in the surface of a sacrificial layer (substrate). These holes are then filled with a contact structure comprising layers of material such as gold or rhodium and nickel. A flexible elongate element is mounted to the resulting tip structure and can be overcoated in the manner described hereinabove. In a final step, the sacrificial substrate is removed. The resulting spring interconnection element has a tip structure having controlled geometry (e.g., a sharp point) at its free end.
Commonly-owned, co-pending U.S. patent application Ser. No. 08/452,255, filed May 26, 1995 now U.S. Pat. No. 6,336,269 and its corresponding PCT patent application Ser. No. PCT/US95/14909, filed Nov. 13, 1995 (WO96/17278, published Jun. 6, 1996), both by Eldridge, Grube, Khandros and Mathieu, disclose additional techniques and metallurgies for fabricating tip structures on sacrificial substrates, as well as techniques for transferring a plurality of interconnection elements mounted thereto, en masse, to terminals of an electronic component.
Commonly-owned, co-pending U.S. patent application Ser. No. 08/788,740, filed Jan. 24, 1997 now U.S. Pat. No. 5,994,152 and its corresponding PCT patent application Ser. No. PCT/US96/08107, filed May 24, 1996 (WO96/37332, published Nov. 28, 1996), both by Eldridge, Khandros and Mathieu, disclose techniques whereby a plurality of tip structures are joined to a corresponding plurality of elongate interconnection elements that are already mounted to an electronic component. Also disclosed are techniques for fabricating xe2x80x9celongatexe2x80x9d tip structures in the form of cantilevers. The cantilever tip structures can be tapered, between one end thereof and an opposite end thereof. The cantilever tip structures are suitable for mounting to already-existing (i.e., previously fabricated) raised interconnection elements extending (e.g., free-standing) from corresponding terminals of an electronic component.
Commonly-owned, co-pending U.S. patent application Ser. No. 08/819,464, filed Mar. 17, 1997, now abandoned, by Eldridge, Khandros and Mathieu, representatively discloses a technique whereby a plurality of elongate interconnection elements having different lengths than one another can be arranged so that their outer ends are disposed at a greater pitch than their inner ends. The inner, xe2x80x9ccontactxe2x80x9d ends may be collinear with one another, for effecting connections to electronic components having terminals disposed along a line, such as a center line of the component.
As electronic components get increasingly smaller and the spacing between terminals on the electronic components get increasingly tighter or the pitch gets increasingly finer, it becomes increasingly more difficult to fabricate interconnections including spring interconnection elements suitable for making electrical connection to terminals of an electronic component. Co-pending and commonly-owned U.S. patent application Ser. No. 08/802,054, titled xe2x80x9cMicroelectronic Contact Structure, and Method of Making Same,xe2x80x9d now pending discloses a method of making spring interconnection elements through lithographic techniques. In one embodiment, that application discloses forming a spring interconnection element (including a spring interconnection element that is a cantilever beam) on a sacrificial substrate and then transferring and mounting the interconnection element to a terminal on an electronic component. In that disclosure, the spring interconnection element is formed in the substrate itself through etching techniques. In co-pending, commonly-owned U.S. patent application Ser. No. 08/852,152, titled xe2x80x9cMicroelectronic Spring Contact Elements,xe2x80x9d now U.S. Pat. No. 6,184,053 spring interconnection elements are formed on a substrate, including a substrate that is an electronic component, by depositing and patterning a plurality of masking layers to form an opening corresponding to a shape embodied for the spring interconnection element, depositing conductive material in the opening made by the patterned masking layers, and removing the masking layer to form the free-standing spring interconnection element.
Co-pending and commonly-owned U.S. patent application Ser. No. 09/023,859, titled xe2x80x9cMicroelectronic Contact Structures and Methods of Making Same,xe2x80x9d now pending describes an interconnection element having a base end portion (post component), a body portion (beam component) and a contact end portion (tip component) and methods separately forming each portion and joining the post portion together as desired on an electronic component.
Co-pending and commonly-owned U.S. patent application Ser. No. 09/107,924 now pending and its parent, U.S. Pat. No. 5,772,451 issued Jun. 30, 1998, both entitled xe2x80x9cSockets for Electronic Components and Methods of Connecting to Electronic Components,xe2x80x9d show a socketing device for mating to a packaged semiconductor.
What is needed is a method of fabricating interconnection elements suitable for present fine-pitch electrical connections that is scalable for future technologies. Also needed are improved methods of making interconnection elements, particularly methods that are repeatable, consistent, and inexpensive.
In one aspect, the method comprises successively fabricating a multi-tiered structure to form a compact, resilient interconnect structure. Fabricating each tier or layer involves, in one instance, patterning a plurality of layers of masking material over a substrate. A resilient element is formed and deposited after patterning and cleaned as needed and prepared for a subsequent layer. The method forms, in one embodiment, an interconnection element coupled to the substrate having a body of a plurality of resilient elements, a first resilient element with a first contact region and a second contact region and a first securing region, and a second resilient element with a third contact region coupled to the first resilient element through respective securing regions.
A second aspect of the method of forming a contact element comprises successively alternately patterning a plurality of masking layers and interconnection material layers over an attachment element of an interconnection element coupled to a substrate, the alternately patterned layers defining a body coupled to the attachment element, having a plurality of resilient elements, a portion of adjacent resilient elements separated by a masking layer, and removing the masking layers to form an interconnection element extending from the surface of the substrate.
By forming a body of the interconnection element with a plurality of resilient elements, the mechanical properties of the interconnection element are improved over single beam spring interconnection elements, particularly in sub-micron pitch spacing range of current and future technologies of contact pads or terminals of an integrated circuit. For example, the multiple-leaf portion body of the interconnection element of the invention can achieve improved mechanical properties such as spring constant, compliance, and lower material stress over single beam spring interconnection elements in fine-pitch applications.
The interconnection elements formed by the different aspects of the method of the invention are suitable for making either temporary or permanent electrical connection between contact pads or terminals of an electronic component such as a PCB and a chip under test. In this regard, a method of making electrical connections is disclosed. In one aspect, the method comprises patterning a plurality of interconnection elements on the surface of a first substrate, each interconnection element having an attachment element coupled to a first substrate and a body comprising a plurality of resilient elements, the attachment element coupled to a first surface of the body, a second surface of the body having a contact region capable of contacting a terminal of a chip-scale device. The first substrate is brought together with a second substrate so that the contact regions of the interconnection elements are in contact with the second substrate. For making temporary connection, the first substrate is brought together with another substrate, such as an electronic component, where the contact regions of the second substrate are electrical contacts such as terminals. The interconnection elements react resiliently to maintain contact pressure and, in one embodiment, to maintain an electrical connection between the two components. For making permanent connection, the first substrate is brought together with the second substrate and the contact regions of the interconnection elements are joined or bonded, such as by soldering, welding, or brazing or with a conductive adhesive, to, for example, a terminal of the other substrate. In one embodiment, the interconnection elements are compliant and may accommodate differential thermal expansion between the two substrates.
Disposed on an electronic component, the interconnection elements are particularly suitable for electrical connection with a second electronic components having xe2x80x9cfine-pitchxe2x80x9d contact pads or terminals, for example, spacing of at least less than 5 mils (130 xcexcm), such as 2.5 mils (65 xcexcm). As will be evident from the description that follows, minimized pitch between interconnection elements of an electronic component of the invention is achieved in part by modifying the thickness of the body or spring portion of the interconnection element of the electronic component. Instead of a single beam body, the interconnection elements of the electronic component are comprised of a plurality of resilient elements to improve the mechanical properties of each interconnection element. A desired spring constant of multiple, coordinated springs reinforce and support the primary spring and interconnection element (e.g., tip). A leaf portion body also improves the compliance of the body at a reduced material stress. Applications to larger scale devices, including, for example, devices with contact pitches of about 50-100 mil (1.3-2.6 mm) and even larger are feasible as well.
Other embodiments, features, and advantages of the invention will become apparent in light of the following description thereof.