embodiments of the present invention will be described in detail below with reference to the drawings . fig1 is an elevation view of the probe card provided with a probe unit substrate according to the present invention . a probe unit substrate 38 is fixed to one side of a wiring substrate 36 , and a reinforcing plate 40 is fixed to the other side of the wiring substrate 36 . the probe unit substrate 38 is equipped with a ceramic substrate 10 and a multilayer wiring division 42 . on the surface of the ceramic substrate 10 is formed the multilayer wiring division 42 made of thin films , on the surface of which are formed a number of probe mounting pads . micro cantilever type probes 22 are fixed to the respective probe mounting pads . fig2 is a side sectional view of a part of the probe unit substrate according to the first embodiment of the present invention . on the ceramic substrate 10 is formed the multilayer wiring division 42 , on which the micro cantilever type probes 22 are fixed . the ceramic substrate 10 corresponds to the electrical insulating substrate in the present invention . the multilayer wiring division 42 consists of the first conductor layer 12 , the first insulating layer 14 , the second conductor layer 16 and the second insulating layer 18 . the first conductor layer 12 includes through - hole junction pads 24 , flatness improvement rings 48 that surround the through - hole junction pads 24 , and a grounding region 26 that further surrounds the flatness improvement rings 48 . the ceramic substrate 10 is formed with through - holes 28 . conductors buried inside the through - holes 28 are connected with the through - hole junction pads 24 respectively . the through - hole junction pad 24 is formed for the purpose of absorbing a positional displacement that might be caused by heat shrinkage of the through - hole conductor in the ceramic substrate 10 . the through - hole junction pad 24 is connected , via the conductor inside the through - hole 28 , to a wiring on the other side of the ceramic substrate 10 . on the other hand , the through - hole junction pad 24 is connected to the second conductor layer 16 . on the surface of the second insulating layer 18 are formed a number of probe mounting pads 20 . on the probe mounting pad 20 is fixed the root of a probe 22 . as the flatness improvement ring 48 exists around the through - hole junction pad 24 , the surface of the first insulating layer 14 never billows near the through - hole junction pad 24 . accordingly , the multilayer wiring division 42 has smaller undulation as a whole , and thus the probe mounting pad 20 on the second insulating layer 18 never undulates . further , the probe mounting pad 20 never slopes but keeps horizontal . therefore , the probes 22 that are fixed to the probe mounting pads 20 have no variation in heights of their tips 30 . fig3 a is a plan view illustrating a pattern near the through - hole junction pad 24 of the first conductor layer 12 ( see fig2 ). the center on the backside of the through - hole junction pad 24 is connected to the through - hole 28 . around the through - hole junction pad 24 is formed the flatness improvement ring 48 with the first clearance 50 therebetween . further , around the flatness improvement ring 48 is formed a grounding region 26 with the second clearance 52 therebetween . the through - hole junction pad 24 corresponds to the first conductor pattern in the present invention , and the grounding region 26 corresponds to the second conductor pattern in the present invention . the flatness improvement ring 48 surrounds the through - hole junction pad 24 with the first clearance 50 therebetween , and further the grounding region 26 surrounds the flatness improvement ring 48 with the second clearance 52 therebetween . the distance d 1 of the first clearance 50 is 25 micrometers for example , and the distance d 2 of the second clearance is 25 micrometers for example . the width of the flatness improvement ring 48 is 520 micrometers for example . as the distances d 1 and d 2 are smaller than the clearance d in the prior art ( see fig1 a ), the surface drop of the first insulating layer 14 ( see fig2 ) near the first clearance 50 and the second clearance 52 is alleviated , so that the surface undulation of the first insulating layer 14 is reduced . now , the risk of short circuit will be described . as shown in fig3 b , it is assumed that a foreign particle 34 gets stuck in the first clearance 50 . since the distance of the first clearance 50 is set small , if the foreign particle 34 gets stuck therein the short circuit might occur between the through - hole junction pad 24 and the flatness improvement ring 48 . the through - hole junction pad 24 , however , never short - circuits with the grounding region 26 because the flatness improvement ring 48 is insulated from the grounding region 26 . much the same is true if the foreign particle gets stuck in the second clearance 52 instead of in the first clearance 50 . nevertheless , if foreign particles get stuck in both of the first clearance 50 and the second clearance 52 , there would be a risk of the short circuit between the through - hole junction pad 24 and the grounding region 26 , a possibility of such a situation being extremely low . accordingly , comparing to the conventional pattern shown in fig1 b , the risk of short circuit is remarkably reduced . fig4 is a side sectional view of a part of the probe unit substrate according to the second embodiment of the present invention . this embodiment has no above - described flatness improvement ring but planarization patterns . the multilayer wiring division 42 in this embodiment consists of the first conductor layer 12 , the first insulating layer 14 , the second conductor layer 16 , the second insulating layer 18 , the third conductor layer 54 , the third insulating layer 56 , the fourth conductor layer 58 , the fourth insulating layer 60 , the fifth conductor layer 62 , and the fifth insulating layer 64 on the surface of the fifth insulating layer 64 are formed a number of probe mounting pads 20 . the first conductor layer 12 includes the through - hole junction pads 24 and the grounding region 26 that surrounds the through - hole junction pads 24 , but has no flatness improvement ring . the second conductor layer 16 , the third conductor layer 54 and the fourth conductor layer 58 are wiring layers . on the other hand , the fifth conductor layer 62 is a grounding layer . the second conductor layer 16 includes planarization patterns 66 and a predetermined conductor pattern 67 . the predetermined conductor pattern 67 corresponds to the third conductor pattern in the present invention . the fourth conductor layer 58 also includes planarization patterns 68 and a predetermined conductor pattern 69 . the predetermined conductor pattern 69 also corresponds to the third conductor pattern in the present invention . the planarization patterns 66 and 68 are located beneath the probe mounting pads 20 . the planar sizes of these planarization patterns 66 and 68 are larger than the planar size of the probe mounting pad 20 . further , the planar size of the lower planarization pattern 66 is larger than the planar size of the upper planarization pattern 68 . namely , comparing these planar sizes , there is a relationship that the probe mounting pad 20 is smaller than the planarization pattern 68 , which is further smaller than the planarization pattern 66 . for example , the probe mounting pad 20 is 120 micrometers square in planar size , the planarization pattern 68 is 150 micrometers square , and the planarization pattern 66 is 180 micrometers square . the planarization patterns 66 and 68 are intended to erase the boundary ( which is the planar boundary between the conductor layer and the insulating layer ) beneath the probe mounting pads 20 . the planarization patterns 66 and 68 reduce , in the vicinity of the planarization patterns 66 and 68 , the surface undulation of the second insulating layer 18 located above the planarization pattern 66 and the surface undulation of the fourth insulating layer 60 located above the planarization pattern 68 . as a result , the surface undulation of the fifth insulating layer 64 is reduced in the vicinity of the probe mounting pads 20 . accordingly , the probe mounting pads 20 never undulate and keep almost horizontal . therefore , the probes 22 , which are fixed to such probe mounting pads 22 , have no variation in heights of their tips 30 . the planarization patterns 66 and 68 are preferably electrically connected with different patterns made of respective identical conductor layers , noting that it does not matter what kind of an electrical potential for the different pattern . fig5 is a side sectional view of a part of the probe unit substrate according to the third embodiment of the present invention . this embodiment is similar to the second embodiment shown in fig4 , but it differs from the second embodiment in the point that the third conductor layer 54 also includes planarization patterns 70 and the fifth conductor layer 62 also includes planarization patterns 72 . these planarization patterns 70 and 72 are also located beneath the probe mounting pads 20 and have the planar sizes larger than the planar size of the probe mounting pads 20 . in the third embodiment , all of the conductor layers 16 , 54 , 58 and 62 ranging from the second conductor layer 16 to the fifth conductor layer 62 include planarization patterns 66 , 70 , 68 and 72 . the planar sizes of these planarization patterns become larger when located lower , that is , there is a relationship in size that the probe mounting pad 20 is smaller than the planarization pattern 72 , which is smaller than the planarization pattern 68 , which is smaller than the planarization pattern 70 , which is smaller than the planarization pattern 66 . for example , the probe mounting pad 20 is 120 micrometers square in planar size , the planarization pattern 72 is 135 micrometers square , the planarization pattern 68 is 150 micrometers square , the planarization pattern 70 is 165 micrometers square , and the planarization pattern 66 is 180 micrometers square . fig6 is a side sectional view of a part of the probe unit substrate according to the fourth embodiment of the present invention . this embodiment is similar to the second embodiment shown in fig4 , but further includes the flatness improvement rings 48 shown in fig2 . namely , in fig6 , the first conductor layer 12 includes the through - hole junction pads 24 , the flatness improvement rings 48 that surround the through - hole junction pads 24 and the grounding region 26 that further surrounds the flatness improvement rings 48 . the second conductor layer 16 includes the planarization patterns 66 , and the fourth conductor layer 58 includes the planarization patterns 68 . this embodiment has advantageously a combination of the planarization effect of the flatness improvement rings 48 and the planarization effect of the planarization patterns 66 and 68 . next , the planar shape of the planarization pattern will be described . fig7 is a fragmentary plan view of the probe card shown in fig1 as viewed from the bottom of fig1 , the probe card being equipped with the probe unit substrate 38 , which has the planarization patterns shown in fig5 . a number of probes 22 are mounted on the surface of the probe unit substrate 38 . imaginary scribe lines 44 for ic chips , which can be measured with the probe card , are shown by dashed lines . the planarization patterns 72 shown in fig5 are formed inside the multilayer wiring division of the probe unit substrate 38 . the probe mounting pads 20 are located above the planarization patterns 72 . the planarization patterns 72 may be prepared one by one for the respective probe mounting pads 20 , but in this embodiment one planarization pattern 72 is prepared for plural probe mounting pads 20 , noting that the one planarization pattern 72 may be associated with any number of the probe mounting pads 20 . fig8 is a fragmentary plan view illustrating a modified planar shape of the planarization pattern . this embodiment differs from the embodiment shown in fig7 in the relationship between the planarization patterns 72 and the probe mounting pads 20 . one planarization pattern 72 is associated with two probe mounting pads 20 . fig9 is a fragmentary plan view illustrating another modified planar shape of the planarization pattern . the uppermost layer of the multilayer wiring division is the fifth insulating layer , and a number of probe mounting pads 20 are formed thereon . on the probe mounting pads 20 are fixed the probes 22 . the fifth conductor layer 62 is located beneath the fifth insulating layer . the fifth conductor layer 62 ( shown by hatching running from upper right to lower left ) is a grounding layer , and includes a grounding region 74 and the planarization patterns 72 , which are located beneath the probe mounting pads 20 . if the conductor layer that is located beneath and close to the probe mounting pads 20 is the grounding layer , the grounding layer may have only a solid pattern , which covers almost all area . in this embodiment , however , in consideration of easiness of repairing a short circuit place as described later , the conductor layer includes the planarization patterns 72 . the planarization patterns 72 are electrically connected with the grounding region 74 , and compose a part of the grounding layer . the probe mounting pads 20 in this embodiment each has an elongate shape , and these probe mounting pads 20 are divided into groups , each group including plural pads . the planarization patterns 72 , each of which may be associated with plural probe mounting pads belonging to one group , are connected to each other via narrow joints 76 . the planarization patterns 72 are further connected to the grounding region 74 via other narrow joints 78 . the widths of the narrow joints 76 and 78 are 50 to 100 micrometers for example . fig1 is a sectional view taken along the line a - a in fig9 . it is assumed that a short circuit place 80 ( see also fig9 ) has occurred for some reason between the probe mounting pad 20 and the planarization pattern 72 . since the planarization pattern 72 is at the ground potential as shown in fig9 , the above - described short circuit unfavorably brings the probe mounting pad 20 to the ground potential , so that the pad 20 can not feed , to the probe 22 , an electrical signal for wafer testing . then , it is necessary to repair the short circuit place 80 . however , a repairing process by cutting the short circuit place per se would raise the risk of irregularity , which may be caused by the repairing process just beneath the probe mounting pad 20 , and thus such a repairing process is not preferable . therefore , in this embodiment , as shown in fig9 , the two joints 76 may be cut at the line b - b and the line c - c . when the joints 76 are cut , any irregularity would not occur just beneath the probe mounting pad 20 . even if any irregularity occurs after the repairing process , it would not affect the flatness of the probe mounting pad 20 .