Abstract:
A ceramic substrate has, on its surface, a multilayer wiring division, on which micro cantilever type probes are fixed. The multilayer wiring division has the first conductor layer, which includes through-hole junction pads, flatness improvement rings surrounding the through-hole junction pads and a grounding region further surrounding the flatness improvement rings. Since the flatness improvement rings are located around the through-hole junction pads, the surface of the first insulating layer, which is located above the first conductor layer, is free from severe undulation even near the through-hole junction pads. Accordingly, the multilayer wiring division has less irregularity in shape as a whole, and thus the probe mounting pads on the surface of the second insulating layer do not slope but keep almost horizontal. The probe unit substrate according to the invention has an advantage of less surface undulation and having non-sloping probe mounting pads without using a complicated manufacturing process.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application is a Divisional Application of U.S. application Ser. No. 12/005,488 filed Dec. 27, 2007 now U.S. Pat. No. 7,504,843, which is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to a probe unit substrate having a feature of planarization or leveling of probe mounting pads. 
   In this specification, the phrase “probe unit” signifies a unit having plural probes for testing electronic parts or electrical parts, and thus it corresponds to, for example, a probe card used for testing an electrical circuit on a semiconductor wafer or a probe unit used for testing a liquid crystal display. Further, the phrase “probe unit substrate” signifies a substrate for the probe unit, which has an internal wiring and is possible to support plural probes. 
     FIG. 11  is an enlarged sectional view illustrating a part of a conventional probe unit substrate. A ceramic substrate  10  has a surface, on which the first conductor layer  12  is formed in a predetermined pattern. Above the first conductor layer  12  are formed the first insulating layer  14 , the second conductor layer  16 , and the second insulating layer  18  in order. On the surface of the second insulating layer  18  are formed a number of probe mounting pads  20 . Micro cantilever type probes  22  are fixed to the respective probe mounting pads  20 . The first conductor layer  12  is formed to be a predetermined pattern, and includes through-hole Junction pads  24  and a grounding region  26 . The ceramic substrate  10  is formed with through-holes  28 , and inner conductors of the through-holes  28  are connected with the through-hole junction pads  24 . The through-hole junction pad  24  is prepared for the purpose of absorbing a positional displacement, which might be caused by thermal contraction of the through-hole conductor of the ceramic substrate  10 . The through-hole junction pads  24  are connected to the second conductor layer  16 . 
   A clearance between the through-hole junction pad  24  and a grounding region  26  is filled with the first insulating layer  14  deposited therein. Accordingly, the surface of the first insulating layer  14  becomes not flat but shows undulation. Such undulation spreads to the second conductor layer  16  and the second insulating layer  18 . Besides, if the second conductor layer  16  is formed in a predetermined pattern, other undulation resulting from the pattern is also added. As a result, undulation appears on the surface of the second insulating layer  18 . If the probe mounting pad  20  rests on such an uneven surface of the second insulating layer  18 , the surface of the probe mounting pad  20  would be in danger of being non-flat or being inclined from the horizontal condition even with flatness. Further, if the micro cantilever type probes  22  are fixed to the respective such probe mounting pads  20 , it could lead to variation in heights of tips  30  of a number of probes  22 . 
   The surface undulation of the first insulating layer  14  will be alleviated if the clearance between the through-hole junction pad  24  and the grounding region  26  is reduced. However, there is a restriction in reduction of the clearance, as will be described below.  FIG. 12A  is a plan view illustrating a pattern of the first conductor layer  12  around the through-hole junction pad  24 . The clearance  32  (a space having no conductor layer) is formed around the through-hole junction pad  24 , and thus the through-hole junction pad  24  is separated from the grounding region  26  with a distance d. The distance d is a hundred micrometers, for example. 
   Since the surface undulation of the first insulating layer  14  is caused by existence of the clearance  32 , it would be possible to alleviate such undulation if the distance d is reduced. That is, as shown in  FIG. 12B , it might be possible to reduce the distance d down to twenty-five micrometers for example. However, if the distance d is reduced, another problem occurs as described below. As shown in  FIG. 12C , when a foreign particle  34  gets stuck in the clearance  32 , there is a risk of short circuit between the through-hole junction pad  24  and the grounding region  26 . Therefore, it is not very preferable to reduce the distance d. Much the same is true in the case of short circuit caused by any wrong pattern instead of the foreign particle  34 . 
     FIG. 13  is a sectional view illustrating in a magnified form a part of another structure of the conventional probe unit substrate. In this probe unit substrate, a multilayer wiring division  42  is composed 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 . This conventional structure brings, as well as the conventional structure as shown in  FIG. 11 , irregularity to the surface of the first insulating layer  14  caused by the fact that the first insulating layer  14  is deposited in the clearance between the through-hole junction pad  24  and the grounding region  26 . In addition, for example, the wiring patterns formed in the second conductor layer  16  and the fourth conductor layer  58  bring the irregularity to the surfaces of the insulating layers  18  and  60  disposed above the conductor layers  16  and  58 . These irregularities spill over into the uppermost surface of the fifth insulating layer  64  so that the surfaces of the probe mounting pads  20  would not be flat or would be inclined from the horizontal condition no matter how flat the surface is. 
   By the way, the technique regarding planarization of a multilayer wiring substrate is known as described below. Concerning the technique for fixing a probe to a conductor layer (which corresponds to the probe mounting pad) formed on the uppermost layer of the multilayer wiring substrate, an improvement in the surface flatness of the multilayer wiring substrate is disclosed in Japanese Patent Publication No. 2006-210473 A (the first publication). 
   In the first publication, a covering resin layer having through-holes is formed on an insulating base, and the through-holes are filled with conductor layers. Accordingly, the height of the surface of the covering resin layer is almost the same as the heights of the surfaces of the conductor layers, resulting in no irregularity. Then, an insulating resin layer and a wiring conductor layer can be formed above a combination of the above-described covering resin layer and the conductor layers. Accordingly, the surface irregularity of the multilayer wiring substrate is alleviated, and a conductor layer is formed on the surface of the multilayer wiring substrate and a number of probes are fixed to the conductor layer without variation in heights of the tips of the probes. 
   According to the above-described technique disclosed in the first publication, the surface irregularity of the multilayer wiring substrate is reduced, but the manufacturing process will be complicated to form “a covering resin layer having through-holes”. According to the first publication, formation of the through-hole in the covering resin layer requires 1) oxygen plasma treatment on the top side of the covering resin layer with the use of a metal layer as a mask, or 2) laser processing for removing a part of the covering resin layer to form through-holes. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a probe unit substrate in which the surface irregularity is alleviated without a complicated manufacturing process so that the probe mounting pads neither undulate nor slope. The probe unit substrate according to the present invention is characterized in formation of flatness improvement rings or planarization patterns in the multilayer wiring division so that the probe mounting pads keep the flat and horizontal conditions. The probe unit substrate according to the first aspect of the present invention has flatness improvement rings, and thus comprises: (a) an electrical insulating substrate having a surface; (b) a first conductor layer formed on the surface of the substrate, the first conductor layer including: first conductor patterns; flatness improvement rings surrounding the first conductor patterns with first clearances therebetween; and a second conductor pattern surrounding the flatness improvement rings with second clearances therebetween; (c) a first insulating layer covering over the first conductor layer; (d) at least one other conductor layer formed above the first insulating layer, and at least one other insulating layer covering over the other conductor layer; and (e) probe mounting pads formed on a surface of an uppermost insulating layer of the at least one other insulating layer. 
   It should be noted, in the present specification, that the words “above” and “beneath” signify the directions described below. The word “above” signifies a direction from the electrical insulating substrate toward the probe mounting pads, and the word “beneath” signifies the opposite direction. Therefore, the words “above” and “beneath” have no connection to the posture of the probe unit substrate and its components against the gravity. 
   The probe unit substrate according to the second aspect of the present invention has planarization patterns, and thus comprises: (a) an electrical insulating substrate having a surface; (b) a first conductor layer formed on the surface of the substrate; (c) a first insulating layer covering over the first conductor layer; (d) at least one other conductor layer formed above the first insulating layer, and at least one other insulating layer covering over the other conductor layer; and (e) probe mounting pads formed on a surface of an uppermost insulating layer of the at least one other insulating layer. Further, the probe unit substrate according to the second aspect has a feature in which: at least one of the at least one other conductor layer has a conductor pattern and planarization patterns insulated from the conductor pattern; each of the planarization patterns has a plane size greater than the probe mounting pad; and the planarization patterns are located beneath the probe mounting pads. 
   The probe unit substrate according to the third aspect of the present invention has both flatness improvement rings and planarization patterns, and thus comprises: (a) an electrical insulating substrate having a surface; (b) a first conductor layer formed on the surface of the substrate, the first conductor layer including: first conductor patterns; flatness improvement rings surrounding the first conductor patterns with first clearances therebetween; and a second conductor pattern surrounding the flatness improvement rings with second clearances therebetween; (c) a first insulating layer covering over the first conductor layer; (d) at least one other conductor layer formed above the first insulating layer, and at least one other insulating layer covering over the other conductor layer; and (e) probe mounting pads formed on a surface of an uppermost insulating layer of the at least one other insulating layer. Further, the probe unit substrate according to the third aspect has a feature in which: at least one of the at least one other conductor layer has a third conductor pattern and planarization patterns insulated from the third conductor pattern; each of the planarization patterns has a plane size greater than the probe mounting pad; and the planarization patterns are located beneath the probe mounting pads. 
   The probe unit substrate according the present invention has an advantage that the surface irregularity of the multilayer wiring division is alleviated so that the probe mounting pads on its surface neither undulate nor slope because of the formation of the flatness improvement rings or the planarization patterns as described above. Therefore, there is no variation in heights of the tips of the probes that are fixed to a number of the probe mounting pads respectively. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an elevation view of the probe card provided with the probe unit substrate according to the present invention; 
       FIG. 2  is a side sectional view of a part of the probe unit substrate according to the first embodiment of the present invention; 
       FIGS. 3A and 3B  are plan views illustrating a pattern near the through-hole junction pad of the first conductor layer in the first embodiment of the present invention; 
       FIG. 4  is a side sectional view of a part of the probe unit substrate according to the second embodiment of the present invention; 
       FIG. 5  is a side sectional view of a part of the probe unit substrate according to the third embodiment of the present invention; 
       FIG. 6  is a side sectional view of a part of the probe unit substrate according to the fourth embodiment of the present invention; 
       FIG. 7  is a fragmentary plan view of the probe card shown in  FIG. 1  as viewed from the bottom of  FIG. 1 ; 
       FIG. 8  is a fragmentary plan view illustrating a modified planar shape of the planarization pattern; 
       FIG. 9  is a fragmentary plan view illustrating another modified planar shape of the planarization pattern; 
       FIG. 10  is a sectional view taken along the line A-A in  FIG. 9 ; 
       FIG. 11  is a sectional view illustrating a part of the conventional probe unit substrate in a magnified form; 
       FIGS. 12A ,  12 B and  12 C are plan views illustrating a pattern around the through-hole junction pad of the first conductor layer in the prior art; and 
       FIG. 13  is a sectional view illustrating a part of another conventional probe unit substrate in a magnified form. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the present invention will be described in detail below with reference to the drawings.  FIG. 1  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. 
     FIG. 2  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 . 
     FIG. 3A  is a plan view illustrating a pattern near the through-hole junction pad  24  of the first conductor layer  12  (see  FIG. 2 ). 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  FIG. 12A ), the surface drop of the first insulating layer  14  (see  FIG. 2 ) 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  FIG. 3B , 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  FIG. 12B , the risk of short circuit is remarkably reduced. 
     FIG. 4  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. 
     FIG. 5  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  FIG. 4 , 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. 
     FIG. 6  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  FIG. 4 , but further includes the flatness improvement rings  48  shown in  FIG. 2 . Namely, in  FIG. 6 , 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.  FIG. 7  is a fragmentary plan view of the probe card shown in  FIG. 1  as viewed from the bottom of  FIG. 1 , the probe card being equipped with the probe unit substrate  38 , which has the planarization patterns shown in  FIG. 5 . 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  FIG. 5  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 . 
     FIG. 8  is a fragmentary plan view illustrating a modified planar shape of the planarization pattern. This embodiment differs from the embodiment shown in  FIG. 7  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 . 
     FIG. 9  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. 
     FIG. 10  is a sectional view taken along the line A-A in  FIG. 9 . It is assumed that a short circuit place  80  (see also  FIG. 9 ) 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  FIG. 9 , 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  FIG. 9 , 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 .