Abstract:
An electrical interconnect assembly and methods for making an electrical interconnect assembly. In one embodiment, an interconnect assembly includes a flexible wiring layer having a plurality of first contact elements and a fluid containing structure which is coupled to the flexible wiring layer. The fluid, when contained in the fluid containing structure, presses the flexible wiring layer towards a device under test to form electrical interconnections between the first contact elements and corresponding second contact elements on the device under test. In a further embodiment, an interconnect assembly includes a flexible wiring layer having a plurality of first contact terminals and a semiconductor substrate which includes a plurality of second contact terminals. A plurality of freestanding, resilient contact elements, in one embodiment, are mechanically coupled to one of the flexible wiring layers or the semiconductor substrate and make electrical contacts between corresponding ones of the first contact terminals and the second contact terminals. In another embodiment, a method of making electrical interconnections includes joining a flexible wiring layer and a substrate together in proximity and causing a pressure differential between a first side and a second side of the flexible wiring layer. The pressure differential deforms the flexible wiring layer and causes a plurality of first contact terminals on the flexible wiring layer to electrically connect with a corresponding plurality of second contact terminals on the substrate.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to interconnect assemblies and methods for making and using interconnections and more particularly to interconnect assemblies for making electrical contact with contact elements on a substrate such as a semiconductor integrated circuit. More particularly, the present invention relates to methods and assemblies for making interconnections to semiconductor devices to enable test and/or burn-in procedures on the semiconductor devices.  
         BACKGROUND OF THE INVENTION  
         [0002]    There are numerous interconnect assemblies and methods for making and using these assemblies in the prior art. For example, it is usually desirable to test the plurality of dies (integrated circuits) on a semiconductor wafer to determine which dies are good prior to packaging them and preferably prior to being singulated from the wafer. To this end, a wafer tester or prober may be advantageously employed to make a plurality of discreet pressure connections to a like plurality of discreet contact elements (e.g. bonding pads) on the dies. In this manner, the semiconductor dies can be tested prior to singulating the dies from the wafer. The testing is designed to determine whether the dies are non-functional (“bad”). A conventional component of a wafer tester or prober is a probe card to which a plurality of probe elements are connected. The tips of the probe elements or contact elements make the pressure connections to the respective bonding pads of the semiconductor dies in order to make an electrical connection between circuits within the dies and a tester such as an automated test equipment (ATE). Conventional probe cards often include some mechanism to guarantee adequate electrical contact for all contact elements at the bonding pads of the die regardless of the length of the contact elements or any variation in height between the two planes represented by the surface of the die and the tips of the probe pins or contact elements on the probe card. An example of a probe card having such a mechanism can be found in probe cards from FormFactor of Livermore, Calif. (also see the description of such cards in PCT International Publication No. WO 96/38858).  
           [0003]    One type of interconnect assembly in the prior art uses a resilient contact element, such as a spring, to form either a temporary or a permanent connection to a contact pad on a semiconductor integrated circuit. Examples of such resilient contact elements are described in U.S. Pat. No. 5,476,211 and also in co-pending, commonly-assigned U.S. patent application entitled “Lithographically Defined Microelectronic Contact Structures,” Ser. No. 09/032,473, filed Feb. 26, 1998, and also co-pending, commonly-assigned U.S. patent application entitled “Interconnect Assemblies and Methods,” Ser. No. 09/114,586, filed Jul. 13, 1998. These interconnect assemblies use resilient contact elements which can resiliently flex from a first position to a second position in which the resilient contact element is applying a force against another contact terminal. The force tends to assure a good electrical contact, and thus the resilient contact element tends to provide good electrical contact.  
           [0004]    These resilient contact elements are typically elongate metal structures which in one embodiment are formed according to a process described in U.S. Pat. No. 5,476,211. In another embodiment, they are formed lithographically (e.g. in the manner described in the above-noted patent application entitled “Lithographically Defined Microelectronic Contact Structures”). In general, resilient contact elements are useful on any number of substrates such as semiconductor integrated circuits, probe cards, interposers, and other electrical assemblies. For example, the base of a resilient contact element may be mounted to a contact terminal on an integrated circuit or it may be mounted onto a contact terminal of an interposer substrate or onto a probe card substrate or other substrates having electrical contact terminals or pads. The free end of each resilient contact element can be positioned against a contact pad on another substrate to make an electrical contact through a pressure connection when the one substrate having the resilient contact element is pressed towards and against the other substrate having a contact element which contacts the free end of the resilient contact element. Furthermore, a stop structure, as described in the above noted application Ser. No. 09/114,586, may be used with these resilient contact elements to define a minimum separation between the two substrates.  
           [0005]    [0005]FIG. 1 shows one technique for the use of an interconnect assembly. This interconnect  101  includes a chuck structure  117  disposed above a semiconductor wafer  111 , which wafer is supported by a bellows structure  103 . The chuck structure is rigid (not deformable), and the surface of the chuck  117  which includes the contact elements  125  and  127  is also rigid. The bellows structure  103  includes an expandable bellows  105  and intake and outtake ports  107 A and  107 B. In one use of this bellows structure, a fluid, such as water  106  is passed into and out of the bellows structure  103 . A thin steel membrane  109  is welded or otherwise attached to the bellows  105 . The thin membrane may be used to exert uniform pressure against the back of wafer  111  to press the top surface of the wafer against the stop structures  121  and  123 , thereby causing electrical connections between the springs (or other resilient contact elements) on the wafer and the contact elements on substrate  117 . This uniform pressure may overcome some variations in flatness between the meeting surfaces, such as the top surface of the wafer  111  and the surface supporting the stop structures  121  and contact elements  125  and  127 . This thin steel membrane  109  also allows for the transfer of heat to or from the semiconductor wafer  111  which is disposed on top of the membrane  109 . The fluid such as water  106 , may be introduced into the bellows structure under pressure to force the membrane  109  into direct contact with the backside of the wafer  111 .  
           [0006]    This fluid may be heated or cooled in order to control or affect the temperature of the wafer. For example, in a burn-in test of an integrated circuit (or wafer containing integrated circuits), the fluid may be heated to raise the temperature of the wafer and then cooled, and this process may be repeated over several cycles. The chuck  117  includes stop structures  121  and  123  which are proximally adjacent to contact elements  125  and  127  respectively. It may be desirable to place a thermal transfer layer between the membrane  109  and the back of the wafer  111  to improve the heat transfer efficiency between the fluid and the wafer  111 . The contact elements  125  and  127  are designed to make contact with the resilient contact elements  115  and  113  on the wafer  111 . It will be appreciated that there will typically be many more resilient contact elements and many more contact elements than those shown in FIG. 1. The chuck  117  includes wiring or other interconnection in order to connect resilient contact elements  115  and  113 , through contact elements  125  and  127 , to a tester allowing communication of power, signals, and the like between the tester and the semiconductor wafer. The chuck  117  may be held in place by a post  118  in order to allow the wafer  111  to be pressed against the chuck  117  by the expanding of the bellows  105 ; alternatively, the chuck  117  may be pressed and held by a clamshell support which contacts and covers the top of the chuck  117  with a backing plate and may also surround the sides and bottom of the bellows  105 .  
           [0007]    [0007]FIG. 2 shows another example of an interconnect assembly  201 . In this case, a rigid chuck  203  supports a wafer of semiconductor devices  204 . The wafer includes a plurality of contact elements, such as the contact element  210 A which are designed and disposed to make contact relative to resilient contact elements on the wiring substrate  206 . The resilient contact elements  207 ,  209 , and  210  are another example of a resilient element; in this case, they have a generally straight cantilever structure. The stop structures  214 ,  216 , and  218  are attached to a rigid wiring substrate  206  and are designed to define the z separation between the wiring substrate  206  and the wafer  204 . A vacuum port  212  in the wiring substrate  206  allows a vacuum to be formed between the space between the wiring substrate  206  and the chuck  203 . The O-ring seal  205  ensures that a vacuum is formed between the wiring substrate  206  and the chuck  203 . When the vacuum is formed, the wiring substrate  206  is pressed down towards the wafer  204  in order to cause contact to be made between the various resilient contact elements and their corresponding contact elements on the wafer  204 .  
           [0008]    [0008]FIG. 3 shows another example of an interconnect assembly  351  according to the present invention. In this case, a pressure bladder  355  forces the rigid wiring substrate  354  in contact with the wafer  353 . A clamp  355 A is used to press the bladder into the rigid substrate  354 . The wafer  353  sits on top of a rigid chuck  352  and includes a plurality of contact elements, such as the contact element  357 A shown in FIG. 3. As the bladder  355  forces the rigid wiring substrate  354  into contact with the wafer  353 , the stop structures  358 ,  359 , and  360  are brought into contact with the top surface of the wafer  353 . This contact defines a separation between the rigid wiring substrate  354  and the semiconductor wafer  353 . When this contact occurs, the resilient contact elements  357  are brought into mechanical and electrical contact with their corresponding contact elements on the wafer  353 .  
           [0009]    [0009]FIG. 4A shows an example of a flexible probe card device  401 . This probe card device includes a flexible or deformable substrate  402  having contact elements  403 ,  404 , and  405  disposed on one side and a plurality of electrical conductive traces which creates a wiring layer on the opposite side of the flexible substrate  402 . An insulator (not shown) typically covers most of the wiring layer. The contact element  403  is electrically coupled through the via  403 A to the trace  403 B. Similarly, the contact element  404  is electrically coupled through the via  404 A to the trace  404 B on the opposite side of the flexible substrate  402 . Typically, the contact elements  403 ,  404 , and  405  are formed to have approximately the same height and they may be formed by a number of techniques to create a ball grid array or other arrangements of contactors. FIG. 4B shows an example of the use of a flexible probe card device in order to probe or test a semiconductor wafer  430 . In particular, the flexible probe device  420 , which resembles the device  401 , is pressed into contact, by a force F, with the wafer  430 . Each of the respective contact elements on the flexible probe device  420 , such as the contact element  424 , makes a contact with a respective contact element, such as element  434 , on the wafer  430  in order to perform the probe test. The flexible probe device  420  is pressed into contact by use of a press  410  which creates the force F.  
           [0010]    The press  410  has a rigid, flat surface and it presses the flexible probing substrate rigidly along the entire surface of the probing substrate  420 . Referring back to FIG. 4A, the press  410  presses against the surface of the substrate  402  which is opposite the contact elements  403 ,  404 , and  405 . It will be appreciated that an insulating layer may separate the press  410  from the wiring layers  403 B,  404 B and  405 B. If one or more of the contact elements  403 ,  404 , and  405  is smaller (e.g. shorter, etc.) than other contact elements, then it is possible for the smaller contact elements to not make contact when the flexible probing substrate is pressed into contact with a wafer. This is due to the fact that the rigid surface of the press  410  will press the contact elements into contact with a corresponding contact elements on the wafer up to the point when the largest contact elements on the flexible probing substrate have made contact with respective contact elements on the wafer. Thus, the smaller contact elements may not make contact.  
           [0011]    [0011]FIG. 4C shows an example of how irregularities in contact elements and/or irregularities in the surfaces supporting the contact elements can cause a failure to make electrical connection. A force from a rigid press  410  causes the contact elements  424 A and  424 C to make contact (both mechanically and electrically). Contact elements  424 A and  424 C have been formed normally according to a desired size, but contact element  424 B is smaller (e.g. shorter) than the desired size. This difference in size may even be within manufacturing tolerances but nevertheless is relatively shorter than its neighbors. The mechanical contact of contact elements  424 A and  424 C with their corresponding contact elements  434 A and  434 C stops the movement between the layer  420  and the IC  430 , and it becomes impossible to create an electrical contact between contact element  424 B and its corresponding contact element  434 B.  
           [0012]    Similar problems exist with the assemblies shown in FIGS. 1, 2, and  3 . In the case of the assemblies of FIGS. 1, 2, and  3 , the wiring substrate is rigid in all three cases and thus any local differential in heights of the various contact elements (or other irregularities in the two opposing surfaces) may result in a lack of contact being made. Such other irregularities may include a difference in adequate flatness between the two surfaces. The requirement to control the flatness of the two surfaces also increases the manufacturing expense for the surfaces. Furthermore, it is often difficult to achieve and maintain parallelism between the two surfaces, particularly when incorporating the need for precise x, y positional alignment control which may restrict the ability to allow for a compensating tilt. Accordingly, it is desirable to provide an improved assembly and method for making electrical interconnections and particularly in performing wafer probing and/or burn-in testing of semiconductor devices.  
         SUMMARY OF THE INVENTION  
         [0013]    The present invention provides an interconnect assembly and methods for making and using the assembly. In one example of the present invention, an interconnect assembly includes a flexible wiring layer having a plurality of first contact elements and a fluid containing structure which is coupled to the flexible wiring layer. The fluid, when contained in the fluid containing structure, presses the flexible wiring layer towards a device under test to form electrical interconnections between the first contact elements and corresponding second contact elements on the device under test, which may be in one embodiment a single integrated circuit or several integrated circuits on a semiconductor wafer.  
           [0014]    In another example of the present invention, an interconnect assembly includes a flexible wiring layer having a plurality of first contact terminals and a semiconductor substrate which includes a plurality of second contact terminals. A plurality of freestanding, resilient contact elements are mechanically coupled to one of the flexible wiring layer or the semiconductor substrate and make electrical contacts between corresponding ones of the first contact terminals and the second contact terminals.  
           [0015]    In another exemplary embodiment of the present invention, a method of making electrical interconnections includes joining a flexible wiring layer and a substrate together in proximity and causing a pressure differential between a first side and a second side of the flexible wiring layer. The pressure differential deforms the flexible wiring layer and causes a plurality of first contact terminals on the flexible wiring layer to electrically contact with a corresponding plurality of second contact terminals on the substrate.  
           [0016]    In a preferred embodiment, a plurality of travel stop elements may be distributed on one or both of the flexible wiring layer and the substrate.  
           [0017]    It will be appreciated that the various aspects of the present invention may be used to make electrical connection between a single pair of contact elements on two separate substrates or may make a plurality of electrical connections between a corresponding plurality of pairs of contact elements on two different substrates. Various other assemblies and methods are described below in conjunction with the following figures.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements. It is also noted that the drawings are not necessarily drawn to scale.  
         [0019]    [0019]FIG. 1 shows an example of an interconnect assembly which uses a bellows to force a semiconductor wafer into contact with a rigid wiring substrate.  
         [0020]    [0020]FIG. 2 shows another example of an assembly for creating an electrical interconnection between one substrate, such as a semiconductor wafer, and a rigid wiring substrate through the use of a vacuum.  
         [0021]    [0021]FIG. 3 shows another example of an assembly for creating an electrical interconnection between one substrate, such as a semiconductor wafer, and a wiring substrate.  
         [0022]    [0022]FIG. 4A shows an example of a flexible probing device which may be used to probe a semiconductor wafer in a probing operation.  
         [0023]    [0023]FIG. 4B shows an example of an assembly for using a flexible probing device in order to perform a wafer probing operation.  
         [0024]    [0024]FIG. 4C shows how a failed connection can result from the use of an interconnection assembly of the prior art.  
         [0025]    [0025]FIG. 5 is a cross-sectional view showing an example of an interconnection assembly according to one embodiment of the present invention.  
         [0026]    [0026]FIG. 6A is a cross-sectional view showing another embodiment of an interconnection assembly according to the present invention.  
         [0027]    [0027]FIG. 6B is a cross-sectional view of another embodiment of an electrical interconnection assembly according to the present invention.  
         [0028]    [0028]FIG. 6C shows in partial view and in cross-sectional view an example of an electrical interconnection assembly in use according to one embodiment of the present invention.  
         [0029]    [0029]FIG. 6D shows in cross-sectional view how a flexible wiring layer of the present invention can deform in order to provide an electrical connection despite irregularities in surfaces and/or contact elements.  
         [0030]    [0030]FIG. 7A shows another embodiment of the present invention of an electrical interconnection assembly.  
         [0031]    [0031]FIG. 7B shows a top view of the flexible wiring layer  705  shown in FIG. 7A.  
         [0032]    [0032]FIG. 8 shows a partial view of another example of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0033]    The present invention relates to interconnection assemblies and methods for making interconnections and particularly to interconnect assemblies and methods for making mechanical and electrical connection to contact elements on an integrated circuit. The following description and drawings are illustrative of the invention and are not to be construed as limiting the invention. Numerous specific details are described to provide a thorough understanding of the present invention. However, in other instances, well known or conventional details are not described in order to not unnecessarily obscure the present invention in detail.  
         [0034]    [0034]FIG. 5 shows one example of an electrical interconnection assembly according to the present invention. The assembly includes a fluid containing structure  509  which includes a chamber  519  for containing the fluid. The fluid is retained by the inner walls of the structure  509  and by the flexible wiring layer  507  which may, in one embodiment, be similar to the flexible probing device shown in FIG. 4A. Disposed below the flexible wiring layer  507  is a device under test such as the integrated circuit or semiconductor wafer  505 . The integrated circuit  505  is supported by a backing plate  503  which may be rigid. The backing plate  503  is secured to the fluid containing structure  509  by bolts  511 A and  511 B as shown in the cross-sectional view of FIG. 5. An O-ring seal  527  (or other sealing mechanisms which may be used) serves to seal the chamber  519  from leakage of fluid between the flexible wiring layer  507  and the edge of the assembly  509 . The O-ring seal  527  is under a foot of the edge of assembly  509  and is pressed into tight contact with the flexible wiring layer  507 . Fluid may be introduced into the chamber  519  through the inlet port  521  and fluid may be removed from the chamber  519  through the outlet ports  525  and  523 . Fluid which is removed from these outlet ports may be pumped or transferred to a temperature controller  515  which then provides fluid having a desired temperature to a pump and pressure controller  517  which, in turn, returns the fluid through the port  521  back into the chamber  519 . It may be desirable to maintain the fluid in a continuously circulating state in order to maintain an accurately controlled temperature and in order to maintain a desired pressure.  
         [0035]    [0035]FIG. 5 shows the state of the interconnection assembly before introducing a fluid, such as a liquid or a gas, into the chamber  519 . In particular, the flexible wiring layer has been placed in proximity, and typically close proximity (e.g. about 75 to about 750 microns), to the contact surface of the integrated circuit  505 . Typically, the electrical contact elements on the flexible wiring layer, such as contact elements  533 A,  533 B and  533 C will not be in mechanical contact and will not be in electrical contact with the corresponding contact elements on the integrated circuit, such as the contact elements  532 A,  532 B and  532 C, when the fluid has not been introduced into the chamber  519 . After mounting the integrated circuit  505  or other device under test in proximity to the flexible wiring layer  507 , then the fluid may be introduced into the chamber  519  to create a pressure differential between one side of the flexible wiring layer  507  and the other side of the flexible wiring layer  507 , thereby pressing the flexible wiring layer into contact with the contact elements of the integrated circuit  505 . This is shown in the partial view of FIG. 6C which shows a portion of the flexible wiring layer  507  being brought into contact with the contact elements of the integrated circuit  505  which is supported by the backing plate  503  as shown in FIG. 6C. The pressure created by the fluid is represented by the pressure  690  shown in FIG. 6C. Because the flexible wiring layer is deformable, portions in local regions of the flexible wiring layer may slightly deform relative to other regions of the flexible wiring layer under the pressure of the fluid in order to create contact. When the fluid is removed from the chamber  519 , the flexible wiring layer  507  may return to its non-deformed state.  
         [0036]    This provides a solution for the situation in which the heights of the contact elements differ enough so that using conventional assembly techniques, the smaller height contact elements will not make an electrical connection. This solution also accounts for a lack of parallelism between the two surfaces and for non-planarities in the surfaces.  
         [0037]    As shown in FIGS. 5 and 6C, stop structures, such as stop structures  531 A,  531 B, and  531 C may be disposed on the upper surface of the integrated circuit  505  in order to define the minimum separation between the integrated circuit  505  and the local regions of the flexible wiring layer  507 . Using the stop structures to define this separation will allow the use of considerable pressure exerted by the fluid in order to ensure adequate electrical contact across the entire surface of the integrated circuit  505  without at the same time damaging the contact elements, such as the resilient, freestanding contact elements  532 A,  532 B and  532 C shown in FIG. 5. FIG. 6C shows the stop structures in action as they prevent the flexible wiring layer  507  from being pressed further towards the surface of the integrated circuit  505  by the fluid pressure  690 . In an alternative embodiment, the stop structures may be attached to the surface of the flexible wiring layer, or stop structures may be disposed on both surfaces.  
         [0038]    [0038]FIG. 6D shows an example of how a flexible wiring layer can deform or flex in a local region in order to provide an electrical connection despite irregularities in surfaces and/or contact elements. The example of FIG. 6D shows the use of resilient contact elements, however, it will be appreciated that in an alternative example, rigid contact elements (e.g. C4 balls) may be used rather than resilient contact elements. The flexible wiring layer  507 , under the influence of the fluid pressure  690 , deforms locally around the contact element  533 B. The deformation stops when the element  533 B makes mechanical (and hence electrical) contact with the freestanding, resilient contact element  532 B, which is shorter than the freestanding, resilient contact elements  532 A and  532 C. Without the deformation, electrical connection may not occur between contact elements  534 B and  533 B (see, for example, FIG. 4C where no deformation occurs since the planar surface of press  410  is rigid). The flexible wiring layer  507  is capable of providing electrical contact between corresponding contact elements even when the surfaces are irregular (e.g. bumpy or uneven) or when they are not exactly parallel or even when the contact elements are irregular (e.g. the heights of the contact elements vary too much). When resilient contact elements are used as the connection elements between the two surfaces, they may accommodate the “local” variations or irregularities in the two surfaces (e.g. over a distance range of up to about 2000 to 5000 microns), such that the flexible wiring layer may not need to be so flexible that it deforms over such a local range, but in this case the flexible wiring layer should still be deformable enough that it can accommodate longer range variations or irregularities (e.g. a lack of parallelism between the two surfaces over a range of several inches across the flexible wiring layer).  
         [0039]    The flexible wiring layer  507  may be used with or without stop structures. The stop structures may be desirable when the pressure differential between the two surfaces of the flexible wiring layer is so large that the contact elements could be damaged from the resulting force or when it is desirable to provide a force larger than the minimum to allow for manufacturing tolerances in the flexible wiring layer, chucks, contact elements, etc. The height and placement of the stop structures should be designed to allow for normal flexing of the resilient contact element and to allow for the flexible wiring layer to deform at least beyond a local range. The flexible wiring layer should be flexible, and/or deformable, enough to allow for local deformations. In the case where resilient contact elements are used, the flexible wiring layer should be deformable enough to mold, under pressure, to a substrate&#39;s shape (e.g. a wafer&#39;s shape) and yet still be stiff enough over a local range to not deform too much between travel stops. The flexible wiring layer should be more flexible in the case where rigid contact elements (e.g. C4 balls as in FIG. 4C) are used between the two surfaces. Furthermore, given that, in most cases, the flexible wiring layer will be used again and again for testing different ICs (or different wafers), the flexible wiring layer should be able to return to its non-deformed shape after the pressure differential is relieved. This is achieved by operating the flexible wiring layer within the elastic deformation regime of the material in the flexible wiring layer.  
         [0040]    It will be appreciated that the flexible wiring layer  507  may be formed out of any number of materials, such as a polyimide material which allows for sufficient local flexibility and/or deformability in small areas. Furthermore, the flexible wiring layer may contain multiple wiring layers disposed between layers of insulators as is well-known in the art of creating multiple layer conductive substrates such as printed circuit boards or flexible printed circuit boards. The flexible wiring layer  507  may be used to make electrical connections with a single integrated circuit either before or after packaging of the integrated circuit or may be used to make electrical connections to one or more of the integrated circuits on a semiconductor wafer or portion of a semiconductor wafer. Furthermore, the flexible wiring layer  507  may be used to make electrical connections to a passive connector assembly such as an interposer or other type of connection substrates which do not include integrated circuits or semiconductor materials. Thus, the flexible wiring layer  507  may be used to test a single integrated circuit or one or more integrated circuits on a semiconductor wafer or on a connection substrate such as an interposer. It will be further understood that the flexible wiring layer  507  in conjunction with the assembly of the present invention may be used with various types of connection elements including, for example, resilient, freestanding connection elements such as those noted above or other types of connection elements such as bonding pads, C4 balls, elastomeric balls, pogo pins, as well as other contact elements which are known in the art and the connection elements may be disposed on one or both of the flexible wiring layer.  
         [0041]    In the case of full wafer testing, with wide temperature variations, the material chosen for the flexible wiring layer should have a TCE (thermal coefficient of expansion) close to or identical to the TCE of silicon. This can be achieved by suitable choice of material (e.g. Upilex S or Arlon 85NT) or even further enhanced by adding well-known low expansion layers (such as Invar) to the flexible wiring layer.  
         [0042]    [0042]FIG. 6A shows another example of an interconnection assembly according to the present invention. This interconnection assembly also includes a chamber  519  which is used to receive and contain a fluid which is used to create a pressure differential across the flexible wiring layer  507 . The flexible wiring layer  507  includes contact elements disposed on the side of the flexible wiring layer  507  which faces the integrated circuit  505 . These contact elements, such as contact element  533 C, are used to make electrical contact with corresponding contact elements on the integrated circuit  505 . As in the case of the assembly shown in FIG. 5, when fluid is introduced into the chamber  519 , the flexible wiring layer  507  is pressed towards the integrated circuit  505  such that the contact elements on the integrated circuit  505  make electrical contact with the corresponding contact elements on the flexible wiring layer  507  shown in FIG. 6A. As shown in FIG. 6A, the flexible wiring layer  507  includes several active or passive electrical devices such as devices  605 ,  607 , and  609  which are attached to the side of the flexible wiring layer  507  which is not adjacent to the integrated circuit  505 . These electrical devices may be integrated circuits which are used to provide signals to or receive signals from the integrated circuit  505  or they may be other active devices or they may be passive devices (e.g. decoupling capacitors) which may by advantageously placed in close proximity to one or more contact elements on the integrated circuit  505 . This allows the capacitance of the decoupling capacitor to be small and yet achieve an adequate decoupling effect. The electrical devices may be mounted on the flexible wiring layer  507  within the chamber  519 , such as the devices  605  and  607 , or they may be mounted outside of the chamber  519  as in the case of device  609 . By mounting devices such as devices  605  and  607  within the chamber  519  on the side  611  of the flexible wiring layer  507 , these devices within the chamber may be cooled by the fluid which is introduced into the chamber  519 . It is a desirable feature to make a short length electrical contact through the flexible wiring layer. In the implementation shown in FIG. 6A, the flexible wiring layer should be capable of holding the pressurized fluid without leaking. This can be achieved by using filled vias or by inserting a continuous membrane such as silicone across the pressure plenum. In a preferred embodiment, a silicone membrane having a thickness of about 0.015 inches (380 microns) was used.  
         [0043]    The assembly  601  shown in FIG. 6A also includes one or more cavities in which a fluid such as a gas or a liquid is allowed to flow through. These cavities  603  may be used to cool or alternatively heat the integrated circuit  505  during testing or burn-in of the integrated circuit  505 . A cavity  603  may run the entire length or only a portion of the entire length of the backing plate  503 .  
         [0044]    It is generally desirable that the flexible wiring layer  507  be a thin layer so as to provide an acceptable thermal conductance between the fluid within the chamber  519  and the integrated circuit  505 . For example, where an extensive semiconductor wafer testing is to take place and the self-heating of the wafer is undesirable, a cooled fluid may be used within the chamber  519  to keep the integrated circuit  505  at a desired temperature. At the same time, a coolant may be circulated through the channels  603 . Alternatively, where a stress test is to be performed on the integrated circuit  505  in conjunction with the electrical testing, a heated fluid may be introduced into the chamber  519  and/or into the channel  603 . The temperature of the fluid within the chamber  519  may be controlled as well as the temperature of the fluid within the channel  603  in order to achieve a desired temperature for the testing procedures of the integrated circuit  505 .  
         [0045]    It will be appreciated that the flexible wiring layer  507  may act as a conventional probe card in redistributing and interconnecting the contact elements on the integrated circuit to a test device such as an automatic test equipment (ATE). Thus, the flexible wiring layer  507  may provide for contact pitch transformation with its wiring layers. These wiring layers serve to interconnect the contacts on the integrated circuit with the ATE device and with the various circuits mounted on the surface  611  of the flexible wiring layer  507 , such as the devices  605  and  607 . Typically, the flexible wiring layer  507  will include a bus which delivers signals to and from the ATE, such as the bus  610  shown in FIG. 6A.  
         [0046]    [0046]FIG. 6B shows another alternative embodiment of the present invention in which the assembly  631  includes a flexible wiring layer  633  which in this case includes stop structures, such as the stop structure  641 , and includes resilient contact elements such as the resilient contact element  639 . Thus, unlike the assembly  610  shown in FIG. 6A, the flexible wiring layer includes both stop structures and resilient contact elements which may be used to make contact with contact elements on an integrated circuit  635 , such as the contact element  637 . In all other respects, the assembly of FIG. 6B resembles the assembly of FIG. 5. It will be appreciated that the assembly of FIG. 6B may be used to test or burn-in semiconductor wafers which do not include resilient contact elements but rather include merely bonding pads or other contact elements (e.g. C4 balls) located on the surface of the semiconductor wafer.  
         [0047]    An alternative embodiment of an assembly of the present invention may use a vacuum generated between the integrated circuit  505  and the flexible wiring layer  507  in order to create a pressure differential between one side and the other side of the flexible wiring layer  507 . For example, if a vacuum port is located in the backing plate  503 , and this port is coupled to a vacuum pump, a vacuum may be drawn in the chamber created by the rigid backing plate  503  and the flexible wiring layer  507 . If normal air pressure is maintained in the chamber  519 , when the vacuum is drawn, the flexible wiring layer  507  will be pressed toward the integrated circuit  505 , causing contact to be made between the corresponding contact terminals on the flexible wiring layer  507  and the integrated circuit  505 .  
         [0048]    [0048]FIGS. 7A and 7B show another embodiment of an interconnection assembly which utilizes a flexible wiring layer according to the present invention. The assembly  701  shown in FIG. 7A includes a plenum which includes at least one fluid port  723 . While FIG. 7A shows port  723  on the bottom of the assembly, it will be appreciated that the port  723  may be located on the side of the assembly so that the bottom is flat and portless. The fluid port  723  provides fluid into the chamber  721  in order to deform the flexible wiring layer  705  and press it towards the device under test such as the integrated circuit  707 . The integrated circuit  707  is drawn to a vacuum chuck  709  using conventional techniques associated with vacuum chucks which are known in the art. The vacuum chuck may be used to control the wafer temperature by using techniques which are well-known in the art. In FIG. 7A, an air cooled vacuum chuck is shown. The vacuum chuck  709  includes a heat sink  711  which is mounted on the upper surface of the vacuum chuck  709 . The vacuum chuck  709  is coupled by flanges  712  to the plenum  703  as shown in FIG. 7A. In one embodiment, the vacuum chuck  709  and the heat sink  711  may be made from aluminum and the flanges  712  and the plenum  713  may be formed from titanium. In the example of FIG. 7A, the integrated circuit  707  includes resilient contact elements, such as the contact elements  737 A and  737 B, each of which are attached to contact elements  735 A and  735 B which may be bonding pads on the integrated circuit  707 .  
         [0049]    It will be appreciated that reference being made to an integrated circuit  707  is one example of various devices under test. Rather than a single integrated circuit, the device under test shown in FIG. 7A may be a complete semiconductor wafer having many integrated circuits or a portion of such a wafer or may be a packaged integrated circuit or may be a passive interconnection substrate such as an interposer for a probe card or a wiring substrate. Thus, it will be appreciated that when reference is made to an integrated circuit in the various embodiments of the invention, that this reference is solely for the purpose of convenience and that any of these alternative devices under test may be utilized in the assemblies of the present invention.  
         [0050]    As shown in FIG. 7A, the flexible wiring layer  705  includes stop structures  733 A and  733 B and includes the contact elements  731 A and  731 B. It will also be appreciated that the flexible wiring layer includes the various conductive traces along its surface or within its structure and includes an interconnection bus to an ATE or to another type of testing device.  
         [0051]    The flexible wiring layer  705  is held in place within the assembly  701  by an O-ring seal  714  which is clamped at the periphery of the flexible wiring layer  705  as shown in the top view of FIG. 7B. The clamps  715 A and  715 B, as shown in the cross-sectional view of FIG. 7A, secure the O-ring to the edge of the layer  705  and these clamps are secured into the plenum  703  by bolts  716 A and  716 B. In an alternative embodiment, the O-ring seal  714  may be sandwiched between the flexible wiring layer  705  and the plenum  703 . The clamps  715 A and  715 B would be straight, rather than curved, or have an “L” shape and would secure the layer  705  tightly to the O-ring seal  714 .  
         [0052]    The operation of the assembly  701  will now be described. Typically, the device under test, such as an integrated circuit or a complete semiconductor wafer, is placed against the vacuum chuck such that the contact elements face away from the vacuum chuck. The device under test is drawn toward the chuck by creating a vacuum within the interior of the chuck as is known in the art. Holes in the surface of the chuck draw the wafer or other device under test securely to the surface of the chuck. Then the contact elements on the device under test are aligned in x and in y and in θ relative to the contact elements on the flexible wiring layer  705  in order to allow proper contact to be made between corresponding contact elements on the layer  705  and the device under test  707 . At this point, the z spacing between the device under test  707  and the flexible wiring layer  705  may be decreased so that the two surfaces are in close proximity. Next, the chamber  721  is filled with a fluid in order to “inflate” the layer  705  such that it is pressed towards the device under test  707  causing contact to be made between corresponding contact elements between the two surfaces.  
         [0053]    [0053]FIG. 8 shows another example of the invention. In this example, a device under test  805  is attached to a flexible layer  809  which is held in the assembly  801 . The clamps  817 A and  817 B secure the flexible layer  809  to the O-ring seal  816 , thereby providing a seal for the fluid receiving chamber  811 , which is formed by the base  814  and the layer  809 . Fluid (e.g. a liquid or pressurized air) may be introduced into the chamber  811  through the port  811 A. The fluid, when introduced, will push the layer  809  so that the device under test  805  (which may be a semiconductor wafer having resilient contact elements  807 ) is pushed toward the wiring layer  803 , which is similar to the flexible wiring layer  507  except that layer  803  need not be flexible/deformable. When the device under test  805  is pushed sufficiently toward the layer  803 , the resilient contact elements  805  make electrical contact with corresponding contact elements (e.g. contact pads  804 ) on the layer  803 . The layer  803  is attached to a chuck  802  which itself is secured to the flange  815 . In an alternative embodiment, the resilient contact elements may be attached to layer  803  and may make contact to contact pads on the device under test  805 . In other embodiments, different contact elements (e.g. balls) may be used on one or both of the surfaces.  
         [0054]    It will be appreciated that the interconnection assembly of the present invention may be utilized for semiconductor probing, such as probing of complete semiconductor wafers, or in the burn-in of singulated integrated circuits or the burn-in of complete semiconductor wafers. In the case of probing, the assembly may be mounted in the test head and aligned in x, y, and z and θ relative to either known positions on the semiconductor wafer or known positions on a probing device such as a wafer prober which are known relative to known positions on a semiconductor wafer. Then the flexible wiring layer may be brought into close proximity with the semiconductor wafer and then inflated in order to cause electrical contact. In the case of a burn-in operation, the device under test may be mounted in the assembly and aligned with the contacts on the flexible wiring layer and then moved to a burn-in environment and connected to test equipment and then the flexible wiring layer is “inflated” or otherwise drawn towards the device under test in order to make electrical contact.  
         [0055]    In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes can be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are accordingly to be regarded in an illustrative sense rather than in a restrictive sense.