PATENT ABSTRACT
A probe card includes a flexible membrane, a plurality of probes attached to the flexible membrane, and a layer of foam connected to the flexible membrane so that when the probes are moved into the flexible membrane, the layer of foam is also deflected to produce a counteracting force at the probes. A plurality of push rods are used to transfer the force at the contacts to the foam layer. The foam layer is attached to a rigid plate or push plate. A guide plate includes openings through which the push rods pass. The guide plate supports the push rods along their length and reduces the spacing between the push rods at the flexible member when compared to the spacing of the push rods at the foam layer.

PATENT DESCRIPTION
This application is a divisional of U.S. patent application Ser. No. 10/884,552, filed Jul. 2, 2004, now U.S. Pat. No. 7,230,438, which is a divisional of U.S. patent application Ser. No. 10/208,900, filed on Jul. 30, 2002, now issued as U.S. Pat. No. 6,759,861. These applications are incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to an apparatus and method for providing electrical contacts. More specifically, the present invention relates to membrane probe cards used in making a large number of electrical components. 
   BACKGROUND OF THE INVENTION 
   As more and more capability is being designed into electronic components, such as microprocessors, the components are becoming increasingly complex. The more complex an electrical component becomes, the greater number of semiconductor device fabrication steps needed to form the electrical component. Semiconductor devices, such as microprocessors, are generally made from a wafer of semiconductive material. Many individual semiconductor devices are formed on a single wafer. All of the devices are made simultaneously on the wafer. Hundreds of individual semiconductor processes, which include deposition of material, ion implantation, etching, and photolithographic patterning, are conducted on a wafer to form a number of individual semiconductor devices. The wafers are sizeable. As a result, the effectiveness of each semiconductive process on each device may vary somewhat. In addition, each step or semiconductive process used to form the devices is not necessarily uniform. Generally, the semiconductive process has to perform within a desired range. The end result due to variations in the semiconductive processes as well as the variation in position is that the semiconductive devices formed may vary from one wafer to another. In addition, the semiconductive devices may vary from other semiconductive devices on the wafer. 
   The current practice is to test all the semiconductor devices on a wafer prior to singulation. Generally, two tests are conducted. The first test is conducted to determine if any of the individual semiconductive devices on the wafer are bad. A second test is conducted to determine a performance parameter for the good semiconductive devices on the wafer. For example, currently wafers have up to 300 microprocessors. Of course, the number of devices formed on a wafer will be higher in the future. Each of these microprocessors is tested to determine if the microprocessor is good. The speed of the microprocessor is determined in a second test. Once measured, the speed of the microprocessor is saved and the location of the microprocessor on the wafer is noted. This information is used to sort the microprocessors based on performance at the time the wafer is sliced and diced to form individual dies, each of which has a microprocessor thereon. 
   Each semiconductive device formed on a wafer has a number of electrical contacts. To test all the semiconductive devices on a wafer at once, many, if not all of the electrical contacts, have to be contacted. For example, testing a number of individual contacts on a wafer commonly requires upwards of 3000 different individual contacts to be made across the surface of the wafer. Testing each contact requires more than merely touching each electrical contact. An amount of force must be applied to a contact to break through any oxide layer that may have been formed on the surface of the contact. Forming 3000 contacts which are not all at the same height and not all in the same plane is also difficult. As a result, a force has to be applied to the contacts to assure good electrical contact and to compensate for the lack of planarity among the contacts. 
     FIG. 1  shows a membrane probe card  100  which is currently used to conduct high frequency sort and test procedures. The membrane probe card  100  includes a rigid substrate  110  and a plurality of probes  120 . The probes  120  include an attached end  122  and a free end  124 . The free end  124  of the probe  120  is used to contact an individual die  130 . More specifically, the free end  124  of the probe  120  is used to contact individual electrical contacts  132  on the die  130 . Only one die  130  is shown in  FIG. 1 . It should be noted that a wafer includes many dies that have not been sliced or diced into individual dies. The probe  120  includes a sharp bend  126  and also includes a more gentle bend  128 . The more gentle bend  128  allows the probe  120  to act as a leaf spring. As shown in  FIG. 1 , the electrical contacts  132  of the die  130  have just come into contact with the individual probe  120  and specifically the free end  124  of the probe  120 . 
   To overcome nonplanarity among the contacts  132  and to assure good electrical contact by passing through any oxidation layer on the contacts  132 , the die is over driven into the rigid substrate  110 . In other words, the die  130  or device under test is pressed into the probes  120  to assure that the each electrical contact  132  is contacted by a probe tip  124 , and to assure that the oxidation layer has been punctured, so that good electrical contact is made. As shown by the phantom lines in  FIG. 1 , the device under test  130  is more closely spaced with respect to the substrate  110  so that the probes deflect and produce a larger force at the contacts  132 . 
   The currently used membrane probe card system has a number of shortcomings. Among the shortcomings is the difficulty in controlling the amount of force produced by the probe tip. The amount of force produced at the probe tip  124  is related to the deflection of the spring shaped probe  120 . If the planarity of the contacts  132  varies widely, the deflection of individual probes  120  also varies. In turn, the force at each probe tip  124  also varies widely and is difficult to control. Overdriving the probe cards not only causes variation in the force produced by the probe  120 , but also causes damage to both the probe tip  124  and the product or device under test  130 . 
     FIG. 2  shows a side view of a prior art membrane probe card  200 . The membrane probe card includes a substrate  210  and a membrane  230 . The membrane  230  is attached to the substrate  210 . Attached to the membrane are a plurality of contacts  220 . The contacts  220  are short and do not accommodate a lack of planarity. Any lack of planarity is accommodated by the membrane  230 . Membrane probe card cards  200  also have shortcomings. The shortcomings include the fact that the membrane  230  may be damaged when the device under test is overdriven into the membrane probe card  200 . 
   Thus, there is a need for a probe card which allows for force control at the probe tips so that the components of the probe card or the device under test are not damaged during testing. There is also a need for a probe card that has a more uniform or constant force at the probe tip. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is pointed out with particularity in the appended claims. However, a more complete understanding of the present invention may be derived by referring to the detailed description when considered in connection with the figures, wherein like reference numbers refer to similar items throughout the figures and: 
       FIG. 1  illustrates a side view of a prior art probe card. 
       FIG. 2  illustrates a side view of a prior art membrane probe card. 
       FIG. 3  illustrates a schematic view of a contactor which uses the thin film probe card contact drive system of this invention. 
       FIG. 4  illustrates an exploded side view of the thin film probe card contact drive system of this invention. 
       FIG. 5  illustrates an exploded side view of another embodiment of the thin film probe card contact drive system of this invention. 
       FIG. 6  illustrates a side view of the flexible membrane, the contacts and the push rods of the thin film probe card contact drive system of this invention. 
   

   The description set out herein illustrates the various embodiments of the invention and such description is not intended to be construed as limiting in any manner. 
   DETAILED DESCRIPTION 
     FIG. 3  illustrates a schematic view of a contactor which uses the thin film probe card contact drive system of this invention. The contactor  300  includes a contact drive system  310 , a thin film substrate or flexible member  340  having contacts  342 , and electrical circuitry  350 . The electrical circuitry  350  will provide input to the contacts  342  on the thin film substrate or flexible member  340  and receives the output from the thin film substrate or flexible member  340  on line  354 . The electrical circuitry  350  may include both the hardware and the software necessary to conduct tests on a device under a test  360 . 
   The device under test  360  includes a set of electrical pads or contacts  362  which correspond to the contacts  342  on the flexible member or thin film substrate  340 . The device under test  360  is mounted or attached to a driver  370 . The driver  370  holds the device under test  360  and raises the device under test  360  until the electrical pads  362  contact the contacts  342  of the flexible member or thin film substrate  340 . The thin film probe card contact drive system  310  includes a push plate  312  and a foam layer  320 . A plurality of push rods  322  transfer the load at the flexible member or thin film substrate  340  to the foam pad  320 . Typically there is a push rod  322  that corresponds to a position on the flexible member or thin film substrate  340  opposite a contact  342 . The push rod  322  transfers force from the contact  342 , or more specifically from the flexible member or thin film substrate  340  to the foam layer  320 . The foam layer  320  is made of a foam having a close cell. The foam also has a high degree of elastic memory. The foam also has a specific durometer characteristic indicative of the elasticity and flexiblity of the foam layer  320 . Typically, higher durometer readings indicate increased difficulty associated with pressing a push rod  322  into the layer of foam  320 . 
     FIG. 4  illustrates an exploded side view of the thin film probe card contact drive system  410  of this invention. The thin film probe card contact drive system  410  includes a push plate  312 . Attached to the push plate is a layer of foam  320 . A series or plurality of push rods  322  are positioned to impact or press into the flexible member or thin film substrate  340 . The push rods  322  include a first end  323  which contacts the foam pad  320 , and a second end  321  which contacts a thin film substrate or flexible member  340 . Attached to the thin film substrate or flexible member  340  are a set of probe tips  342 . The probe tips  342  are attached on one side of the thin film substrate or flexible member  340 . A push rod  322 , or more specifically, the end  321  of the push rod  322 , is typically positioned on the opposite side of the thin film substrate or flexible member  340  opposite from the probe tips  342 . 
   A guide block  400  is positioned around the push rods  322 . The guide block has openings  402  therein. The push rods  322  pass through the openings  402  in the guide block  400 . The guide block  400  is made of a material that will allow the push rods  322  to slip within the openings  402  of the guide block  400 . It should be noted that the pitch or spacing of the push rod ends  323  is farther apart than the spacing of the push rod ends  321  contacting or near the thin film substrate or flexible member  340 . Thus, the guide block  400  serves several purposes, including supporting the column or push rod  322  to prevent columnar failure along the length of the push rod  322 . Another purpose is to allow the pitch or spacing between the push rods  322  to be farther apart at the first end  323  contacting the layer of foam  320  than at the second end  321  where the push rod contacts flexible member or thin film substrate  340 . When the spacing between the push rods  322  is increased, the amount of force applied to the push rod  322  can be more carefully controlled. In other words, with increased spacing between the push rods  322  at the first ends  323 , the total area over which the push rods  322  act is effectively larger. Furthermore, the effect on the area where a first push rod  322  acts on the foam pad  320  is more isolated from the area where a second push rod (adjacent the first push rod)  322  acts. In other words, the foam pad  320  will act more independently to produce independent forces as the spacing between the first ends  323  of the push rods is increased. For a particular set of push rods  322 , the pitch of the push rod  322  at the foam layer  320  is higher than the pitch the set of push rods at the thin substrate or flexible element  340 . As shown in  FIG. 4 , the push rods  322  angle toward one another, or from the first end  323  to the second end  321  so that a device under test (shown in  FIG. 3 ) having very closely spaced contacts can be tested. Since the spacing between the ends  323  of probes at the foam pad  320  is increased, an independent and controlled force is delivered to each and every contact or probe  342 . 
   When a device under test (shown in  FIG. 3 ) is placed in contact with the probes  342 , the push rods  322  are compressed between the thin film substrate or flexible media  340  and the layer of foam  320 . The layer of foam  320  and the push rods  322  serve as a backing to the individual contacts or probe tips  342  attached to the flexible membrane or thin film substrate  340 . The amount of force produced at each probe tip  342  can be controlled by selecting different materials for the layer of foam  320 . In addition, the spacing or pitch between the ends  323  of the push rods  322  is increased when compared to the pitch between the ends  321  of the push rods  322  at the thin film substrate or flexible member  340  so that the amount of force applied to one probe tip  342  is substantially independent of force applied to an adjacent probe tip  342 . Typically the pitch between the first ends  323  of the push rods  322  will be higher, or the spacing between the ends  323  of the push rods  322  will be greater, at the foam layer  320  than the pitch between the second ends  321  of the push rods  322 . 
   It should be noted that the push rods  322  form an array or geometric shape which corresponds to the array of probe tips  342 . The array of probe tips  342  matches the array of contacts on the device under test (shown in  FIG. 3 ). The array of first ends  323  of the push rods  322  formed at the foam layer  320  will have a spacing that is slightly greater then the array of the probe tips  342 . For the sake of simplicity, a simple array having only two lines of push rods  322  is shown in  FIG. 4 . Generally, however, the array will and include additional push rod elements. Of course the actual geometric shape of the array of push rods  322  and the ends of the push rods is dependent on the shape of the array of contacts of the device under test (shown in  FIG. 3 ). 
     FIG. 5  shows an exploded view of yet another embodiment of the thin film probe card contact drive system  500 . The main difference between the thin film probe card drive system  500  of  FIG. 5  compared to the thin film probe card contact drive system  410  shown in  FIG. 4 , is the addition of a second guide plate or block  510  and a third guide plate or block  520 . The guide plates  510  and  520  include openings  512  and  522 , respectively. The push rods  322  shown in  FIG. 5  are longer then the push rods  322  shown in  FIG. 4 . A push rod  322  will pass through an opening  402  in the first guide plate or guide block  400 , an opening  512  in the second guide plate or guide block  510 , and an opening  522  in the third guide block  520 . At each guide block  400 ,  510 ,  520 , the pitch between the individual push rods  322  increases as compared to the pitch between the probe tips  342 . As a result, the pitch between the ends  323  contacting the foam pad or foam layer  320  is greater than the pitch between the push rods  322  between the second guide block  510  and the third guide block  520 . Similarly the pitch between the second guide block  510  and the third guide block  520  is greater then the pitch between the first guide block  400  and the second guide block  510 . The push rods are made of a material that can be compressed, such as epoxy, fiberglass or brass. Each of the guide blocks  400 ,  510 ,  520  is made of a material that will allow the guide or the push rods  322  to glide through the openings  402 ,  512 ,  522  within the respective guide blocks  400 ,  510 ,  520 . 
     FIG. 6  illustrates a side view of the flexible membrane or thin film substrate  340  the contacts or probes  342  and the push rods  322 .  FIG. 6  shows a close up of these various components.  FIG. 6  illustrates that for each contact  342  positioned on one side of the thin film substrate or flexible membrane  340 , there is a push rod  322  placed on the opposite side of the thin film substrate  340 . Specifically, the end  321  of the push rod  322  contacts one side of the thin film substrate  340  opposite a contact  342 . The thin film substrate or flexible membrane  340  is sandwiched or positioned between the end  321  of the push rod  322  and the contact  342 . 
   In operation, the device under test will come into contact with the individual pins  342 . The thin film membrane  340  will compress slightly, but a force will be transferred to the push rod  322 . The force is transferred up to the foam layer  320 , which is selected so that a certain amount of pressure on the push plate  312  (shown in  FIG. 5 ) would produce a selected amount of force in each of the contacts or probes  342 . The push rod  322  is in compression between the contact  342  and the layer of foam  320  (shown in  FIG. 5 ). 
   This structure has many advantages. The thin film probe card contact drive system allows for force control at the probe tips so that the components of the probe card are not damaged. The force control also prevents damage to the device under test. The force produced at the probe tips  342  by the thin film probe card contact drive system is also more uniform or constant. In other words, the force at each individual probe tip is closer to the force at other individual probe tips. The foam layer  320  provides for a more uniform force, since the foam is being compressed when the push rod pushes against the foam. The force produced at the probe tip  342  is controlled by selecting different types of foam. Foam typically has a durometer rating, which is a measure of the stiffness of the foam. A higher stiffness foam produces a higher force at the probe tip  342 . The spacing of the push rods  322  at the foam  320  interface is controlled so that adjacent push rods  322  act independently or substantially independently of one another. The diameter of the push rods  322  at the foam  320  interface can also be changed to alter the amount of force at the probe tips  342 . The spacing or the pitch is typically larger at the end  323  of the push rod  322  contacting the foam pad  320 , so that the force can be dispersed over a larger area at the foam layer. The diameter of the push rods  322  at the foam layer  320  is also larger, so that the force can be dispersed over a larger area at the foam layer  320 . Thus, a large force can be placed on the contact or probe tip  342  with little pressure on the rigid push plate  312  attached to the foam layer  320 . Still a further advantage is that the membrane or thin film  340  associated with the probe card does not have to carry all the force necessary to place the probe tips  342  in contact with the contacts of the device under test. The result is a contact system which is more durable. 
   The foregoing description of the specific embodiments reveals the general nature of the invention sufficiently that others can, by applying current knowledge, readily modify and/or adapt it for various applications without departing from the generic concept, and therefore such adaptations and modifications are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. 
   It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Accordingly, the invention is intended to embrace all such alternatives, modifications, equivalents and variations as fall within the spirit and broad scope of the appended claims.