Abstract:
A contact for use in a contact set assembly. The contact spans a space which separates a lead of an integrated circuit to be tested and a pad of a load board interfacing with the tester. The contact construction provides electrical communication between integrated circuit lead and the load board pad. Included is an insulating lamina which comprises, in part, a contact. A conductive lamina overlies at least a portion of the insulating lamina. The laminar construction and size and shape of conductive traces applied to a ceramic lamina enable parameters of the contact to be provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This is a regular application filed under 35 U.S.C. § 111(a) claiming priority, under 35 U.S.C. § 119(e) (1), of provisional application Ser. No. 60/747,031 previously filed May 11, 2006 under 35 U.S.C. § 111(b). 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention deals broadly with testers for evaluating integrated circuit devices and structure for mating leads of the integrated circuit device to corresponding pads of a load board that interfaces with the tester. More narrowly, however, it deals with contacts positioned in an array for electrically connecting the integrated circuit leads with their corresponding load board pads and providing structure for efficiently transmitting test signals. A specific focus of the invention is a particular contact to be used in such an array in order to maintain impedance at a desired level.  
       BACKGROUND OF THE INVENTION  
       [0003]     Integrated circuit tester devices have long been used in industry to test and evaluate the quality of the device being tested. Signal integrity is, of course, an important consideration in conducting testing. It is also desirable to maintain impedance through a conducting portion of a contact interconnecting the integrated circuit lead to its corresponding load board pad at a particular desired level. For example, in the case of testing of many types of devices, 50 ohms is a desired level.  
         [0004]     The impedance that is achieved is a function of a number of factors. These include length of conduction path, material of which the conductive structure is made, etc.  
         [0005]     The present invention is a contact which improves the testing function beyond what is achieved with other contacts. It takes into consideration the dictates of the prior art and overcomes problems extant therein.  
       SUMMARY OF THE INVENTION  
       [0006]     The invention is a contact which spans a space which separates a lead of an integrated circuit to be tested by a tester apparatus and a pad of a load board interfacing with the tester. The contact thereby provides electrical communication between the integrated circuit lead and the load board pad. The contact includes an insulating lamina which has oppositely facing sides and a profile which includes a first end engageable by the lead of the integrated circuit. The profile also has a second end which is in engagement with a pad of the load board. A conductive lamina overlies at least a portion of the insulating lamina. The conductive lamina also extends from the first end of the insulating lamina to the second end thereof. The thickness of the conductive lamina is expanded at the first and second ends of the insulating lamina. Consequently, a first end of the conductive lamina is more effectively engaged by the lead of the integrated circuit, and a second end of the conductive lamina, proximate the load board, more effectively engages the pad of the load board.  
         [0007]     In one embodiment of the invention, the conductive lamina comprises a first trace which is applied to one side of the insulating lamina. This first conductive trace extends from the first end of the insulating lamina to its second end. This embodiment also includes a second conductive trace which overlies at least a part of the other side of the insulating lamina and also extends from the first end to the second end of that lamina. In a preferred embodiment, the first and second conductive traces extend beyond the first end of the insulating lamina and include means, extending from the conductive traces, for cutting through oxide build-up on the lead of the integrated circuit which engages the contact. Typically, tin oxide will build up on the surface of the integrated circuit device lead.  
         [0008]     The means for cutting through an oxide build-up, it is intended, would include an elongated blade edge. Such a blade edge would extend from each conductive trace at its first or upper end. In one envisioned construction, these blade edges would extend generally parallel to one another. Similarly, they would, in turn, be generally parallel to a plane defined by a surface of the contact. Because of intended elastomeric mounting of the contact, the blade edges, when engaged by a lead of an integrated circuit, would move linearly in a direction of the lay of the blade edges when they are not engaged by an integrated circuit.  
         [0009]     It will be understood that the conductive laminae or traces can be either sandwiched between lateral insulating layers or together, sandwich an insulating layer between two conductive laminae. The specific construction would, of course, depend upon the application of the tester, whether the housing in which the elastomeric mounting of the contact was accomplished were metallic, etc.  
         [0010]     Certain embodiments of the invention can provide for redundant contacting. Such a concept could enable reduction in size of components to support pitch lower than 0.5 mm. With use of a ceramic insulating material, the effects E-field radiating could be greatly reduced or eliminated.  
         [0011]     It is envisioned that the insulating lamina would be made of a ceramic material. It has been found that such a material tends to be the best of a number of choices to serve such a purpose.  
         [0012]     The present invention is thus an improved contact for use in integrated circuit testing. More specific features and advantages obtained in view of those features will become apparent with reference to the DETAILED DESCRIPTION OF THE INVENTION, appended claims and accompanying drawing figures. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a side elevational view of a portion of a set of contacts in accordance with the present invention spanning a space between, and interconnecting, corresponding leads of an integrated circuit device and corresponding pads of a load board which interfaces with a tester;  
         [0014]      FIG. 2  is a perspective view of the portion illustrated in  FIG. 1 ;  
         [0015]      FIG. 3  is a side elevational view of a ceramic lamina contact having conductive trace material plated on a side of the contact;  
         [0016]      FIG. 4  is a perspective view of a further embodiment of the invention illustrating a ceramic contact array wherein a controlled impedance trace is sandwiched between two nonconductive layers;  
         [0017]      FIG. 5  is a view similar to  FIG. 4  but illustrating full pad interface;  
         [0018]      FIG. 6  is a view similar to  FIG. 1  illustrating the second embodiment of the invention;  
         [0019]      FIG. 7  is an elevational view illustrating a third contact embodiment interconnecting the integrated circuit lead and the load board pad;  
         [0020]      FIG. 8  is a view similar to  FIG. 2  illustrating a contact including an attached decoupling component; and  
         [0021]      FIG. 9  is a side elevational view of the contact of  FIG. 8 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     Referring now to the drawing figures wherein like reference numerals denote like elements throughout the several views,  FIG. 2  illustrates a contact array  10  for use in a test socket. Such an array  10  employing contacts  12  in accordance with the present invention uses substantially cylindrical elastomers  14 ,  16  to mount the contacts  12  to a housing  18 . The housing  18 , in turn, enables contacts to span the distance between leads  20  of an integrated circuit device  22  to be tested, when the device is in an appropriate location, and pads  24  on a load board  26  which interfaces with the tester apparatus (not shown).  FIG. 2  illustrates a segment of a test socket mounting four contact elements. It will be understood, of course, that this number is not exclusive. In fact, the typical integrated circuit will dictate the employment of considerably more contacts so that at least one contact will be present to provide electrical signal transmission between each lead  20  of the integrated circuit device  22  and its corresponding load board pad  24 .  
         [0023]     The contact set illustrated in  FIG. 2  is shown in more detail in  FIG. 1 . Each contact  12  is provided with an insulating lamina  28 . The lamina  28 , in turn, has a conductive trace  30  applied to each of opposite sides thereof. A trace  30  is applied in an overlying relationship to at least a portion of the insulating lamina  28  and extends from a first end  32  of the insulating lamina  28  to a second end  34  thereof.  FIG. 3  illustrates a trace  30  which generally takes the form of a band  36  applied to a ceramic insulating lamina so that, when an integrated circuit  22  is engaged with upper ends of the contacts  12  comprising the array  10 , an electrical path will be provided between each integrated circuit lead  20  and the corresponding load board pad  24 . Such a band  36  can be of any width or length to match impedance of the device I/O. Its width can also vary to generate stubs (not shown) that could optimally match device I/O to a certain impedance or represent an inductive or capacitive element.  
         [0024]     It will be understood that a symmetrical trace  30  would be applied to the other side of the contact insulating lamina  28  also. Symmetry of the traces  30  will afford a substantially identical redundancy.  
         [0025]     As seen in  FIG. 1 , the point of engagement of the contact with the lead  20  of the integrated circuit  22  is conductive. Similarly,  FIG. 1  illustrates contact  12  with the load board pad  24  as having a width substantially as great as the ceramic insulating lamina  28 . As a result, signals will be transmitted through the contact  12  in an efficient manner. Again, the symmetry of the traces  30  on opposite sides of the same contact insulating lamina  28  will provide substantially the same response irrespective of signal transmission path.  
         [0026]     The type of ceramic material selected and the material and geometry of the traces  30  are chosen in order to achieve a desired impedance. In a particular application, an impedance of 50 ohms is desirable. The shape and route of the traces  30  can be varied, as necessary, to achieve the impedance desired. Further, a decoupling component  38  could be mounted on the contact trace  30  to create a smart contact which would allow for production testing mimicking real-world applications.  
         [0027]     Further, the relative location of the traces  30  on the insulating lamina  28  would facilitate the accommodation of smaller pitch devices. Thus, the particular shape, size and orientation of traces  30  are factors to be considered in creating the contacts  12 .  
         [0028]      FIGS. 4 and 5  illustrate, in different degrees of pad interfacing, a second contact embodiment array. Mounting of each contact  12  is similar to that employed in mounting the embodiment previously discussed.  FIG. 4  is a view illustrating a recessed pad construction.  FIG. 5  is a view illustrating full pad interface. Components are, otherwise, substantially the same as components illustrated in  FIGS. 1 and 2 .  
         [0029]      FIG. 6  illustrates a series of contacts  12  wherein the conductive trace  30  is interior to the contact  12 . That is, the trace is laterally central in the contact  12  with nonconductive laminae  40 ,  40 ′ sandwiching the conductive trace  30  therebetween. At ends of the traces  30 , however, engagement portions  42 ,  44 , extending generally normal to a plane defined by the internal trace  30 , is provided. One transverse portion  42  is engaged by the lead  20  of the integrated circuit device  22 , and another transverse portion  44  engages a corresponding load board pad  24 . Such a contact construction offers variation in design in view of desired impedance, facilitation of good inter-engagement and significant signal transmission. The conductive portion of a contact so constructed is physically separated farther from an adjacent contact&#39;s conductive portion. This results in improved crosstalk performance. The “I-beam” construction is structurally strong and will result in enhanced mechanical performance. The top and bottom portions  42 ,  44  can be recessed from edges to accommodate recessed device I/O leads  20  and result in the contact being able to be incorporated into a totally metal housing for improved thermal and ground inductance.  
         [0030]     Again,  FIGS. 8 and 9  illustrate the application of a decoupling component  38 . The construction and advantages of such an embodiment are discussed hereinbefore.  
         [0031]      FIG. 7  illustrates a further embodiment of a contact in accordance with the present invention. In some degree, the contact of  FIG. 7  is similar to the contacts shown in  FIG. 6 . That is, nonconductive laminae  40 ,  40 ′ sandwich a conductive trace element  30  therebetween. In fact, however, the contact of  FIG. 7  is a hybrid of the contacts of  FIG. 1  and  FIG. 6 . That is so because a central core  46  is provided from a nonconductive ceramic material. Dual traces  30 ,  30 ′ are applied to oppositely-facing sides of the central core  46 , and the nonconductive side components  40 ,  40 ′ are overlain to complete the contact. In this embodiment, however, means for cutting through oxide build-up on the integrated circuit device lead are provided. Such means can take the form of an elongated blade edge  48 ,  48 ′ extending from one or both of the conductive traces  30 ,  30 ′. As seen best in  FIG. 7 , the blade-like elements  48 ,  48 ′ extend distally with respect to the traces  30 ,  30 ′ and are engaged by a lead  20  of the integrated circuit device  22 . Typically the device leads  20  are made of matte tin. When this material is used for the leads, tin oxide can build up and diminish the integrity of operation of the contact transmission element. Because of the blade edges  48 ,  48 ′ of the traces  30 ,  30 ′, a very fine etch through the tin oxide will occur and the integrity of signal transmission will not be diminished. The blade edge size can be increased or the radius changed to adjust and control the forces applied to the device I/O to minimally break through tin oxides without creating damage to the device I/O leads  20 .  
         [0032]     It will be understood that the degree of pressure with which the blade edges  48 ,  48 ′ are applied to the tin oxide is a function of the elastomers  14 ,  16  by which the contacts  12  are mounted. Appropriate elastomers will be selected depending upon the degree of oxidation of the integrated circuit leads and other factors.  
         [0033]     As will be seen, the present inventive concept includes use of a ceramic material to form one or more laminae of a transmission contact  12  with one or more conductive traces  30 ,  30 ′ applied to nonconductive ceramic portions. By varying the laminar structure, the size, shape and other features of the traces and other factors, a desired impedance level can be achieved. Conductive traces and the particular construction involved enables a contact  12  to be used with recessed pad devices or, when the ceramic laminae are manipulated, with metal housings. In consequence, the electrical match, inductance and crosstalk are improved. The principles involved can be applied when using a greater than air dielectric material to plate surfaces of a contact. Again, matching characteristics and greatly reduced signal propagation to other contacts in the housing structure will be improved. That is, crosstalk will be reduced.  
         [0034]     It will be understood that this disclosure, in many respects, is only illustrative. Changes may be made in details, particularly in matters of shape, size, material, and arrangement of parts without exceeding the scope of the invention. Accordingly, the scope of the invention is as defined in the language of the appended claims.