Abstract:
A fixture for holding an integrated circuit. The integrated circuit is of the type having a front side and an opposing back side. The fixture positions the integrated circuit for simultaneously electrically probing and viewing both the front side and the back side of the integrated circuit. A supporting brace provides a support that is immobile in at least a first direction, against which to cooperatively brace the integrated circuit. A first jaw piece is disposed adjacent the supporting brace. The first jaw piece has a vee shape for receiving a first corner of the integrated circuit and cooperatively aligns the integrated circuit into a position for simultaneously electrically probing and viewing the front side and the back side of the integrated circuit. An adjustable brace provides a movable second position in the first direction relative to the supporting brace, against which to cooperatively brace the integrated circuit with the supporting brace. A second jaw piece is disposed adjacent the adjustable brace. The second jaw piece also has a vee shape for receiving a second corner of the integrated circuit, where the second corner is disposed in an opposing position to the first corner of the integrated circuit and cooperatively aligns the integrated circuit into a position for simultaneously electrically probing and viewing the front side and the back side of the integrated circuit. Retaining means adjustably retain the adjustable brace relative to the supporting brace.

Description:
FIELD 
     This invention relates to the field of integrated circuit testing. More particularly the invention relates to a fixture for holding integrated circuits for testing. 
     BACKGROUND 
     Integrated circuits are preferably tested in either wafer form or packaged form. When the integrated circuits are in either of these two forms, they are relatively easy to handle. For example, before a wafer is diced into individual integrated circuit chips, the wafer is large and easy to mount and position relative to a test station. Because of the size of the wafer, it is relatively easy to hold the wafer from positions on the wafer that do not physically interfere with either electrically probing or viewing the device under test. Similarly, packaged devices are also relatively easy to test compared to individual devices. Once the individual integrated circuit device is mounted and electrically connected to the packaging, the package is easily mounted and electrically connected to a test station. 
     However, sometimes it is necessary to test an integrated circuit that is neither in wafer form nor in package form. This need might arise either between the time that the wafer is diced and the individual devices are packaged, or after a device has been removed from its packaging for some reason, such as during failure analysis. 
     Special problems are encountered when testing individual devices. For example, because of the small size of individual devices, compared to either wafers or packages, they are more difficult to hold. Further, and also because of the small size of individual devices, they tend to be more difficult to hold in a manner that allows the device to be viewed or electrically probed. This problem is compounded when it is important for both the front and back surfaces of the device to be probed or viewed during testing. Further, individual devices tend to be far more fragile than packaged devices, and thus they are more easily damaged during testing than are packaged devices. 
     What is needed, therefore, is a fixture that allows an individual integrated circuit device to be safely held such that both surfaces of the integrated circuit can be probed, viewed, or both. 
     SUMMARY 
     The above and other needs are met by a fixture for holding an integrated circuit. The integrated circuit is of the type having a front side and an opposing back side. Thus, it is desired that the fixture allow for positioning the integrated circuit for simultaneously electrically probing and viewing both the front side and the back side of the integrated circuit. 
     A supporting brace provides a support that is immobile in at least a first direction, against which to cooperatively brace the integrated circuit. A first jaw piece is disposed adjacent the supporting brace. The first jaw piece receives the integrated circuit and cooperatively aligns the integrated circuit into a position for simultaneously electrically probing and viewing both the front side and the back side of the integrated circuit. The first jaw piece also has a vee shape for receiving a first corner of the integrated circuit. 
     An adjustable brace provides a movable second position in the first direction relative to the supporting brace, against which to cooperatively brace the integrated circuit with the supporting brace. A second jaw piece is disposed adjacent the adjustable brace. The second jaw piece receives the integrated circuit and cooperatively aligns the integrated circuit into a position for simultaneously electrically probing and viewing both the front side and the back side of the integrated circuit The second jaw piece also has a vee shape for receiving a second corner of the integrated circuit, where the second corner is disposed in an opposing position to the first corner of the integrated circuit. 
     Retaining means adjustably retain the adjustable brace relative to the supporting brace. 
     Thus, this embodiment of a fixture according to the present invention holds an individual integrated circuit by opposing corners between two braces. The adjustable brace, in cooperation with the retaining means, provides compressive force in the first direction on the integrated circuit in cooperation with the supporting brace, which is immobile in the first direction. The first jaw piece and the second jaw piece, by holding the integrated circuit at the corners, allow for both the front side and the back side of the integrated circuit to be accessible. Thus, both the front side and the back side of the integrated circuit can be either electrically probed or viewed while the integrated circuit is mounted within the fixture. 
     In various preferred embodiments of the invention, the retaining means include a thumbscrew, spring, or both. First and second guide rails are preferably provided, disposed in an immobile position relative to the first direction, and receive the adjustable brace and guide it in the first direction toward the supporting brace. The first and second jaw pieces preferably have a thickness that is about twice the thickness of the integrated circuit, and a vee shaped cross section of about 120 degrees. This provides a self centering action on the integrated circuit in two different directions. The self centering action in one direction is provided by the general vee shape of the jaw pieces, and the self centering action in the other direction is provide by the vee shaped cross section. The general vee shape of the jaw pieces is preferably a ninety degree angle, to match the opposing corners of the integrated circuit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages of the invention are apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein: 
     FIG. 1 is a top plan view of a first embodiment of the invention, 
     FIG. 2 top plan view of a second embodiment of the invention, 
     FIG. 3 is a cross sectional view of the second embodiment of the invention, 
     FIG. 4 is top plan view of a third embodiment of the invention, and 
     FIG. 5 is a top plan view of a fourth embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIG. 1, there is depicted a first embodiment of a fixture  10  according to the present invention. In this embodiment, the largest element of the fixture  10  is the supporting brace  12 , which has a generally circular outline, and is generally disk shaped. It is appreciated that the supporting brace  12  can have other forms as well, but this simplified form serves well for the purpose of explaining the construction and operation of the fixture  10 . 
     The supporting brace  12  is preferably formed of a durable material, so that it does not unduly deteriorate with use. In addition, the material selected for the supporting brace  12  is preferably rigid, so that it does not unduly deform under the stresses that are induced when the integrated circuit  22  is retained in the fixture  10 , as more completely described below. Materials such as, but not limited to, steel, aluminum, and fluoropolymer resins sold under the trademark TEFLON tend to work well for construction of the supporting brace  12 . However, other materials that are consistent with the design criteria described above may also be used to construct the supporting brace  12 . 
     A first jaw piece  18  is disposed adjacent to the supporting brace  12 . While in some embodiments the first jaw piece  18  is permanently connected to the supporting brace  12  in some appropriate manner, in a most preferred embodiment the first jaw piece  18  is selectively removable from the supporting brace  12 , so that first jaw pieces  18  of various sizes and shapes can be used with the fixture  10 , as described more completely below. One method of disposing the first jaw piece  18  is to press fit the supporting brace  12  into a slot in the first jaw piece  18 . In this manner, the fixture  10  can be used with integrated circuits  22  (shown in phantom) of different sizes. 
     As seen in FIG. 1, the first jaw piece  18  is generally vee shaped. One corner of the integrated circuit  22  is received by the vee portion of the first jaw piece  18 , between the two legs of the first jaw piece  18 . In this manner, the first jaw piece  18  provides a self centering action against the integrated circuit  22  in this first orientation, which is within the plane of the integrated circuit  22 . The angle of the vee of the first jaw piece  18  is most preferably ninety degrees, as this coincides with the angle most commonly used for the corners of an orthogonal integrated circuit  22 . However, in other embodiments, the angle of the vee is selected as something other than ninety degrees, which may or may not coincide with the angle of the corners of the integrated circuit  22 . 
     As indicated by the position of the phantom edge line of the integrated circuit  22  in FIG. 1, and as more explicitly depicted in the cross sectional view of FIG. 3, the first jaw piece  18  also preferably has a vee shaped cross section. In this manner, portions of both the top and bottom edges of the first jaw piece  18  extend to a very small degree over the front and back surfaces of the integrated circuit  22 , respectively. The vee shaped cross section of the first jaw piece  18  provides for a self centering of the integrated circuit  22  in a second orientation, which is perpendicular to the plane of the integrated circuit  22 , and also provides a retaining action against the integrated circuit  22 . In this manner, pressure may be applied against either or both of the front surface and the back surface of the integrated circuit  22 , such as might be applied by electrical probes, without the integrated circuit  22  becoming dislodged from the fixture  10 . 
     In a most preferred embodiment the angle of the vee cross section of the first jaw piece  18  is about 120 degrees. When the first jaw piece  18  has a thickness of approximately twice the thickness of the integrated circuit  22 , this angle of the vee cross section provides adequate retaining of the integrated circuit  22 , without the top and bottom edges of the first jaw piece  18  extending to so great an extent across the front and back surfaces of the integrated circuit  22  as to substantially impair the ability to electrically probe or view the front and back surfaces of the integrated circuit  22 . This angle also works well with other thicknesses of the first jaw piece  18 , because it tends to reduce chipping and cracking of the integrated circuit  22  at the edges of the integrated circuit  22 . 
     The first jaw piece  18  is preferably formed of a durable material so as to have a long utile life. In addition, the first jaw piece  18  is preferably formed of a material that provides an adequate resistance to the pressure that is placed upon it while the integrated circuit  22  is retained in the fixture, as described more completely below. However, another preferred characteristic of the first jaw piece  18  is that it provides for some degree of compression from the integrated circuit  22 , so that there is some amount of flexibility within the first jaw piece  18  when the integrated circuit  22  is pressed against it and retained by it. This latter characteristic also helps to reduce chipping and cracking of the integrated circuit  22  at the edges of the integrated circuit  22 . Fluoropolymer resins sold under the trademark TEFLON have been found to be a good material for the construction of the first jaw piece  18 . However, other materials that are compatible with the design criteria given above may also be selected for fabrication of the first jaw piece  18 . 
     In one special embodiment, where both the supporting brace  12  and the first jaw piece  18  may or may not be constructed of the same material, such as fluoropolymer resins sold under the trademark TEFLON, the supporting brace  12  and the first jaw piece  18  may or may not be formed from a single piece of material, and may or may not be selectively detachable one from the other. In this embodiment, the fixture  10  tends to accept integrated circuits  22  of only a set range of sizes, as the first jaw piece  18  can not be removed from the supporting brace  12  and replaced with an alternate jaw piece of a different size. However, in those instances where only integrated circuits  22  of the size compatible with the first jaw piece  18  are to be tested, this embodiment may be the simplest and least expensive embodiment. 
     An adjustable brace  16  is provided to cooperatively brace the integrated circuit  22  with the supporting brace  12 . The adjustable brace  16  provides a movable second position relative to the supporting brace  12 . In the embodiment depicted in FIG. 1, the adjustable brace  16  fits within an orifice  15  formed within the supporting brace  12 . It is appreciated that the adjustable brace  16  can have other forms as well, but this simplified form serves well for the purpose of explaining the construction and operation of the fixture  10 . 
     As also described in regard to the supporting brace  12 , the adjustable brace  16  is preferably formed of a durable material, so that it does not unduly deteriorate with use. In addition, the material selected for the adjustable brace  16  is preferably rigid, so that it does not unduly deform under the stresses that are induced when the integrated circuit  22  is retained in the fixture  10 , as more completely described below. Materials such as, but not limited to, steel, aluminum, and fluoropolymer resins sold under the trademark TEFLON tend to work well for construction of the adjustable brace  16 . However, other materials that are consistent with the design criteria described above may also be used to construct the adjustable brace  16 . 
     A second jaw piece  20  is disposed adjacent to the adjustable brace  16 . As mentioned above, while in some embodiments the second jaw piece  20  is permanently connected to the adjustable brace  16  in some appropriate manner, in a most preferred embodiment the second jaw piece  20  is selectively removable from the adjustable brace  16 , so that second jaw pieces  20  of various shapes and sizes can be used with the fixture  10 . One method of disposing the second jaw piece  20  is to press fit the adjustable brace  16  into a slot in the second jaw piece  20 . As described above, in this manner, the fixture  10  can be used with integrated circuits  22  of different sizes. 
     As seen in FIG. 1, and similar to the construction of the first jaw piece  18 , the second jaw piece  20  is generally vee shaped. One corner of the integrated circuit  22  is received by the vee portion of the second jaw piece  20 , between the two legs of the second jaw piece  20 . In this manner, the second jaw piece  20  provides a self centering action against the integrated circuit  22  in the first orientation. The second jaw piece  20  preferably receives the second corner of the integrated circuit  22 , which is disposed in an opposing position relative to the first corner of the integrated circuit  22 , which is received by the first jaw piece  18 . The angle of the vee of the second jaw piece  20  is most preferably ninety degrees, as this coincides with the angle most commonly used for the corners of an orthogonal integrated circuit  22 . However, in other embodiments, the angle of the vee is selected as something other than ninety degrees, which may or may not coincide with the angle of the corners of the integrated circuit  22 . 
     As indicated by the position of the phantom edge line of the integrated circuit  22  in FIG. 1, and again as more explicitly depicted in the cross sectional view of FIG. 3, the second jaw piece  20  also preferably has a vee shaped cross section. In this manner, portions of both the top and bottom edges of the second jaw piece  20  extend to a very small degree over the front and back surfaces of the integrated circuit  22 , respectively. The vee shaped cross section of the second jaw piece  20  provides for a self centering of the integrated circuit  22  in the second orientation, and also provides a retaining action against the integrated circuit  22 , all in cooperation with the first jaw piece  18 , as described above. In this manner, pressure may be applied against either or both of the front surface and the back surface of the integrated circuit  22 , such as might be applied by electrical probes, without the integrated circuit  22  becoming dislodged from the fixture  10 . 
     In a preferred embodiment the angle of the vee cross section of the second jaw piece  20  is the same as that of the first jaw piece  18 , which in the most preferred embodiment is about 120 degrees. When the second jaw piece  20  has a thickness of approximately twice the thickness of the integrated circuit  22 , this angle of the vee cross section provides adequate retaining of the integrated circuit  22 , without the top and bottom edges of the second jaw piece  20  extending to so great an extent across the front and back surfaces of the integrated circuit  22  as to substantially impair the ability to electrically probe or view the front and back surfaces of the integrated circuit  22 . This angle also works well with other thicknesses of the second jaw piece  20 , because it tends to reduce chipping and cracking of the integrated circuit  22  at the edges of the integrated circuit  22 . 
     As described above in regard to the first jaw piece  18 , the second jaw piece  20  is preferably formed of a durable material so as to have a long utile life. In addition, the second jaw piece  20  is preferably formed of a material that provides an adequate resistance to the pressure that is placed upon it while the integrated circuit  22  is retained in the fixture, as described more completely below. However, another preferred characteristic of the second jaw piece  20  is that it provides for some degree of compression from the integrated circuit  22 , so that there is some amount of flexibility within the second jaw piece  20  when the integrated circuit  22  is pressed against it and retained by it. This latter characteristic also helps to reduce chipping and cracking of the integrated circuit  22  at the edges of the integrated circuit  22 . Fluoropolymer resins sold under the trademark TEFLON have been found to be a good material for the construction of the second jaw piece  20 . However, other materials that are compatible with the design criteria given above may also be selected for fabrication of the second jaw piece  20 . 
     In one special embodiment, where both the adjustable brace  16  and the second jaw piece  20  may or may not be constructed of the same material, such as fluoropolymer resins sold under the trademark TEFLON, the adjustable brace  16  and the second jaw piece  20  may or may not be formed from a single piece of material, and may or may not be selectively detachable one from the other. In this embodiment, the fixture  10  tends to accept integrated circuits  22  of only a set range of sizes, as the second jaw piece  20  can not be removed from the adjustable brace  16  and replaced with an alternate jaw piece of a different size. However, in those instances where only integrated circuits  22  of the size compatible with the second jaw piece  20  are to be tested, this embodiment may be the simplest and least expensive embodiment. 
     Most preferably, the second jaw piece  20  is smaller than the first jaw piece  18 . By smaller it is meant that the two legs that form the vee of the second jaw piece  20  do not extend to as great a length outward from the vee intersection as do the two legs that form the vee of the first jaw piece  18 . This is depicted in FIG.  1 . All other dimensions of the second jaw piece  20  can be identical to the corresponding dimensions of the first jaw piece  18  in this embodiment, although that is not a requirement. It is appreciated that it is also not a requirement that the second jaw piece  20  be the one of the two jaw pieces  18  and  20  that is smaller in this embodiment. It is equally applicable for the first jaw piece  18  to be smaller than the second jaw piece  20  in this embodiment, as described above or for one leg of the first jaw piece  18  or the second jaw piece  20  or both to be shorter than the other leg for better retention of non square integrated circuits  22 . 
     One benefit of constructing one of the jaw pieces  18  and  20  to be smaller than the other is that a wider range of sizes of integrated circuited  22  can then be accommodated by the fixture  10 . In the embodiment depicted in FIG. 1, integrated circuits  22  having a range of sizes from as large as the opening  15  in the supporting brace  12  to as small as a side length just greater than the length of the legs of the second jaw piece  20  are accommodated by the fixture  10 . This is possible because the second jaw piece  20 , because the legs are shorter than those of the first jaw piece  18 , can fit between the legs of the first jaw piece  18  to some extent. In this manner, the longer legs of the first jaw piece  18  provide additional stability for larger integrated circuits  22 , while the shorter legs of the second jaw piece  20  provide the ability for smaller integrated circuits  22  to be held by the fixture  10 . 
     In the embodiment depicted in FIG. 1, the adjustable brace  16  slides between first guide rail  14   a  and second guide rail  14   b . The first guide rail  14   a  and second guide rail  14   b  are disposed in an immobile position relative to the first direction, and guide the adjustable brace  16  toward the first jaw piece  18  on the supporting brace  12 . The first guide rail  14   a  and second guide rail  14   b  are preferably formed of a durable material that does not unduly wear away as the adjustable brace  16  slides back and forth along the first guide rail  14   a  and second guide rail  14   b  during use of the fixture  10 . 
     Selection of an appropriate material may depend in part on the material selected for the fabrication of the adjustable brace  16 . For example, it may be preferred to select a combination of materials that generate a low degree of friction between the pieces, without the need for lubrication. By removing lubrication from the fixture  10 , the possibility of contaminating the integrated circuit  22  with the lubrication is reduced. Forming either the first guide rail  14   a  and second guide rail  14   b  or the adjustable brace  16  out of fluoropolymer resins sold under the trademark TEFLON is one good combination. The other piece can be formed of a metal, or may also be formed of fluoropolymer resins sold under the trademark TEFLON. 
     It is desired that, in the selection of the construction materials for the first guide rail  14   a  and second guide rail  14   b  and the adjustable brace  16 , the fixture  10  is able to operate smoothly, so that an even pressure is applied to the integrated circuit  22 . It is also desired that the mating surfaces between the first guide rail  14   a  and second guide rail  14   b  and the adjustable brace  16  not wear away excessively. 
     In one special embodiment in which the first guide rail  14   a  and second guide rail  14   b  are formed of the same material as that selected for the construction of the supporting brace  12 , the first guide rail  14   a  and second guide rail  14   b  are formed as a single piece with the supporting brace  12 , as depicted in FIG.  1 . However, in alternate embodiments the first guide rail  14   a  and second guide rail  14   b  are separate pieces from the supporting brace  12 , and are held immobile in regard to the first direction by either mounting them to the supporting brace  12 , or mounting both the first guide rail  14   a  and second guide rail  14   b  to another element that holds them immobile in the first direction. 
     A retaining means is used to maintain compression of the integrated circuit  22  between the first jaw piece  18  of the supporting brace  12  and the second jaw piece  20  of the adjustable brace  16 . In the embodiment depicted in FIG. 1, the retaining means is provided by a spring  24 , which is held in compression to urge the adjustable brace  16  along the first guide rail  14   a  and second guide rail  14   b  toward the first jaw piece  18  of the supporting brace  12 , and adjustably retains the adjustable brace  16  relative to the supporting brace  12 . In the embodiment depicted in FIG. 1, a first end of the spring  24  is disposed adjacent the adjustable brace  16  and the second end of the spring  24  is disposed adjacent a back portion of the supporting brace  12 . In other embodiments, such as those embodiments in which the adjustable brace does not fit within the orifice  15  of the supporting brace  12 , the second end of the spring  24  is disposed adjacent a different element, such as an element on which the first guide rail  14   a  and second guide rail  14   b  are mounted. 
     In alternate embodiments, such as that depicted in FIG. 2, the retaining means is a thumbscrew  25  that retains the adjustable brace  16  in regard to an element that is immobile in relation to the first direction. In this manner, pressure is applied to the integrated circuit  22  by manually sliding the adjustable brace  16  toward the first jaw piece  18  of the supporting brace  12 , and securing the integrated circuit  22  between the first jaw piece  18  and the second jaw piece  20 . Then the thumbscrew  25  is tightened, retaining the adjustable brace  16  in place relative to the supporting brace  12 . 
     In the embodiment of the fixture  10  depicted in FIG. 2, other elements have also been added to the more basic design of the fixture  10  as depicted in FIG.  1 . These additional elements are more clearly understood with additional reference to the cross sectional view of FIG.  3 . Top plate  26  overlies the supporting brace  12  and the adjustable brace  16 , and serves to provide additional stability to the adjustable brace  16  and rigidity to the fixture  10  as a whole. The top plate  26  forms an access port  29 , through which at least the first jaw piece  18  and the second jaw piece  20  are seen and accessed, so that the integrated circuit  22  can be placed in the fixture  10 . The access port  29  also allows the integrated circuit  22  to be electrically probed and viewed from the top side of the fixture  10 . 
     Further, as depicted in FIG. 2, the thumbscrew  25  selectively retains the adjustable brace  16  against the top plate  26  by moving in slot  23  formed in the top plate  26  when the thumbscrew  25  is loose, and drawing the adjustable brace  16  against the top plate  26  when the thumbscrew  25  is tightened. 
     In one embodiment, both a thumbscrew  25  and a spring  24  are used in the retaining means. In this manner, the pressure applied against the integrated circuit  22  by the spring  24  can be “locked” by tightening the thumbscrew  25 . In this manner, the adjustable brace  16  tends to not inadvertently spring open, such as might occur if the fixture  10  is unintentionally knocked. The thumbscrew  25  can also be used as a handle, from which the adjustable brace  16  is drawn back against the pressure of the spring  24 , and then gently allowed to slide forward under the pressure of the spring  24  to secure the integrated circuit  22  between the first jaw piece  18  and the second jaw piece  20 . 
     As depicted in FIG. 3, a bottom plate  28  can also be added to the fixture  10 , thus further enclosing and protecting the interior workings of the fixture  10 , including elements such as the supporting brace  12 , the adjustable brace  16 , the first guide rail  14   a  and second guide rail  14   b , and the spring  24 . The bottom plate  28  forms an access port  30 , through which at least the first jaw piece  18  and the second jaw piece  20  are seen and accessed, so that the integrated circuit  22  can be placed in the fixture  10 . The access port  30  also allows the integrated circuit  22  to be electrically probed and viewed from the back side of the fixture  10 . In this embodiment, the thumbscrew  25  can be configured to pass completely through a slot formed in the adjustable brace  16  and thread into the bottom plate  28 . Thus, the slot of the adjustable brace  16  slides along the thumbscrew  25  when the thumbscrew  25  is loose, and the adjustable brace  16  is pressed between and retained by the top plate  26  and the bottom plate  28  when the thumbscrew  25  is tightened and the bottom plate  28  is drawn up toward the top plate  26 . 
     In a most preferred embodiment, the fixture  10  has a generally round shape, as depicted in FIGS. 1 and 2, with a diameter that is substantially equal to that of a wafer. Typical sizes includes about 100 millimeters, about 150 millimeters, about 200 millimeters, about 250 millimeters, and about 300 millimeters. The benefit of constructing the fixture  10  in one of these sizes and shape is that it can then be loaded into a test station that is designed to hold a wafer of corresponding size. For example, if a fab typically processes 200 millimeter wafers, and has test stations designed to hold 200 millimeter wafers, then the size of the fixture  10  is preferably about 200 millimeters, so that it can be placed in the wafer handling mechanisms of the test stations, and the individual integrated circuit  22  can be tested using the standard test stations and the fixture  10 . 
     Depicted in FIG. 4 is a third embodiment of a fixture  10  according to the present invention. In this embodiment, the supporting brace  12  is smaller than in the embodiment depicted in FIG.  1 . The supporting brace  12  is mounted to the bottom plate  28 , which holds the supporting brace  12  in an immobile position. 
     In the embodiment depicted in FIG. 4, the smaller adjustable brace  16  is slideably mounted between the first guide rail  14   a  and the second guide rail  14   b . The first guide ail  14   a  and the second guide rail  14   b  are in turn mounted to the bottom plate  28 . In this manner, the first guide rail  14   a  and the second guide rail  14   b  are immobile relative to the first direction, and the supporting brace  12  is immobile relative to the first direction. The spring  24  is connected at one end to the adjustable brace  16  and at the other end to the bottom plate  28 . The top of the fixture  10  is open, allowing the circuitry on the front surface of the integrated circuit  22  to be both electrically probed and viewed. The bottom plate  28  forms a central access port  30 , which allows the back surface of the integrated circuit  22  to also be both electrically probed and viewed. 
     In another embodiment depicted in FIG. 5, the supporting brace  12  is immobile in the first direction, and the adjustable brace  16  moves back and forth along the first guide rail  14   a  and the second guide rail  14   b  in the first direction, under the action of spring  24 , as optionally retained by the thumbscrew  25  (not depicted in FIG.  5 ), as described above. However, in the embodiment depicted in FIG. 5, the supporting brace  12  is not immobile in the second direction, which is perpendicular to the first direction and is within the plane containing both the supporting brace  12  and the adjustable brace  16 , as depicted. 
     In the embodiment of FIG. 5, the supporting brace  12  moves back and forth along the third guide rails  14   c  and the fourth guide rail  14   d  in the second direction. In this manner the first jaw piece  18  can be disposed at a position that is skewed from the travel of the second jaw piece  20  along the first direction. In this manner the fixture  10  can accommodate integrated circuits  22  that are not square. As depicted in FIG. 5, the supporting brace  12  and the adjustable brace  16  are not touching the guide rails  14   a - 14   d . However, this is only done for convenience in depicting and understanding the separate pieces of the embodiment. In actual construction the supporting brace  12  and the adjustable brace  16  engage the guide rails  14   a - 14   d.    
     As depicted, the supporting brace  12  and the adjustable brace  16  are mounted within a single bottom plate  28 . However, in other embodiments the supporting brace  12  and the adjustable brace  16  are mounted within a plate that is sandwiched between a bottom plate  28  and a top plate  26 , similar to the embodiments of FIGS. 2 and 3, except that in those embodiments the middle plate of the embodiment of FIG. 5 is replaced with a different form of the supporting brace  12  that performs many similar functions. 
     Many of the elements described above can be applied to the embodiment of FIG.  5 . For example, springs  24  can be placed at either end of the supporting brace  12  along the second direction (not depicted in FIG.  5 ). By having springs  24  on both ends of the supporting brace  12 , the supporting brace  12  tends to be self centering in the second direction, which is a third orientation, and is configured by default for a square integrated circuit  22 . A thumbscrew  25  can also be added to the supporting brace  12  of FIG. 5 (not depicted), which allows the supporting brace  12  to be positioned along the second direction and then retained in the selected position along the second direction. This may be accomplished in the same manner as depicted for the adjustable brace  16  in FIG.  2 . The thumbscrew  25  provides similar benefits to the supporting brace  12  as described above for the adjustable brace  16 . 
     It is appreciated that the invention as described above comprehends numerous adaptations, rearrangements, and substitutions of parts, all of which are considered to be within the scope and spirit of the invention as described, and that the scope of the invention is only to be restricted by the language of the claims given below.