Abstract:
A method of using a socket to electrically interconnect a microelectronic assembly having electrically conductive joining units and a substrate having electrically conductive contacts includes providing a socket having a plurality of apertures with deflectable, resilient lip regions, and positioning the socket over the substrate so that the plurality of apertures are in substantial alignment with at least some of the electrically conductive contacts of the substrate. The microelectronic assembly is then juxtaposed with the substrate so that the socket is between the microelectronic assembly and the substrate and so that the joining units of the microelectronic assembly confront the contacts of the substrate. The joining units of the microelectronic assembly are then inserted into the apertures of the socket so that the conductive joining units deflect the deflectable lip regions of the socket for allowing the plurality of joining units to pass through each aperture, whereby the conductive joining units of the microelectronic assembly are held in electrical contact with the contacts of the substrate by the resilience of the deflectable lip regions contacting the conductive joining units.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 09/363,496 filed Jul. 29, 1999, now U.S. Pat. No. 6,126,455 which, in turn, is a continuation of U.S. patent application Ser. No. 09/112,545 filed Jul. 9, 1998, now U.S. Pat. No. 5,951,305. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to sockets for use in connecting semiconductor chip assemblies to substrates and the methods of making such sockets. 
     2. Description of the Related Art 
     U.S. patent application Ser. No. 08/254,991 filed on Jun. 7, 1994, the disclosure of which is incorporated herein, discloses a connector for mounting a microelectronic element to a substrate. In certain embodiments, the connector includes a sheet-like dielectric body having a plurality of holes, an array of resilient contacts secured to the dielectric body and an array of terminals electrically connected to the contacts. 
     U.S. Pat. No. 5,632,631, which issued on May 27, 1997, the disclosure of which is incorporated herein, discloses, in certain embodiments, a contact comprising a base portion and a plurality of asperities protruding upwardly from the surface of the base portion. The base portion may include a ring-like anchor region and a plurality of tabs extending inwardly from the anchor region to a common center. The asperities may be disposed on the tabs. The &#39;631 patent also discloses a connector which includes a connector body and at least one of the contacts described above and wherein the anchor region of each contact is fixed to the connector body and the tabs are free to bend. When a mating contact element (such as a lead or solder ball) is forced against the contact, the tabs bend and the mating contact element is wiped across the asperity causing the sharp edges of the asperity to scrape the mating contacting element so that an electrical connection to the mating contact element can more easily be made. 
     U.S. Pat. No. 5,615,824, which issued on Apr. 1, 1997, the disclosure of which is incorporated herein, discloses a method of making an electrical connection. In a preferred embodiments, the method comprises the steps of engaging a first element having a plurality of solder masses and a second element having a plurality of resilient contacts; heating the elements so that the contacts penetrate the solder masses; and cooling the assembly. The second element may be comprised of a connector body having a plurality of holes. Each resilient contact may have one or more tabs which project over one of such holes. The tabs bend during the engaging step and spring back as the contacts penetrate the solder masses. Each contact may be covered by a solder mask made of a dielectric material that is a thermoplastic. 
     Certain embodiments disclosed in U.S. patent application Ser. No. 08/862,151, filed on May 22, 1997 disclose a connector for a microelectronic assembly which includes a sheetlike body having a plurality of contacts, a substrate having leads, and a support structure extending between sheetlike element and the substrate. The contacts may include several sheetlike metallic projections extending inwardly around a hole in the sheetlike element one side of the sheetlike element. A support structure, such as an array of non-collapsing structural posts is on another side of the sheetlike element. Each of the contacts is surrounded by several posts. The posts keep the sheetlike element spaced away from a substrate to which the posts are attached. The disclosure of the &#39;151 application is incorporated herein. 
     Many of the sockets described in the disclosures set for above as well as many other sockets of the prior art rely upon pressure to maintain an electrical contact between the device to be tested and the contacts of the socket. A lid or other backing element is placed over the device and pressure is applied to the lid to insure that the electrical contact between the device and the contacts on the socket are maintained. Some sockets may, in the alternative or in addition, have a mechanism for engaging the sides of the chip or the device. While the above mentioned socket designs are important improvements to socket technology, further improvements are desirable. 
     SUMMARY OF THE INVENTION 
     The present invention relates to methods of using sockets for connecting a semiconductor chip assembly to an external substrate such as a printed circuit board. Such semiconductor chip assemblies have a plurality of electrically conductive joining units such as bumped leads or ball leads. Semiconductor chip assemblies which may be connected to an external substrate using the socket of the present invention include, for example, flip chip assemblies, ball grid arrays and assemblies, such as those disclosed in commonly assigned U.S. Pat. Nos. 5,148,265 and 5,148,266. The semiconductor chip assembly may comprise a single semiconductor chip, a plurality of semiconductor chips or wafer. The socket of the present invention can be used to permanently connect a semiconductor chip assembly to an external substrate, such as a printed circuit board; or to temporarily connect such an assembly to an external substrate, such as a test circuit board, for testing purposes. The socket of the present invention incorporates a grabbing or locking feature that is capable of capturing the joining units of the chip assembly. In certain embodiments, the socket of the present invention is lidless because it does not require a lid or any other mechanism for applying pressure to a semiconductor chip assembly in order to maintain an electrical contact between the terminals of the chip assembly and the socket. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a socket according to one embodiment of the present invention. 
     FIG. 1A is a top view of a portion of a socket according to another embodiment of the present invention. 
     FIG. 1B is a top view of a portion of a socket according to another embodiment of the present invention. 
     FIG. 1C is a top view of a portion of a socket according to another embodiment of the present invention. 
     FIG. 1D is a bottom view of the socket depicted in FIG.  1 A. 
     FIG. 1E is a bottom view of the socket depicted in FIG.  1 B. 
     FIG. 1F is a bottom view of the socket depicted in FIG.  1 C. 
     FIG. 2 is a side view of the socket of FIG. 1 shown in conjunction with a semiconductor chip assembly and an external substrate. 
     FIG. 3 is a side view of the another embodiment of the socket of the present invention in conjunction with a semiconductor chip assembly and an external substrate. 
     FIG. 4 is a side view of a socket according to another embodiment of the present invention in conjunction with a semiconductor chip assembly and an external substrate. 
     FIG. 5 is a side view of a socket according to another embodiment of the present invention in conjunction with a semiconductor chip assembly and a printed circuit board. 
     FIG. 6 is a side view of a socket according to another embodiment of the present invention in conjunction with a semiconductor chip assembly  10  and an external substrate  14 . 
     FIG. 7A is an exploded perspective view of a portion of a socket according to another embodiment of the present invention. 
     FIG. 7B is a perspective view of the socket of FIG.  7 A. 
     FIG. 7C is a bottom view of the socket of FIG.  7 B. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention relates to methods of using sockets for connecting a semiconductor chip assembly having a plurality of electrically conductive joining units to an external substrate. The socket of the present invention incorporates a grabbing or locking feature that is capable of capturing the joining units of the chip assembly when such joining unit is inserted into an aperture in the socket. A portion of a socket according to one embodiment of the present invention is depicted in FIG.  1 . Socket  1  includes a flexible dielectric element  2  having a plurality of apertures  3  and a backing element  5  disposed beneath flexible dielectric element  2 . Backing element  5  has a plurality of holes  6 . Each hole is aligned with one of the apertures in the flexible dielectric element. Backing element  5  also has a first surface  11 , and a second surface  12  opposite the first surface. Holes  6  extend from the first surface  11  to the second surface  12 . Surrounding each aperture  3  is a lip  15 . By the term “lip” it is meant the area immediately adjacent to and surrounding an aperture. Each lip  15  is that portion of flexible element  2  that overhangs the hole  6  which is disposed under an aperture  3 . The socket may also comprise a plurality of spacers  9  disposed beneath backing element  5 . In preferred embodiments, the alpha surfaces of spacers  9  are connected to the backing element  5 . Spacers  9  may be adapted to join the socket to an external substrate and may be comprised of a rigid, semi-rigid or compliant material. FIG. 2 depicts the socket of FIG. 1 in conjunction with a semiconductor chip assembly and an external substrate. 
     As depicted in FIG. 1, flexible dielectric element  2  has a top surface and a bottom surface opposite the top surface. Each of the plurality of apertures extends from the top surface to the bottom surface. Each lip  15  is preferably integral with flexible dielectric element  2 . In preferred embodiments, the top surface of each lip is co-planar with the top surface of flexible dielectric element and the bottom surface of each lip is co-planar with the bottom surface of the flexible dielectric element. The aperture may have any shape, including circular, semicircular, triangular, square, rectangular, or any other geometric or arbitrary shape for capturing a joining unit of a semiconductor chip assembly. For example, FIGS. 1A,  1 B, and  1 C show top plan views of portions of sockets according to various embodiments of the present invention. The apertures depicted in FIG. 1A are circular. The apertures in FIG. 1B are square and the apertures of FIG. 1C have various shapes. In FIG. 1C, aperture  3   a  has a triangular cross-sectional shape. Apertures  3   b  and  3   c  have finger-like projections that extend radially. In other words, the region of the flexible dielectric element that defines each aperture includes a plurality of finger-like projections, the tips of which extend inwardly towards a common center. Such finger-like projections are preferred because they allow the lip of each aperture to more easily deflect so that a solder ball can pass through the aperture. In preferred embodiments, all the apertures in a socket are uniform. 
     The effective diameter of each aperture in the flexible dielectric element should be smaller than the diameter of the electrically conductive joining unit that will be inserted into the aperture. For example, if the joining unit is a solder ball, the effective diameter of the aperture should be less than the diameter of the solder ball. By the term “effective diameter” we mean the diameter of the largest circle which will fit within the aperture without touching the sides of the aperture. In preferred embodiments, the geometric center of this circle will be generally aligned with the geometric center of the aperture. In preferred embodiments, the effective diameter of each aperture is from 1 to 10 mils smaller, more preferably, 3 to 5 mils smaller, than the diameter of the electrically conductive joining unit that will be inserted into the aperture. Although the apertures may be randomly arranged, in preferred embodiments, apertures  3  are arranged in a grid-like array and have a constant center-center distance, or pitch, of 250 μm to 1500 μm. 
     The first surface  11  of backing element  5  is connected to the bottom surface of flexible dielectric element  2 . Each of the holes  6  should be aligned with one of the apertures  3 . Just as each aperture maybe any shape, each hole may also be any share. For example FIGS. 1D,  1 E, and  1 F show bottom plan views of portions of sockets according to various embodiments of the present invention. The holes  6 , as well as the apertures  3 , depicted in FIG. 1D are circular. In FIG. 1E, both the holes  6  and the apertures  3  are square. In FIG. 1F, the shapes of hole  6   a  and aperture  3   a  are triangular. Holes  6   b  and  6   c , and apertures  3   b  and  3   c , have finger-like projections that extend radially. It is not necessary that a hole and the aligned aperture have the same shape. For example, in FIG. 1F, holes  6   d ,  6   e  and  6   f  are circular while aperture  3   d  is triangular, and apertures  3   e  and  3   f  have finger-like projections. Each aperture will normally be smaller than the aligned hole. 
     In preferred embodiments, the shape of each hole is circular. The diameter of each hole should be larger than the diameter of the electrically conductive joining unit that will be inserted through the aperture and the aligned hole. If the diameter of the hole is too large, then the backing element may not provide sufficient support for the flexible dielectric element and the entire flexible dielectric element will tend to deflect, rather than just the lip portion, when the joining unit is pressed against the flexible dielectric element. If the diameter of hole  6  is too small in relation aperture  3 , the lips may not be flexible enough to deflect to allow the joining units to penetrate the apertures. Because the holes are larger than the joining units, the socket can accommodate semiconductor ship assemblies having some misalignment in joining unit placement and some variation in joining unit size. In preferred embodiments, the diameter of each hole is 1 to 10 mils larger, more preferably 3 to 5 mils larger, than the diameter of the electrically conductive joining unit that will be inserted into the hole. In preferred embodiments, the electrically conductive joining unit will be a solder ball, a solid core solder ball or a bumped lead. Such electrically conductive joining units typically have diameters of 5 to 50 mils. In preferred embodiments, such joining units have diameters of 10 to 30 mils. The size of lips  15  and the flexibility of the flexible dielectric element may be varied to modify the lip resistance to an inserted joining unit. 
     Each of the plurality of spacers  9  has an alpha surface  18 , and a beta surface  19  opposite the alpha surface. The alpha surface  19  is disposed beneath the second surface  12  of the backing element  5 . In preferred embodiments, alpha surface  18  is adhered to second surface  12  of backing element  5 . In order to provide additional support for flexible dielectric element  2 , to allow each lip region  15  to deflect, and to minimize deflection of the rest of the flexible dielectric element, each spacer  9  is preferably located adjacent to one of the apertures but outside the lip region. The spacer may be comprised of a conductive or non-conductive material. If the spacer is comprised of a conductive material, it may be referred to hereinafter as an electrically conductive post. In preferred embodiments, the spacer is comprised of a compliant material. Preferred compliant materials include silicone gels, silicone elastomers and flexiblized epoxies. The plurality of spacers or plurality of electrically conductive posts may be replaced with a sheet or slab of material having a plurality of voids that are aligned with the apertures and holes. Alternatively, each spacer or electrically conductive post may be comprised of a solder ball or a solid core solder ball. In addition to serving as an electrical interconnection between the socket and an external substrate, the posts may also provide additional structural support for the apertures in the flexible dielectric element. In preferred embodiments of the socket of the present invention, the socket includes a plurality of electrically conductive posts that are disposed near the apertures in the flexible dielectric element. When a bumped lead or a solder ball is pressed against each aperture, the posts allow the lips of the flexible dielectric element to deflect but minimize the deflection in the rest of the dielectric element. If the entire flexible dielectric element deflected, the solder ball or bumped lead would be less likely to penetrate the aperture. 
     The socket of this embodiment of the present invention may be used in conjunction with an external circuit  14  having a plurality of electrically conductive contacts  4 . FIG. 2 depicts the socket of FIG. 1 in conjunction with a semiconductor chip assembly and an external substrate. Semiconductor chip assembly  10  may be any type of assembly having a plurality of electrically conductive joining units  13 . Semiconductor chip assembly  10  may be, for example, a flip chip assembly, a ball grid array package or any similar assembly. The joining units may be; for example, bumped leads, solid core solder balls, or solder balls. The joining units  13  depicted in FIG. 2 are solder balls. The beta surfaces  19  of spacers  9  are juxtaposed to the top surface of external substrate  14 . Beta surfaces  19  may be adhered or otherwise connected to the top surface of external substrate  14 . External substrate  14  has a plurality of electrically conductive contacts  4  disposed on it top surface. The contacts  4  should be aligned with the apertures  3  of the flexible dielectric element  2  and the holes  6  of the backing element  5 . External substrate  14  may be comprised of a rigid or compliant material. A temporary electrical connection between a semiconductor chip assembly  10  and a text circuit board may be made using the socket of the present invention, if, for example, external substrate  15  is a test circuit. A permanent electrical connection between a semiconductor chip assembly  10  and a printed circuit board may also be made using the socket of the present invention, if for example, the external substrate  14  is a printed circuit board. 
     If a temporary electrical connection is made, the socket of the present embodiment of the invention is juxtaposed or connected to a test circuit having a plurality of electrically conductive contacts. The beta surfaces  19  of each spacer  9  are juxtaposed with, or preferably connected to, the test circuit  14 . A semiconductor chip assembly  10  having a plurality of electrically conductive joining units  13  such as solder balls is inserted into the socket. Each solder ball  13  presses against a lip region  15  of the flexible dielectric element  2 . The backing element  5  and spacer  9  support the flexible dielectric element  2  and minimize its deflection, except in the lip regions. Each lip region deflects and allows the solder ball  13  to penetrate into and pass through each aperture  3 . Once the largest cross-sectional portion or the “equator” of the solder ball  13  passes the tip of each lip region, the lip region springs back. The solder ball  13  penetrates into and through the hole  6  in the backing element  5  and is locked into place by the resilience of the lip region engaging the solder ball on one side and the engagement of the solder ball and a contact surface on the opposite side. The solder ball touches a contact on the test circuit and is thereby electrically interconnected to the test circuit. The semiconductor chip assembly can then be electrically tested. The testing procedure may take less than a second or may be extended for days or weeks or even longer. Extended testing frequently includes thermal cycling. The flexibility of the socket allows it to compensate for differences in the temperature-induced expansion and contraction of the components of the semiconductor chip assembly and the test circuit that will occur in such thermal cycling. The semiconductor chip assembly is then removed from the socket. Another semiconductor chip assembly may then be tested using the socket and test circuit. 
     To make a permanent connection, the socket described above is connected to a printed circuit board such that the beta surfaces  19  of the spacers  9  are connected to a printed circuit board or other circuitized external substrate. The semiconductor chip assembly is inserted into the socket as described above. The electrically conductive joining units of the chip assembly are reflowed to bond the joining units to the printed circuit board. The chip assembly may be tested prior to the reflow step to insure that the semiconductor chip assembly is functioning properly. If the semiconductor chip assembly is defective, it can be removed from the printed circuit board and another semiconductor chip assembly can be connected to the printed circuit board using the same socket. 
     In preferred embodiments of the present invention, the height of each spacer is uniform. The height of each spacer, as measured from the alpha surface to the beta surface, plus the height of the flexible dielectric layer and the backing element should be about equal to the height of the one electrically conductive joining unit plus the height of the contact disposed on the external circuit. 
     FIG. 3 depicts a socket of another embodiment of the present invention in conjunction with a semiconductor chip assembly  10  and an external substrate  14 . In the socket depicted in FIG. 3, the compliant spacers have been replaced with a plurality of electrically conductive posts  9 , and each post  9  is a solder mass, such as a solder ball. Each solder mass  9  has an alpha surface  18 , which is connected to the backing element  5 , and a beta surface  19  opposite the alpha surface. External substrate  14  has a plurality of electrically conductive contacts  4  disposed on its top surface. Semiconductor chip assembly  10  has a plurality of electrically conductive joining units  13 . Each of the electrically conductive joining units  13  is aligned with one of the apertures  3  of flexible dielectric element  2 . The joining units depicted in FIG. 3 are solder balls. Each solder ball  13  has an equator  16 . The equator is that section of the solder ball  13  having the largest circumference. In order to test semiconductor chip assembly  10 , or to connect assembly  10  to external substrate  14 , assembly  10  is pressed against socket  1  such that each solder ball  13  is forced against one of the apertures  3 . The lips  15  of each aperture  3  are deflectable and allow the solder ball  13  to penetrate and pass through the aperture  3  and then the underlying hole  6 . As the equator  16  of each solder ball  13  passes through one of the apertures  3 , each lip  15  deflects back into its original position. 
     In another embodiment of the present invention, and as depicted in FIG. 4, the socket of the present invention may also include a plurality of electrically conductive contacts. FIG. 4 depicts a socket in conjunction with a semiconductor chip assembly  10  and an external substrate  14 . The socket comprises a flexible dielectric element  2  having a plurality of apertures  3 . A backing element  5  is disposed beneath the flexible dielectric element  2 . Backing element  5  has a first surface  11 , a second surface  12  opposite first surface  11  and a plurality of holes  6  extending from the first surface  11  to the second surface  12 . Holes  6  are aligned with apertures  3 . Socket  1  also has a plurality of electrically conductive contacts  4  disposed on the second surface  12  of backing element  5 . Semiconductor chip  10  has a plurality of electrically conductive joining units  13 . The beta surfaces  19  of spacers  9  are connected to the top surface of the external substrate  14 . Each of the spacers  9  depicted in FIG. 4 includes a solid core solder ball. 
     Flexible dielectric element  2  has a top surface, a bottom surface opposite the top surface, a plurality of apertures  3  that extend from the top surface to the bottom surface, and a lip  15  surrounding each aperture. Such apertures and lips are described above. The apertures are aligned with the solder balls or bumps  13  which are disposed on the semiconductor chip assembly to be tested using the socket. The effective diameter of each aperture is slightly smaller than the diameter of the solder ball, preferably 1 to 10 mils smaller, more preferably 3 to 5 mils smaller. The backing element  5  has a first surface  11 , a second surface  12  opposite the first surface and a plurality of holes  6  that extend from the first surface to the second surface. The first surface of the backing element is disposed under the bottom surface of the flexible dielectric element. In preferred embodiments, the first surface of the backing element is laminated to the bottom surface of the flexible dielectric element. Each hole  6  is aligned with one of the apertures  3 . The diameter of each hole is larger than the diameter of the aligned aperture. The diameter of each hole is larger than the diameter of the joining unit which will be inserted into the hole and aligned aperture. In preferred embodiments, the effective diameter of each hole  6  is 1 to 10 mils larger, preferably 3 to 5 mils larger, than the diameter of solder ball  13 . The lip of each aperture must be deflectable to the extent that when a solder ball is pressed against the aperture, the lip will deflect inwardly (toward the backing element) and will allow the solder ball to penetrate through the aperture. After a significant portion of the solder ball has penetrated the aperture, the lip will tend to rebound back to its original orientation, thus locking the solder ball into place. The solder ball or bumped lead is thereby captured by the socket and it is unlikely that the solder ball or bumped lead will be inadvertently displaced from the socket. The lip tends to rebound once the “equator” of the solder ball has penetrated the aperture. The equator of the solder ball is typically about halfway between the top and bottom of the solder ball. Each aperture and each hole may be any shape. As mentioned above, in preferred embodiments, the region of the flexible dielectric element that defines each aperture includes a plurality of finger-like projections, the tips of which extend inwardly towards a common center. One reason such apertures are preferred is because such finger-like projections form relief zones which facilitate the deflection of the lips when a solder ball is pressed against an aperture. In preferred embodiments of the present invention, the flexible dielectric element has a plurality of aperture defining regions each of which includes at least one relief zone. 
     The cross sectional area of each of the holes of the backing element may take any shape, including any of the shapes listed for the apertures. The general shape of each hole may be the same as, similar to or different from the shape of the aligned aperture. In preferred embodiments, the cross-sectional area of each hole is circular. Each contact should be positioned such that an electrical connection can be made between solder ball  13  and contact  4 . Preferably, contact  4  wipes against solder ball  13  as it penetrates aperture  3  and hole  6 . Although the present invention is not limited by any theory of operation, it is believed that the wiping action tends to rupture the film or layer of oxide which may be present on the surface of the solder ball and thus facilitates an electrical connection between the contact and the solder ball. In preferred embodiments, each aperture has a central opening and is disposed on the backing element such that the central opening is aligned with one of the holes  6  and apertures  3 . Each central opening should be sized and shaped to allow a solder ball  13  to penetrate such central opening and wipes against the surface of such solder ball. The shape of each central opening is preferably similar to, and more preferably co-extensive with, the aligned aperture  3 . 
     In preferred embodiments the flexible dielectric element is from 25 to 100 μm thick. The flexible dielectric element is preferably comprised of polyimide. The backing element may be comprised of a flexible or a rigid material. In preferred embodiments, the backing element is comprised of a material selected from the group consisting of FR-4, plastics, polyimide and dielectric coated metals. If the socket of the present invention comprises contacts which are disposed on the flexible dielectric element or the backing element, the spacers  9  should be electrically conductive. Such electrically conductive spacers may be comprised of, for example, solid core solder balls, solder balls, or an electrically conductive elastomeric material such as an electrically conductive silicone or epoxy. 
     The electrically conductive contacts may be disposed on the top and bottom surfaces of the flexible dielectric element; the second surface of the backing element; or the second surface of the backing element and at least one of the top and bottom surfaces of the flexible dielectric element. In preferred embodiments, the contacts are disposed on at least the second surface of the backing element. If the contacts are disposed on the top surfaces of the flexible dielectric element, contacts should also be disposed on the bottom surface to insure that the electrical connection can be maintained as the joining units penetrates the aperture, and vice versa. In preferred embodiments, the contacts are comprised of gold, copper, alloys thereof, or combinations thereof. The contacts are preferably 10 to 100, more preferably 10 to 50, microns thick. Each electrically conductive contact has a chip-assembly-end and a substrate-end. If the contact is disposed on the flexible dielectric element, the chip-assembly-end of each contact should be disposed adjacent to the aperture such that the contact will wipe against the solder ball when it is pressed into the aperture. If the contact is disposed on the backing element, the chip-assembly-end of each contact should be disposed at or over each hole such that the contact will wipe against the solder ball when it is pressed through the aperture and the hole. The substrate-end of each contact must be adapted to connect to an external substrate. 
     FIG. 5 depicts a socket of another embodiment of the present invention in conjunction with a semiconductor chip assembly  10  and a printed circuit board  14 . The socket of FIG. 5 is similar to the socket of FIG. 4 except that the socket of FIG. 5 does not have a plurality of spacers disposed beneath the contacts  4 . The printed circuit board  14  has a plurality of depressions  22 , each of which is aligned with one of the solder balls  13 . Board  14  also has a plurality of electrically conductive contact pads  21  disposed on it top surface. Each contact  4  is may be electrically interconnected to one of the contact pads  21 . Each contact  4  may be a ring-like structure disposed around the holes  6  and having a central opening  20 . In preferred embodiments, a portion of each ring-like contact extends beyond the edge of hole  6  and each central opening  20  is co-extensive with the aligned aperture  3 . In particularly preferred embodiments, the ring-like contacts  4  are electrically conductive and are typically comprised of a metal such as copper, gold, alloys thereof or combinations thereof. 
     FIG. 6 depicts a socket according to another embodiment of the present invention in conjunction with a semiconductor chip assembly  10  and an external substrate  14 . The socket of FIG. 6 has a plurality of top contacts  4  disposed on the top surface  23  of flexible dielectric element  2 . The socket also has a plurality of bottom contacts  4 ′ disposed on the bottom surface  24  of flexible dielectric element  2 . Each top contact  4  is electrically connected to one of the bottom contacts  4 ′. Such electrical interconnection may be made, for example, with a plated via extending through flexible dielectric element  2  and backing element  5 . Assembly  10  has a plurality of electrically conductive joining units  13 . Each conductive post  9  is electrically connected to a circuit disposed on external substrate  14 . 
     In an alternative embodiment, portions of each contact  4  may be disposed on the top surface, the bottom surface and the interior of flexible dielectric element  2 . Portions of such contacts may also be disposed on the first surface, the second surface and/or the interior of backing element  5 . If any portion of contact  4  is disposed on the top surface  23  of flexible dielectric element  2 , an insulative material, such as a solder mask or other dielectric material may need to be disposed between the top surface  23  and the semiconductor chip assembly to avoid a short. 
     FIG. 7A is an exploded perspective view of a portion of a socket of the present invention. FIG. 7A depicts a flexible dielectric element  2  having an aperture  3 . A backing element  5 , having a hole  6 , is disposed beneath the flexible dielectric element  2 . A contact  4  having a central opening  20  is disposed beneath backing element  5 . The geometric centers of aperture  3 , hole  6  and central opening  20  are aligned. Aperture  3  is in the shape of a plurality of finger-like projections extending from a common center. Hole  6  is circular and central opening  20  is in same shape and size as aperture  3 . FIG. 7B depicts a portion of a socket of the present invention wherein the components described above with respect to FIG. 7A are in their normal orientation. Contact  4  is disposed on the second surface of backing element  5  and flexible dielectric element  2  is connected to the first surface of backing element  5 . A socket of the present invention will normally have a plurality of such contacts. A bottom plan view of a portion of such socket having a plurality of contacts is depicted in FIG.  7 C. 
     FIG. 7C is a bottom view of a portion of a socket of the present invention that depicts a preferred configuration for the apertures  3  and contacts  4 . Backing element  5  has a plurality of holes  6 , which extend from its first surface (not shown), to its second surface  12 . A plurality of contacts  4 , each having a central opening  20 , is disposed on the second surface  12 . A flexible dielectric element (not shown), having a plurality of apertures  3 , is disposed on the first surface of the backing element  5 . The geometric center of each central opening  20  is preferably aligned with the geometric center of one of the holes and one of the apertures  3  of backing element  5 . Each aperture is shaped like a plurality of finger-like projections that extend from a common center. The outer periphery of each contact is circular. The central opening of each contact has a shape and a size that is the same as the shape and the size of the aligned aperture. 
     When the socket of the present invention includes electrically conductive posts, such posts may be connected to an external substrate, such as a printed circuit board, to form a testing device or a sub-assembly. If a testing device is formed, a semiconductor chip assembly can be temporarily connected to such connection component to test the electrical properties of the assembly. After testing the semiconductor chip assembly can be permanently connected to the connection component. In preferred embodiments of the testing device, the device includes a plurality of sockets of the present invention so that a plurality of semiconductor chip assemblies can be tested simultaneously. If a sub-assembly is formed, the connection component may be used as an adapter to connect a semiconductor chip assembly having a set of electrically conductive connection points to an external substrate, such as a printed circuit board, having a different arrangement of electrically conductive connection points. In either case, the substrate-end of each contact is connected to one of the electrically conductive posts. 
     As these and other variations and combinations of the features discussed above can be employed, the foregoing description of the preferred embodiments should be taken by way of illustration rather than as limiting the invention.