Test sockets for integrated circuits

A test socket for an integrated circuit includes a frame body, a number of electrical contacts, two sliding plates, a mechanism for slidingly moving the sliding plates in a horizontal direction, and two elastic elements. When applying a force to the mechanism, the sliding plates slide away from each other to make each ball contact of a ball grid array integrated circuit move downwardly into an associated through-hole of the sliding plate. When the force is removed, returning forces provided by the elastic elements return the sliding plates to their close contact status, and each ball contact is born against by an associated electrical contact and thus retained in the associated through-hole of the sliding plate such that signals from the ball contacts can be outputted via the electrical contacts.

BACKGROUND OF THE INVENTION 
 1. Field of the Invention 
 The present invention relates to test sockets for high pin count integrated
 circuit packages, and more particularly to test and burn in sockets for 
 ball grid array integrated circuit packages. 
 2. Description of the Related Art 
 Surface mounted, high pin count integrated circuit packages have been 
 dominated by quad flat packs (QFPS) with various pin configurations. These
 packages have closely spaced leads for making electrical connections 
 distributed along four edges of the flat packages. These packages have 
 become limited by being confined to the edges of the flat pack even 
 through the spacing between the pins is small. 
 A new package, a ball grid array (BGA) has been adopted to meet the 
 requirement of high pin count, in which the electrical contact points are 
 distributed over the entire bottom surface of the packages to overcome the
 problem of insufficient space in the edges for the pins. More contact 
 points can be located with greater spacing than with the QFPS. These 
 contacts are solder balls that facilitate flow soldering of the packages 
 onto a printed circuit board. Thus, BGA's are popular than QFP's. 
 Sockets that accept BGA's are necessary for testing, burn-in, 
 re-programming, and sometimes for production use where the integrated 
 circuit may need replacing. Several such sockets have been developed to 
 satisfy this need, and most of them are of a clam shell design, wherein a 
 hinged top opens to allow package entry, and closing the top retains the 
 package within the socket. The socket includes a bed of contacts spaced to
 match the BGA contacts and a spring load is arranged to press the package 
 onto the bed of contracts to ensure electrical connections. It is, 
 however, found that the socket contacts place forces onto the IC contacts 
 in the same direction. This force drives one side of the package against 
 an abutment of the socket. With a large number of contacts this cumulative
 force of many spring loaded contacts is very large and may physically 
 damage the package. 
 U.S. Pat. No. 5,578,870 to Farnsworth et al. on Nov. 26, 1996 discloses a 
 top loading test socket for ball grid arrays. In said patent, a movable 
 plate is used. The ball contacts are lowered into through-holes in the 
 plate when applying a force to a lever arm to move the plate. A spring 
 means returns the plate to its initial position after the force is 
 removed, such that the electrical contacts that extend through the 
 through-holes of the plate are lowered to bear against the ball contacts 
 to thereby retain the BGA IC in place. In such an improved arrangement, 
 each ball contact is born by a corresponding electrical contact in the 
 same direction, while the other side of the ball contact bears against an 
 edge of the corresponding hole. It is, however, found that the BGA IC is 
 ejected out of the test socket as a result of being subjected to uneven 
 forces if the ball contacts bear the corresponding holes in different 
 relative points (see FIG. 1 of the drawings). In addition, the electrical 
 contacts bear against the ball contacts and thus tend to be damaged in the
 bearing points after a long-term use. 
 U.S. Pat. No. 5,556,293 to Pfaff issued on Sep. 17, 1996 discloses a 
 mounting apparatus for ball grid array device that also uses a plate 
 movable in a direction identical to that disclosed by U.S. Pat. No. 
 5,578,870. Accordingly, the ejection problem of the IC out of the test 
 socket as a result of uneven forces is inevitable. 
 The present invention is intended to provide improved test sockets for 
 integrated circuits that mitigates and/or obviates the above problem. 
 SUMMARY OF THE INVENTION 
 In view of the problem of the prior art, it is a primary object of the 
 present invention to provide a test socket for a ball grid array 
 integrated circuit that is subjected two symmetric forces on both sides, 
 thereby avoiding ejection of the integrated circuit out of the test socket
 as a result of uneven forces. 
 It is another object of the present invention to provide electrical 
 contacts that are in arcuate surface contact with the ball contacts to 
 avoid damage to the ball contacts. 
 It is a further object of the present invention to provide a test socket 
 that allows easy insertion and extraction of the integrated circuit. 
 In order to achieve the above objects, the conventional test socket has 
 been improved by the present invention such that the sliding plate of the 
 conventional test socket is replaced by two symmetric sliding plates, and 
 two elastic elements are symmetrically disposed to two opposite sides of 
 the sliding plates. By means of provision of the mechanism arranged in the
 upper lid and the sliding plates, the sliding plates slide horizontally 
 away from each other when the upper lid is subjected to a downward force. 
 The elastic elements provide returning forces after the downward force is 
 removed. In addition, the electrical contact is designed to have a curved 
 section. The lower section of each electrical contact is inserted into the
 frame body that acts as a base, and the upper curved section of each 
 electrical contact bears against an inner periphery of an associated 
 through-hole of the sliding plate. The upper end of the curved section is 
 arcuate to mate with the ball contact. 
 When the sliding plates move away from each other as a result of an 
 external force, upper ends of the electrical contacts are displaced by the
 sliding plates such that the arcuate section of each electrical contact 
 and the inner periphery of the associated through-hole of the sliding 
 plates together defines a space for receiving an associated ball contact. 
 The ball contact moves downwardly along with the integrated circuit to be 
 tested. The external force is then removed to return the sliding plates to
 their close contact status, while the arcuate section of the upper end of 
 each electrical contact contacts the associated ball contact. Since the 
 sliding plates are symmetrically arranged, the left half electrical 
 contacts and the right half electrical contacts bear against left sides 
 and right sides of the associated ball contacts, respectively. Thus, the 
 integrated circuit to be tested is subjected to even forces to thereby 
 avoid the problem of ejection of the integrated circuit out of the test 
 socket as a result of uneven forces in the prior art. 
 In addition, the upper lid includes an opening having a size the same as 
 that of the integrated circuit to be tested to allow convenient insertion 
 and extraction of the integrated circuit and to restrain horizontal 
 movement of the integrated circuit. 
 Other objects, advantages, and novel features of the invention will become 
 more apparent from the following detailed description when taken in 
 conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
 Referring to FIG. 2, a preferred embodiment of a test socket in accordance 
 with the present invention generally includes a frame body 1, two sliding 
 plates 2, an upper lid 3, a plurality of electrical contacts 4, and two 
 elastic elements 7. 
 The frame body 1 is substantially a base having a plurality of insertion 
 holes 11 defined therein, two fixed slide guide pieces 12, and four posts 
 13. Each insertion hole 11 is located corresponding to a ball contact 6 
 (FIG. 3b) of a ball grid array integrated circuit (BGA IC) (not shown in 
 FIG. 2). 
 The sliding plates 2 are mounted on top of the frame body 1 and each 
 include a plurality of through-holes 21, each through-hole 11 aligning 
 with an associated insertion hole 11 of the frame body 1. Each sliding 
 plate 2 includes a sliding groove 25 in an underside thereof to guide 
 sliding movement of the sliding plate 2 by the associated fixed slide 
 guide piece 12 received in the sliding groove 25. Each sliding plate 2 
 further includes a sliding peg 23 on each lateral side thereof, which will
 be described later. 
 The upper lid 3 is mounted above the sliding plates 2 and includes an 
 opening 31, two downwardly extending lateral plates 32, and four post 
 holes 34. Each lateral plate 32 includes two sliding slots 33. The opening
 31 has a size the same as that of a BGA IC such that the BGA IC may be 
 inserted into the test socket via the opening 31 from top. Inner edges of 
 the opening 31 restrict horizontal position of the BGA IC. Each lateral 
 plate 32 that extends downwardly is outside the associated lateral sides 
 of the sliding plates 2. The sliding grooves 33 in the lateral plates 32 
 extend toward end edges of the lateral plates 32 and respectively receive 
 the sliding pegs 23 of the sliding plates 2 to thereby provide a mechanism
 for moving the sliding plates 2 horizontally and outwardly away from each 
 other. The posts 13 of the frame body 1 extend through the post holes 34 
 of the upper lid 3 to guide vertical movements of the upper lid 3 relative
 to the frame body 1. 
 Each electrical contact 4 is made of conductive metal material and includes
 an upper section 42, a mediate section, and a lower section 41. The lower 
 section 41 of each electrical contact 4 is inserted into and thus retained
 in an associated insertion hole 11 of the frame body 1. The upper section 
 42 of each electrical contact 4 extends through an associated through-hole
 21. The electric contact 4 may be replaced when it is damaged. The upper 
 section 42 of each of the electrical contacts in the left half of the test
 socket is substantially S shaped, while the upper section 42 of each of 
 the electrical contacts in the right half of the test socket is 
 substantially a mirror image of S. 
 Each elastic element 7 is mounted between the frame body 1 and an 
 associated sliding plate 2 and includes a fixing hole 71 so as to be 
 secured to fixing pegs 14 of the frame body 1. The elastic element 7 is 
 made of an arcuate metal plate or any other suitable material. 
 Alternatively, the elastic element 7 may be an elastic member of other 
 shapes, e.g., a spring. When the sliding plates 2 moves away from each 
 other in a horizontal direction, the elastic element 7 is compressed in 
 its mediate portion to generate a returning force between the frame body 1
 and the associated sliding plate 2. 
 When the upper lid 3 is subjected to a downward force, the sliding pegs 23 
 slide along the sliding slots 33 and thus causes the sliding plates 2 to 
 slide away from each other in the horizontal direction under guidance of 
 the fixed slide guide pieces 12 received in the grooves 25. The elastic 
 elements 7 are compressed to generate the returning forces. When the 
 downward force acting on the upper lid 3 is removed, the sliding plates 2 
 move toward and thus contact each other under action of the returning 
 forces of the elastic elements 7. 
 FIGS. 3a and 3b are respectively side view and sectional view of the test 
 socket of FIG. 2 in an assembled status with an IC placed in the test 
 socket for testing. The IC (FIG. 3b) to be tested is placed above the 
 sliding plates 2, and the upper lid 3 is not subjected to a downward force
 such that each sliding peg 23 is in a lower portion of the associated 
 sliding slot 33, as shown in FIG. 3a. The lower section 41 of each 
 electrical contact 4 is fixed in the associated insertion hole 11 of the 
 frame body 1, while the upper section 42 of each electrical contact 4 
 extends upward through the associated through hole 21 such that an upper 
 end of the upper section 42 is in light contact with an associated ball 
 contact 6, as shown in FIG. 3b. 
 FIGS. 4a and 4b illustrate status of the test socket after applying a 
 downward force on the upper lid 3 in FIGS. 3a and 3b. When the upper lid 3
 is pressed downward, the sliding pegs 23 move along the sliding slots 33. 
 Since the pegs 23 are fixed on the sliding plates 2 that cannot move 
 downward, each sliding groove 33 exerts a horizontal force to the 
 associated sliding peg 23 when the sliding peg 23 slides in the sliding 
 groove 33, thereby moving the sliding plates 2 away from each other in the
 horizontal direction. As mentioned above, returning forces are generated 
 by means of compressing the elastic elements 7 during outward movements of
 the sliding plates 2. At the same time, an edge of each through-hole 21 
 bears against a reverse bending point 43 of a lower portion of the "S" 
 section of the associated electrical contact 4. As a result, the reverse 
 bending point 43 and the upper portion of the "S" section of the 
 electrical contact 4 are displaced such that a space (for receiving the 
 ball contact 6) between the edge of the through-hole 21 and the electrical
 contact 4 becomes larger. Each ball contact 6 moves downwardly along with 
 the IC to be tested and partially moves into the associated through-hole 
 21 of the sliding plate 2. It is appreciated that the through-hole 231 
 includes a chambered edge 22 to which the ball contact 6 contacts to 
 thereby avoid damage to the ball contact 6. 
 FIGS. 5a, 5b, and 5c illustrate status of the test socket after removing 
 the downward force acting on the upper lid 3 in FIGS. 4a and 4b, wherein 
 FIG. 5c is an enlarged view of a portion of FIG. 5b. When the downward 
 force acting on the upper lid 3 is removed, as mentioned above, the 
 elastic elements 7 provide returning forces to return the sliding plates 
 2. Thus, the sliding plates 2 carrying the sliding pegs 23 return to 
 positions shown in FIG. 3a, and the upper lid 3 is moved to an initial 
 position before applying the downward force, as shown in FIG. 5a. 
 When the sliding plates 2 return to contact each other, the edge of the 
 through-hole 21 no longer bears against the reverse bending point 43 of 
 the electrical contact 4. As a result, the upper end of the electrical 
 contact 4 springs to its initial position to contact the associated ball 
 contact 6. In this case, the arcuate upper end of the electrical contact 4
 bears against a side of the ball contact 6 to thereby retain the IC to be 
 tested in place. Since the "S" section of each electrical contact 4 in the
 through-holes 21 of one of the sliding plates 2 and the section of mirror 
 image of "S" of each electrical contact 4 in the through-holes 21 in the 
 other sliding plate 2 bear against left side and right side of the 
 associated ball contacts 4, respectively, the overall resultant force 
 acting on the electrical contacts 4 of the IC to be tested is zero. Thus, 
 the ejection problem of the IC out of the test socket as a result of 
 uneven forces is avoided. 
 After testing, the upper lid 3 is pressed downward again to make the 
 electrical contacts 4 and the ball contacts 6 in a status shown in FIG. 
 4b. Then, an extraction means (not shown) is used to extract the IC from 
 the test socket. 
 FIGS. 6a and 6b illustrate a second embodiment of the test socket in 
 accordance with the present invention. The second embodiment is identical 
 to the first embodiment, except for that the sliding grooves 33 of the 
 upper lid 3 and the sliding pegs 23 of the sliding plates 2 have been 
 replaced by a push rod 35 and an operative inclined surface 24 on each 
 sliding plate 2. The push rod 35 is mounted to an underside of the upper 
 lid 3 and includes a conic face 36. Each operative inclined surface 24 is 
 defined in an upper edge of the sliding plate. The operative inclined 
 surfaces 24 together define a conic hole when the sliding plates 2 contact
 each other. The conic face 36 and the operative inclined surfaces 24 may 
 be of other complimentarily formed inclined surfaces, e.g. the conic face 
 36 may be a wedge, and the operative inclined surfaces 24 may be inclined 
 grooves. 
 The push rod 35 is located above the operative inclined surfaces 24, in 
 which the conic face 36 does not contact the operative inclined surfaces 
 24 before the upper lid 3 is subjected to a downward force, as shown in 
 FIG. 6a. When the upper lid 3 is subjected to a downward force, the push 
 rod 35 moves downward into the conic hole defined by the operative 
 inclined surfaces 24. Then, the conic face 36 bears against the operative 
 inclined surfaces 24 and thus exerts a horizontal force to move the 
 sliding plates 2 away from each other, as shown in FIG. 6b. 
 FIGS. 7a and 7b illustrate a third embodiment of the test socket in 
 accordance with the present invention. The third embodiment is identical 
 to the first embodiment and the second embodiment, except for that the 
 mechanism for causing outward horizontal movements of the sliding plates 2
 have been replaced by two inclined pins 37 and 37' on the upper lid 3 and 
 two receiving holes 26 and 26' in the sliding plates 2. The inclined pins 
 37 and 37' are located on two sides of the upper lid 3, respectively. Each
 inclined pin 37, 37' includes an operative inclined surface 38, 38'. The 
 receiving holes 26 and 26' are defined in opposite sides of the sliding 
 plates 2, respectively. Each receiving hole 26, 26' includes an operative 
 inclined surface 27, 27' to cooperate with an associated operative 
 inclined surface 38, 38'. 
 Before the upper lid 3 is subjected to a downward force, the pin 37, 37' is
 partially extended into the associated receiving hole 26, 26' such that 
 the operative inclined surface 38, 38' contacts the operative inclined 
 surface 27, 27', as shown in FIG. 7a. When the upper lid 3 is subjected to
 a downward force, the operative inclined surface 38 and 38' slides along 
 the operative inclined surface 27, 27' to provide a horizontal force for 
 moving the sliding plates 2 away from each other, as shown in FIG. 7b. 
 According to the above description, it is appreciated that the present 
 invention provides two separate sliding plates 2 that can be moved 
 horizontally away from each other by means of sliding mechanism provided 
 between the upper lid 3 and the sliding plates 2 when applying a downward 
 force to the upper lid 3. The forces acting on the BGA IC are symmetric 
 such that the resultant force is zero to avoid uneven single-direction 
 forces acting on the BGA IC in the conventional test socket design that 
 might eject the BGA IC. 
 Although the invention has been explained in relation to its preferred 
 embodiment, it is to be understood that many other possible modifications 
 and variations can be made without departing from the spirit and scope of 
 the invention as hereinafter claimed.