Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1998-08-25
2001-03-20
Karlsen, Ernest (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S755090, C324S758010
Reexamination Certificate
active
06204680
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to test sockets for integrated circuit packages such as a ball grid array package wherein the socket includes an upper housing and a lower housing positioned around a load board and a plurality of solid contact pins extending through the load board from the lower housing and urged into contact with the integrated circuit package by a compliant element in the lower housing for applying independent spring forces to the solid contact pins of the test socket.
BACKGROUND OF THE INVENTION
Testing of integrated circuits contained within ball grid array (BGA) packaging is accomplished through the use of what is commonly referred to in the art as a test socket. BGA test sockets typically include a housing mounted to a load board which interfaces with the test electronics. The load board is generally a circuit board for transferring test signals from the integrated circuit in the BGA to the test electronics.
Previous methods of attaching the test socket to the load board include through hole techniques and surface mounting techniques. In the surface mounting connection, the test socket includes test pads which make contact with the solder balls on the bottom of the BGA as the BGA is compressed against the test pads to transfer the test signals to the load board. A problem associated with the surface mounting test socket arrangement is that the solder balls on the bottom of the BGA can vary in height and good electrical contact between each solder ball and the test pad cannot always be assured. A second problem associated with surface mounting is that once the test pads become contaminated from the solder balls, the entire socket assembly must be replaced.
Through hole techniques for connecting the socket to the load board include holes drilled through the load board for the passage of spring loaded contact pins which contact the solder balls on the BGA and transfer the test signals to the load board through the contact between the test pins and the holes in the load board. A problem associated with the through hole socket arrangement is that the test pins extending up through the load board could easily be bent or damaged which would negatively impact the test results. To avoid this problem, a receptacle can be positioned between the socket and the load board to protect the test pins extending through the load board. The result of incorporating a receptacle requires the length of the test pins in the socket to be increased which creates a problem for testing high speed integrated circuits. To address this problem spring probes have been incorporated which have a short travel length, however with short travel springs, the spring life is short requiring constant replacement. In addition, the use of spring probes in the socket can create an impedance problem for the transfer of the test signal from the BGA to the load board.
Consequently, a need exists for a new test socket for BGA packages which reduces the problems associated with prior art test sockets.
SUMMARY OF THE INVENTION
The present invention provides a newly designed test socket, and particularly a test socket for ball grid array integrated circuit packages which reduces the problems associated with prior test socket arrangements. Although in a preferred embodiment the test socket is designed for use with BGA packages, the socket can also be adapted for use with other integrated circuit packages such as, for example, QFP packages. Briefly, the test socket of the present invention includes an upper housing and a lower housing secured to the top and bottom surfaces respectively of a load board. The load board is a small circuit board which electrically interfaces with the test electronics of an external tester. The upper housing includes a cavity for receipt of the BGA and includes a hole in the lower surface to allow a plurality of solid socket plungers to contact the solder balls on the bottom of the BGA. The socket plungers are positioned within a plurality of channels formed in rows and columns in the lower housing and extend through a plurality of holes also in rows and columns through the load board to contact the solder balls. An elastomeric diaphragm is positioned between the upper surface of the lower housing and the lower surface of the load board and extends over and into the channels in the lower housing below the plungers to provide a spring force to bias the socket plungers upwardly toward the BGA. The flexible diaphragm provides independent spring biased pressure contact for the movable socket plungers mounted in the lower housing. Alternatively and more preferably, springs are positioned in the lower housing below the plungers to bias the plungers. A nonconductive ball is positioned between the plunger and the spring to prevent interference in high frequency applications. In addition, insulator pins can be positioned below the socket plunger and an insulator cap can be positioned above the load board for high frequency applications. Electrically conductive cylindrical eyelets are positioned within the holes in the load board to guide the travel of the socket plungers and to transfer the test signals from the socket plunger to the load board. Alternatively, the through holes in the load board are plated for test signal transfer.
The socket plunger of the present invention eliminates the problems associated with prior BGA test socket arrangements by eliminating the long lead length and spring inductance problems by incorporating a solid socket plunger biased by an elastomeric diaphragm. This arrangement also provides for a long travel length for the plunger to compensate for lack of coplanar solder balls on the BGA. The use of an elastomeric diaphragm also increases the useful life of the test socket when compared to mechanical springs.
For closely spaced test sites, the test socket of the present invention includes a configuration where a hole is cut in the load board and a thinner daughter board is either soldered, connected by a shielded probe, or by a bracket and flexible printed circuit board to the load board. The housing is connected to the daughter board so that the socket plungers can be accommodated in the required closely spaced arrangement. These and other advantages of the present invention will be more clearly understood by reference to the following detailed description.
REFERENCES:
patent: 3016489 (1962-01-01), Briggs et al.
patent: 4232928 (1980-11-01), Wickersham
patent: 4340858 (1982-07-01), Malloy
patent: 5252916 (1993-10-01), Swart
patent: 4401469A1 (1994-07-01), None
patent: 9407823U1 (1994-08-01), None
patent: 19511565A1 (1996-10-01), None
patent: 62-76273 (1987-04-01), None
patent: 6-61321 (1994-03-01), None
patent: 6-88857 (1994-03-01), None
patent: 10-22021 (1998-01-01), None
Green Roy W.
Johnston Charles J.
Sargeant Steve B.
Swart Mark A.
Vinther Gordon A.
Christie Parker & Hale LLP
Delaware Capital Formation Inc.
Karlsen Ernest
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