Electrical connectors – Including elastomeric or nonmetallic conductive portion – Adapted to be sandwiched between preformed panel circuit...
Reexamination Certificate
2001-02-22
2002-07-23
Ta, Tho D. (Department: 2833)
Electrical connectors
Including elastomeric or nonmetallic conductive portion
Adapted to be sandwiched between preformed panel circuit...
C439S066000, C439S071000
Reexamination Certificate
active
06422879
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a socket used for electrically connecting a semiconductor device, i.e., an Integrated Circuit (IC), to the circuit board of a testing apparatus or system and more particularly, to a socket preferably used for a surface-mounting semiconductor device that comprises electrodes arranged in the form of “area array” at the bottom of its package, in which the electrodes at the package bottom are electrically connected to the circuit board.
2. Description of the Related Art
In recent years, the need of the market to provide semiconductor devices (ICs) with multiple function, high-speed operation, and low power consumption has been becoming stronger. According to this need, the package type of semiconductor devices has been changed. Specifically, instead of the conventional Quad Flat Package (QFP) with electrodes arranged at its periphery, the “area array package” with electrodes arranged at its bottom, such as the Ball Grid Array (BGA) and Land Grid Array (LGA), has been becoming popular. With the area array package, electrodes are arranged at the flat bottom of the package in the form of area array.
Generally, on testing the electrical characteristics of the IC chip encapsulated in the package, the packaged semiconductor device is electrically connected to the circuit board of a specific testing apparatus or system by way of a socket. Conventional sockets (i.e., testing sockets) have typically had the structure comprising a punched metal plate and contact pins fixed to the plate. However, to test a semiconductor device with the area array package, the conventional sockets are unable to provide satisfactory electrical characteristics. Thus, various techniques relating to the testing sockets themselves and materials used therefor have been developed and proposed so far.
For example, the Japanese Non-Examined Patent Publication No. 7-287048 published in 1995 discloses an IC socket designed for ICs with the BGA package. This socket comprises an elastic rubber plate and springy contact pins arranged on the surface of the plate two-dimensionally. However, this socket has a problem that the durability is low. Specifically, the contact pins are likely to be deformed with the increasing operation time. As a result, there is a possibility that the electrodes of the IC or semiconductor device do not contact the pins as desired, degrading the reliability.
The Japanese Non-Examined Patent Publication Nos. 9-35789 and 9-161870 published in 1997 disclose an anisotropically conductive sheet applicable to IC sockets. The sheet comprises an elastic rubber body and thin metal wires buried in the sheet, which have an advantage to provide improved contact with the semiconductor device. However, the sheet has a problem that it is unable to cope sufficiently with the miniaturization of the device and pitch narrowing of its electrodes. This is because the metal wires are arranged obliquely to the direction perpendicular to the sheet itself and as a result, it is difficult to decrease the distance between the contact points on the surface of the sheet.
The Japanese Non-Examined Patent Publication No. 5-62727 published in 1993 discloses an anisotropically conductive connection member applicable to mounting an IC chip on a circuit board or a package. This member comprises an elastic rubber sheet and bunches of metal wires buried in the sheet, where these bunches of wires are selectively provided at positions corresponding to the pads or electrodes of the IC chip and the circuit board or package. This member has an advantage that it can be used for test of IC chips with miniaturized and pitch-narrowed pads/electrodes because the wires are fixed perpendicular to the sheet itself. However, this member has the following problem.
Specifically, the bunches of wires disturb the elastic deformation of the rubber sheet and thus, the intrinsic elastic property of the sheet is damaged. Accordingly, if the member is applied to test of IC chips with the BGA package, excessive force tends to be applied to the ball-shaped terminals or electrodes of the chips. This causes a problem that the terminals/electrodes are likely to be damaged.
Moreover, the Japanese Non-Examined Patent Publication No. 11-214594 published in 1999 discloses an anisotropically conductive sheet applicable to test of IC chips. This sheet comprises an elastic rubber body and conductive particles selectively distributed in the sheet at positions corresponding to the pads or electrodes of the IC chip and the circuit board for test. This sheet has an advantage that it can be used for test of area-array packaged IC chips with miniaturized and pitch-narrowed pads/electrodes.
The Japanese Non-Examined Patent Publication No. 10-197599 published in 1998 discloses a test apparatus of semiconductor devices or ICs. This apparatus comprises an anisotropically conductive sheet and an insulating sheet. The insulating sheet has openings at positions corresponding to the pads or electrodes of the IC chip to be tested. In the testing operation, the insulating sheet is placed between the anisotropically conductive sheet and the IC chip in such a way that the pads/electrodes of the chip are engaged with the openings of the insulating sheet, improving the positioning accuracy of the chip. This apparatus can be used for test of area-array packaged IC chips with miniaturized and pitch-narrowed pads/electrodes.
An example of the conventional IC sockets of this type is shown in
FIG. 1
, in which the use of the IC socket is illustrated.
As seen from
FIG. 1
, the conventional IC socket
210
comprises an anisotropically conductive sheet
208
and a frame-shaped package guide
207
surrounding the periphery of the sheet
208
. The sheet
208
is formed by an approximately rectangular, sheet-shaped base material (i.e., body)
204
and conductive particles
203
distributed locally therein. The base material or body)
204
is made of an insulating, elastic rubber. The particles
203
are selectively provided at positions corresponding to the electrodes
206
of a circuit board
205
of a test apparatus (not shown) and the solder balls
201
of a semiconductor device, i.e., IC chip
200
, to be tested. As the base material
204
, silicone rubber or the like may be used. The average diameter of the particles
203
is, for example, several tens micrometers (e.g., 40 &mgr;m).
The package guide
207
, which is made of an insulating material, has the same approximately rectangular plan shape as the sheet
208
. The size of the guide
207
is so designed that the body
202
of the IC chip
200
is fitted into the guide
207
, as shown in FIG.
1
.
When the IC chip
202
is subjected to a test on the test apparatus, the chip
202
is electrically connected to the circuit board
205
by way of the anisotropically conductive sheet
208
. Specifically, first, the chip
202
is inserted into the guide
207
so that the solder balls
201
are placed on the respective conductive regions (in which the conductive particles are distributed) of the sheet
208
, as shown in FIG.
1
. Next, a downward pressure is applied to the body
202
of the chip
200
, thereby pressing the balls
201
toward the sheet
208
and causing deformation of the conductive regions of the sheet
208
. Because of the deformation of the regions, the conductive particles
203
existing in the regions are contacted with each other, forming electrical paths between the balls
201
of the chip
200
and the electrodes
206
of the board
205
. As a result, the balls
201
are electrically connected to the corresponding electrodes
206
.
Typically, to confirm the position of the bottom ends of the solder balls
201
, the bottom ends of the balls
201
may be monitored or checked with a suitable sensor in the test operation. From this point of view, it is necessary that the surfaces of the balls
201
include no or less damages and solder waste.
The conventional IC socket
210
shown in
FIG. 1
has an advantage that the solder balls
201
are
McGinn & Gibb PLLC
Ta Tho D.
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