Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2002-11-21
2004-07-20
Pert, Evan (Department: 2829)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S1540PB
Reexamination Certificate
active
06765397
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to electrical components packaged in land grid array (LGA) modules, and more particularly to an apparatus and method for performing electrical testing of LGA modules.
BACKGROUND OF THE INVENTION
The actual working elements of modern electronic and electrical devices often take the form of small electronic chips, that are mounted individually, or with other chips, inside of a module having a closed housing that protects the chips from environmental damage, and provides input/output connections to a circuit incorporating the module.
One commonly used type of module, known as a land grid array (LGA) module, is shown in
FIGS. 1A and 1B
. The LGA module
10
of
FIGS. 1A and 1B
includes a housing, having a substrate
12
and a cover
18
. The substrate
12
has an upper surface for receiving the chips, and a bottom, flat, planar surface
14
having plurality of LGA electrical contacts
16
arranged in an array as shown in FIG.
1
B. Such LGA modules
10
may include more than one thousand LGA electrical contacts
16
. The top of the substrate
12
is closed, or “capped” by joining the cover
18
to the substrate
12
with an adhesive or solder. The cover
18
includes recesses for the chips on the side of the cover
19
joined to the substrate
12
Such LGA modules
10
are typically connected to a circuit card having an array of electrical contacts corresponding to at least a portion of the LGA electrical contacts, by positioning a device known as an interposer
20
, as shown in
FIGS. 2A and 2B
, between the LGA module
10
and the circuit card, and clamping the LGA module
10
and interposer
20
to the circuit card. There are several types of interposers
20
that are typically used for this purpose.
One commonly used type of interposer
20
includes a molded body having a raised frame
19
surrounding a flat planar surface
21
that includes an array of through holes
22
. The through holes
22
are aligned with the arrays of LGA electrical contacts
16
on the LGA module
10
and circuit card, and with respect to a pair of location holes
26
passing through the raised frame
29
. As shown in
FIG. 2B
, each hole
22
in the interposer
20
includes a compressible electrically conductive element
24
, such as a pad of kinked small diameter wire, a C-spring that is compressed when the LGA module
10
is clamped to the circuit card, to provide electrical contact between the LGA electrical contacts
16
and the circuit card.
In a second type of commonly used interposer
20
, the flat planar surface
21
of the interposer
20
is provided by a thin sheet of electrically insulative material, such as a polyimide, that is attached to the raised frame
19
. The sheet of polyimide material includes through holes
22
aligned with the arrays of LGA electrical contacts
16
on the LGA module
10
and circuit card, and with respect to a pair of location holes
26
passing through the raised frame
29
, in the same manner as described above with respect to an interposer
20
having a molded body. In the second type of interposer, however, each hole includes a compressible electrically conductive element
24
formed from a conductive elastomeric material, such as a silver-filled silicone.
The clamping force for holding the LGA module
10
against the circuit card is typically provided by a clamping device having a number of metal plates, stiffeners, tension posts, and a spring element, all held together by one or more screws, in a relationship that applies a clamping force to the LGA module
10
. The clamping device may also include a heat exchanger for dissipating heat generated during operation of the LGA module. These clamping devices are often complex in nature to ensure that the clamping pressure is applied uniformly to the LGA module
10
, for optimal electrical contact with the circuit card and optimal thermal transfer to the heat exchanger.
The electrical performance of LGA modules varies somewhat from module to module, due to slight variations in the performance of the chips, and factors relating to the installation of the chips in the modules that cannot be controlled during fabrication of the module. As is the case in many electronic components, an initial burn in period is also required in some instances to screen out certain defective modules and ensure that the completed modules will not fail prematurely. As a result, it is often necessary to test completed LGA modules prior to installing them into a circuit to determine their individual performance, or to burn in the modules at various operating voltages, clock speeds, and power levels, while the module is operating in a known temperature range.
It is desirable that an apparatus and method for testing the LGA modules be capable of closely emulating the physical mounting arrangement that will be used for attaching the LGA module to a circuit card during actual use of the module. While it would appear to be desirable to utilize the actual clamping hardware for testing the module, i.e. the hardware that will be used for mounting the LGA module on a circuit card in an electronic device, such hardware is typically not capable of being conveniently and repeatedly installed and removed in the manner that would be required for the mounting hardware to function as a test apparatus. Such hardware is typically designed to be so compact and light weight that it does not lend itself well to repeatedly establishing clamping and electrical connection conditions that are uniform enough, from module to module, to serve as a basis for testing.
In addition, a typical set of clamping hardware does not include a heat exchanging device that is sophisticated enough to allow testing of the module under a variety of environmental temperature conditions. The heat sinks used in such clamping arrangements are generally designed to operate only in the specific application and operating environment that the module will encounter during actual operation, and do not allow the module to be tested at higher or lower operating temperatures.
In a test apparatus, it is highly desirable to rapidly apply a clamping force to the cover
18
of the LGA module during testing, for clamping the LGA module against a circuit card, with a device such as an air or hydraulic cylinder or an arbor press, having a ram element that can be quickly moved along a one dimensional axis. Unfortunately, the upper surface of the cover
18
is typically not parallel to the bottom, flat, planar surface
14
of LGA module and the electrical contacts
16
. If a one dimensional force is applied directly to the cover
18
, using the ram element, the LGA electrical contacts
16
will not be clamped with uniform force against the circuit card. If the contacts
16
are not clamped with a uniform force, the electrical conductivity of the contacts
16
will not be uniform or representative of what will be achieved in service, thereby introducing an unacceptable variable into the test results. Also, if the upper surface of the cover
18
is tilted slightly with respect to the lower surface of the LGA module
10
, good thermal contact will not be achieved between a heat exchanger clamped against the cover
18
by the ram element, thereby making it difficult to precisely control temperature of the LGA module
10
during testing and burn-in of the module.
What is needed is an apparatus and method for effectively and efficiently testing and burning-in LGA modules.
SUMMARY OF THE INVENTION
Our invention provides an apparatus and method for effectively and efficiently testing land grid array (LGA) modules in a mounting arrangement that closely matches the actual mounting arrangement that will be used for attaching the LGA modules to a circuit card, through the use of a self-aligning clamping device for clamping the LGA against a circuit card. The self-aligning clamping device includes a clamping body having an LGA contact surface adapted for bearing against the LGA module, and a pivot element for receiving a clamping force from a ram element sele
Corbin, Jr. John S.
Garza Jose A.
Mahaney, Jr. Howard V.
Cardinal Law Group
International Business Machines - Corporation
Nguyen Tung X.
Salys Casimer K.
LandOfFree
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