Electrical connectors – With provision to dissipate – remove – or block the flow of heat – Distinct heat sink
Reexamination Certificate
2003-06-23
2004-06-08
Duverne, Jean F. (Department: 2839)
Electrical connectors
With provision to dissipate, remove, or block the flow of heat
Distinct heat sink
C439S067000
Reexamination Certificate
active
06746270
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to electronic circuit assemblies including land grid array-type devices, and more particularly to biasing assemblies for an electronic circuit assembly that includes a land grid array-type device and a heat sink.
BACKGROUND OF THE INVENTION
Printed circuit boards are generally formed of a rigid dielectric material which is printed with a predetermined pattern of an electrical conductor. Printed circuit boards may be electrically connected to one or more land grid array-type devices such as an application specific integrated circuit (ASIC) or a flexible printed circuit having an array of electrically conductive pads thereon. In order to electrically connect a land grid array-type device to a printed circuit board, an electrical connector or “socket” may be disposed therebetween which has an array of electrically conductive pads on each side thereof. The electrically conductive pads may be constructed from an elastomeric material. The pads on one side of the connector abut with the pads on the land grid array-type device, and the pads on the other side of the connector abut with the electrically conductive array on the printed circuit board.
In order to maintain electrical connection between a land grid array-type device and a printed circuit board, the device and the board must be compressed together, with the electrical connector therebetween. Such an assembly
10
is shown in FIG.
1
. The surfaces
12
,
14
, respectively, of the device
20
(an ASIC being shown in this figure) and the board
22
that the electrical connector
24
is in between must each be flat to within a few mils of an inch. When pads
26
,
28
(shown greatly enlarged for illustrative purposes) on an electrical connector
24
are compressed between a land grid array-type device
20
and a printed circuit board
22
, these pads
26
(especially elastomeric ones) act as miniature springs, exerting forces “F
0
” opposing the compression of the device
20
and the board
22
. Existing large-area connector arrays generate large forces between the printed circuit board and the device being attached to the board. These forces are often large enough to deflect the printed circuit board outside of the flatness requirements. Thus, in addition to needing a relatively large compressive force to maintain contact between the device, the connector and the board, a backing plate
30
,
FIG. 1
, is required to support the printed circuit board
22
and maintain the flatness of the front surface
14
thereof. As shown in
FIG. 1
, such a backing plate
30
is usually positioned on the back side
16
of the printed circuit board
22
, opposite the electrical connector
24
and land grid array-type device
20
. A second backing plate
32
, which may be part of a heat sink (not shown) or the like, may be positioned adjacent to the land grid array-type device
20
.
As shown in
FIG. 1
, a biasing assembly
34
such as springs
36
,
38
is generally required to maintain a large, relatively constant force “F
1
” on the board, connector and device. Such a biasing assembly
34
is usually placed on the top side
14
of the printed circuit board
22
, adjacent to the second backing plate
32
, as shown in FIG.
1
. In general, with a linear spring, the force “F” provided by a spring is directly proportional to the spring constant “K” multiplied by the linear deflection “X” (F=KX). A spring having a low spring constant “K” is most desirable in this application in order to keep the spring force as consistent as possible. Specifically, manufacturing tolerances can vary among different installations. In addition, changes in environmental conditions such as temperature and creep of various components may cause the spring to deflect. Because of F=KX, a large spring constant “K” multiplied by even a small change in deflection “X” of the spring would produce a relatively large fluctuation in the force “F” provided by the spring.
Since a large force “F” is required and a low spring constant “K” is most desirable, the linear deflection “X” of any linear spring used in this application must be large. Furthermore, since a spring with more coils deflects a greater total distance than the same type of spring with fewer coils, a coil spring used in this application must be relatively long. Specifically with reference to
FIG. 1
, in order to provide a sufficient force “F” to oppose the large forces “F
0
” generated by the pads
26
on the electrical connector
24
, the length “L1” of each spring
36
,
38
(shown compressed) must be relatively large. In today's small, densely-packed computers and electronics, the distance required for such springs
36
,
38
may not be available on the top side
14
of a printed circuit board
22
. Even if such a distance is available, providing a more compact biasing assembly is more desirable.
Oftentimes, a heat sink must be installed over an electrical component such as a land grid array-type device in order to dissipate heat generated by the device. A heat sink is typically constructed from a heat conductive material such as, for example, aluminum, magnesium, or copper, and has a base portion with a plurality of cooling fins attached thereto. The base portion typically draws heat from the electrical component and then spreads and transfers the heat to the cooling fins. The base of a heat sink is typically positioned directly adjacent to the land grid array-type device, possibly with thermal interface material therebetween.
Adding a heat sink to an electronic circuit assembly presents the further problem of providing a thermal connection between a heat sink and a land grid array-type device while also providing an electrical connection between the land grid array-type device, an electrical connector, and a printed circuit board. A biasing assembly (e.g.,
34
described above) is generally required to provide a compressive force in order to maintain the necessary connections between the heat sink, land grid array-type device, electrical connector, and printed circuit board. However, during installation thereof, the force must be applied as uniformly as possible to avoid rocking and possibly damaging the land grid array-type device, electrical connector, and printed circuit board.
Thus, it is an object of the present invention to provide a backing plate assembly which includes a biasing assembly to provide a constant compressive force on a printed circuit board, electrical connector and land grid array-type device.
It is also an object of the present invention to provide a heat sink assembly which includes a biasing assembly to provide a constant compressive force on a heat sink, printed circuit board, electrical connector and land grid array-type device.
It is a further object of the present invention to provide a biasing assembly having a relatively low spring constant which provides a relatively large compressive force on a heat sink (if present), printed circuit board, electrical connector, and land grid array-type device, yet does not require a relatively large distance on the top or bottom side of the printed circuit board.
It is also an object of the present invention to provide a spring-loaded backing plate assembly as a single, compact unit positioned on the back side of a printed circuit board.
It is a further object of the present invention to use a simple, relatively low-cost leaf spring assembly, rather than a coil spring assembly, as the biasing assembly in a spring-loaded backing plate or heat sink assembly.
It is a further object of the present invention to provide a spring-loaded backing plate or heat sink assembly which provides a predetermined, constant force upon every installation thereof in a circuit assembly.
It is a further object of the present invention to provide a method for installing a spring-loaded heat sink assembly on a circuit assembly which applies biasing force in a uniform manner and prevents rocking of the components.
It is a further object of the present invention to provide a tool for inst
Cromwell S. Daniel
Peterson Eric C.
Duverne Jean F.
Hewlett--Packard Development Company, L.P.
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