Electrical connectors – Preformed panel circuit arrangement – e.g. – pcb – icm – dip,... – With provision to conduct electricity from panel circuit to...
Reexamination Certificate
2000-04-14
2001-10-09
Sircus, Brian (Department: 2839)
Electrical connectors
Preformed panel circuit arrangement, e.g., pcb, icm, dip,...
With provision to conduct electricity from panel circuit to...
C439S066000
Reexamination Certificate
active
06299460
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to electronic circuit assemblies including land grid array-type devices, and more particularly to backing plates and biasing assemblies for circuit assemblies including land grid array-type devices.
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
are 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
1
” to oppose the large forces “F
0
” generated by the pads
26
on the electrical connector
24
, the length “L
1
” 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.
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 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 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 assembly.
It is a further object of the present invention to provide a spring-loaded backing plate assembly which provides a predetermined, constant force upon every installation thereof in a circuit assembly.
SUMMARY OF THE INVENTION
In accordance with these and other objects, the present invention is directed to a spring-loaded backing plate assembly for use with a printed circuit board, an electrical connector, and a land grid array-type device. The assembly comprises a backing plate adapted to support the printed circuit board and one or more leaf springs. The backing plate may comprise a channel portion formed by a plurality of retaining walls. A retainer assembly holds the leaf springs in a preloaded state against the backing plate and transfers compressive force from the leaf springs to the printed circuit board, electrical connector, and land grid array-type device. The retainer assembly may comprise at least one post extending laterally through openings in the backing plate and the leaf springs. A pin extending laterally through an opening in the post is adapted to retain the leaf springs on the post and against the backing plate.
The present invention is also directed to a circuit assembly comprising a printed circuit board, a land grid array-type device, and an electrical connector disposed therebetween. The circuit assembly also comprises the spring-loaded backing plate assembly described above. The circuit assembly further comprises a connector assembly extending through the spring-loaded backing plate assembly, the printed circuit board, the electrical connector, and the land grid array-type device. The connector assembly may comprise the retainer assembly described above, as well as at least one fastener (which may be a captive screw) which is adapted to be connected to the retainer assembly. The circuit assembly may further comprise a second backing plate (which may be part of a heat sink or the like) which is adapted to support the land grid array-type device, and an insulator disposed between the land grid array-type device and the second backing plate.
A method for assembling a spring-loaded backing plate assembly is also disclosed. The method comprises the steps of placi
Haselby Jeffrey T.
Peterson Eric C.
Hewlett -Packard Company
Prasad Chandrika
Sircus Brian
LandOfFree
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