U.S. patent application number 10/612229 was filed with the patent office on 2004-05-13 for pre-curved spring bolster plate.
Invention is credited to Cromwell, Stephen Daniel, Hensley, James David.
Application Number | 20040089937 10/612229 |
Document ID | / |
Family ID | 25354676 |
Filed Date | 2004-05-13 |
United States Patent
Application |
20040089937 |
Kind Code |
A1 |
Hensley, James David ; et
al. |
May 13, 2004 |
Pre-curved spring bolster plate
Abstract
A method and apparatus to mount a pre-curved bolster plate to a
substrate. One embodiment of the invention involves a method to
assemble a pre-curved bolster plate on a substrate. A second
embodiment of the invention involves a method to fabricate a
pre-curved bolster plate. A third embodiment of the invention
involves an assembled substrate with a pre-curved bolster plate on
the opposite side of the assembled substrate, under an electrical
contact area of a component on the assembled substrate.
Inventors: |
Hensley, James David;
(Rocklin, CA) ; Cromwell, Stephen Daniel; (Penryn,
CA) |
Correspondence
Address: |
HEWLETT-PACKARD COMPANY
Intellectual Property Administration
P.O. Box 272400
Fort Collins
CO
80527-2400
US
|
Family ID: |
25354676 |
Appl. No.: |
10/612229 |
Filed: |
July 1, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10612229 |
Jul 1, 2003 |
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09870044 |
May 29, 2001 |
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6635513 |
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Current U.S.
Class: |
257/688 ;
438/106 |
Current CPC
Class: |
H05K 7/1007 20130101;
H05K 3/325 20130101 |
Class at
Publication: |
257/688 ;
438/106 |
International
Class: |
H01L 021/48; H01L
021/44; H01L 023/48; H01L 021/50 |
Claims
What is claimed is:
1. A method to assemble a pre-curved bolster plate to one side of a
substrate having a first side and a second side, comprising:
attaching a component to an electrical contact area on said first
side of said substrate; and attaching said pre-curved bolster plate
on said second side of said substrate, wherein said pre-curved
bolster plate is attached to said second side opposite said
electrical contact area on said first side of said substrate.
2. The method of claim 1, wherein said component is a land grid
array (LGA) component.
3. The method of claim 1, wherein said substrate is selected from a
group of substrates consisting of: a printed circuit board (PCB), a
multi-chip module (MCM), and a flexible substrate.
4. The method of claim 1, wherein said pre-curved bolster plate
includes a material selected from the group consisting of: a
stainless steel alloy, a powder-coated spring steel alloy, a plated
spring steel alloy, a painted spring steel alloy, a titanium steel
alloy, a carbon steel alloy, a magnesium alloy, and an aluminum
alloy.
5. The method of claim 1, wherein said pre-curved bolster plate has
a spherical curvature.
6. The method of claim 1, wherein said pre-curved bolster plate has
a cylindrical curvature.
7. The method of claim 1, wherein said pre-curved bolster plate has
a radius of curvature in excess of 100 inches (254
centimeters).
8. A method to fabricate a pre-curved bolster plate, comprising:
selecting a set of physical dimensions of said pre-curved bolster
plate; estimating an initial radius of curvature for said
pre-curved bolster plate; modeling said pre-curved bolster plate
after assembly on a substrate; estimating a more precise radius of
curvature for said pre-curved bolster plate after modeling said
pre-curved bolster plate after assembly on said substrate; cutting
said pre-curved bolster plate according to said set of physical
dimensions; and stamping said pre-curved bolster plate to achieve
said more precise radius of curvature.
9. The method of claim 9, wherein said pre-curved bolster plate is
fabricated from a material selected from the group of materials
consisting of: a stainless steel alloy, a powder-coated spring
steel alloy, a plated spring steel alloy, a painted spring steel
alloy, a titanium steel alloy, a carbon steel alloy, a magnesium
alloy, and an aluminum alloy.
10. The method of claim 9, wherein said pre-curved bolster plate is
stamped to achieve a spherical curvature.
11. The method of claim 9, wherein said radius of curvature is
greater than 100 inches (254 centimeters).
12. The method of claim 9, wherein said pre-curved bolster plate is
stamped to achieve a cylindrical curvature.
13. An assembled substrate, comprising a substrate having a first
and a second side, and an electrical contact area on said first
side; an electrical component having a plurality of leads attached
to said electrical contact area of said substrate; and a pre-curved
bolster plate attached to said second side of said substrate
opposite said electrical contact area of said substrate.
14. The assembled substrate of claim 13, wherein said substrate is
selected from the group of substrates consisting of: a printed
circuit board (PCB), a multi-chip module (MCM), and a flexible
substrate.
15. The assembled substrate of claim 13, wherein said component is
a land grid array (LGA) component.
16. The assembled substrate of claim 13, wherein said pre-curved
bolster plate is fabricated from a material selected from the group
of materials consisting of: a stainless steel alloy, a
powder-coated spring steel alloy, a plated spring steel alloy, a
painted spring steel alloy, a titanium steel alloy, a magnesium
alloy, and an aluminum alloy.
17. The assembled substrate of claim 13, wherein said pre-curved
bolster plate has a spherical curvature.
18. The assembled substrate of claim 13, wherein said pre-curved
bolster plate has a cylindrical curvature.
19. The assembled substrate of claim 13, wherein said pre-curved
bolster plate has a radius of curvature in excess of 100 inches
(254 centimeters).
20. The assembled substrate of claim 13, wherein said pre curved
bolster plate has a radius of curvature less than 100 inches (254
centimeters).
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates generally to a bolster plate to
support a substrate subject to high clamping forces for IC
components, and more specifically relates to a bolster plate to
support a printed circuit board assembled with one or more land
grid array (LGA) IC components.
[0003] 2. Description of the Prior Art
[0004] In many data processing systems (e.g., computer systems,
programmable electronic systems, telecommunication switching
systems, control systems, and so forth) very large pin count
electrical components (e.g., application specific integrated
circuits and processor chips) are assembled on substrates (e.g.,
printed circuit boards, other flexible substrates, multi-chip
modules, and equivalents). One type of packaging that is frequently
used for a very large pin count electrical component is what is
commonly known as a land grid array (LGA) component. Electrical
connections between the LGA component pins and the corresponding
conductive pads on the substrate are frequently achieved by
compressing an elastomeric insulating material containing several
perpendicular conductive channels (e.g., buttons or columns filled
with conductive balls or conductive threads).
[0005] In order to achieve reliable electrical connection between
the pins and the pads, such LGA components are clamped by bolts to
the substrate with high perpendicular clamping forces (exceeding
several hundred pounds or several hundred newtons of force).
However, such large perpendicular forces can cause distortion in
the normally flat substrate, and the lack of flatness can cause
poor electrical contacts that produce a permanent or an
intermittent failure in system operation. Therefore, a bolster
plate is frequently attached under a LGA component clamped area of
the substrate to support the substrate. The bolster plate provides
extra rigidity to the substrate, and the bolster plate helps to
maintain the flatness of the substrate under the LGA component.
[0006] FIG. 1 illustrates a conventional bolster plate 102
assembled under a substrate (e.g., a printed circuit board) 104,
opposite to the attachment of a LGA component 106 by clamp 108 into
a socket 110 on the top of the substrate 104. The conventional
bolster plate 102 is designed to provide flatness and rigidity to
the substrate 104, and provide a uniform load distribution across
the contact region of the LGA component 106 when the clamp 108 is
bolted to the substrate 104 by bolts 114 and springs 112.
[0007] Conventional bolster plates are typically fabricated from a
thick, heavy metal plate coated with one or more insulating layers,
or they are fabricated from an expensive thermo-set composite
material (e.g., a graphite fiber epoxy composite). Frequently, such
bolster plates are constrained in thickness and dimensions by the
increasing packing densities of nearby substrates. Thick and heavy
bolster plates may touch and damage adjacent components on adjacent
substrates, and can be especially detrimental to system reliability
when the system is subject to shock and vibration. However, thin
and light bolster plates may distort and fail to adequately support
the substrate when high clamping forces are used for high pin count
LGA components. Since the pin counts for IC components are
continually increasing, clamping forces for LGA components and the
resulting substrate distortions will increase. Without an improved
bolster plate to counter such distortions, there will be an
increasing number of poor electrical contacts between LGA
components and the substrates, resulting in increasing operational
and reliability failures.
[0008] It would be desirable to provide an improved bolster plate
that can supply the necessary mechanical support to a substrate,
and maintain the desired flatness of the electrical contact area
under an IC component. In addition, this improved bolster plate
would preferably be formed from thinner material, due to the
reduction in open space adjacent to the substrate in a computer
system.
SUMMARY OF THE INVENTION
[0009] The present invention provides an improved bolster plate
that can supply the necessary mechanical support to a substrate,
and maintain the desired flatness of the electrical contact area
under an IC component. In addition, this improved bolster plate can
be formed from thinner material, compared to the material needed in
a conventional bolster plate.
[0010] A first aspect of the invention is directed to a method to
assemble a pre-curved bolster plate to one side of a substrate
having a first side and a second side. The method includes
attaching a component to an electrical contact area on the first
side of the substrate; and attaching the pre-curved bolster plate
to the second side of the substrate, wherein the precurved bolster
plate is attached to the second side opposite the electrical
contact area on the first side of the substrate.
[0011] A second aspect of the invention is directed to a method to
fabricate a pre-curved bolster plate. The method includes selecting
a set of physical dimensions of the pre-curved bolster plate;
estimating an initial radius of curvature for the pre-curved
bolster plate; modeling the pre-curved bolster plate after assembly
on a substrate; estimating a more precise radius of curvature for
the pre-curved bolster plate after modeling the pre-curved bolster
plate after assembly on the substrate; cutting the pre-curved
bolster plate according to the set of physical dimensions; and
stamping the pre-curved bolster plate to achieve the more precise
radius of curvature.
[0012] A third aspect of the invention is directed to an assembled
substrate. The assembled substrate includes a substrate having a
first and a second side, and an electrical contact area on the
first side; an electrical component having a plurality of leads
attached to the electrical contact area of the substrate; and a pre
curved bolster plate attached to the second side of said substrate
opposite the electrical contact area of the substrate.
[0013] These and other objects and advantages of the invention will
become apparent to those skilled in the art from the following
detailed description of the invention and the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 illustrates a conventional bolster plate prior to
assembly under a substrate (e.g., a printed circuit board),
opposite to the attachment of a LGA component to the top of the
substrate.
[0015] FIG. 2 illustrates a pre-curved bolster plate prior to
assembly under a substrate, opposite to the attachment of a LGA
component to the top of the substrate.
[0016] FIG. 3A illustrates one embodiment of a pre-curved bolster
plate with a spherical curvature.
[0017] FIG. 3B illustrates one embodiment of a precurved bolster
plate with a cylindrical curvature.
[0018] FIG. 4 illustrates a side view of a precurved bolster plate
with a spherical or cylindrical curvature that is deflected into a
flat plate parallel to the plane of the substrate during the
application of the perpendicular clamping force to the substrate
and pre-curved bolster plate.
[0019] FIG. 5 shows one flow chart for a method to assemble a
pre-curved bolster plate on a substrate as shown in FIG. 2 in
accordance with one embodiment of the present invention.
[0020] FIG. 6 shows a flow chart for a method to fabricate a
pre-curved bolster plate in accordance with one preferred
embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0021] The present invention provides an improved bolster plate
that is relatively thinner and lighter in weight than conventional
bolster plates. This improved bolster plate is attached to a
substrate under an electrical component mounted on the substrate,
such as a printed circuit board (PCB) or multi-chip module. While
the discussion below is directed to an application of the invention
to an LGA assembled on a substrate (e.g., a PCB), the invention can
also be applied to other types of electrical components assembled
on a flexible substrate (e.g., multi-chip modules, and other
substrates upon which electrical components can be assembled).
[0022] FIG. 2 illustrates one embodiment of a pre-curved bolster
plate 202 prior to assembly under a substrate (e.g., a PCB) 104,
opposite to the attachment of a LGA component 106 to the top of the
substrate 104. The LGA component 106 is inserted in a socket 110,
and the LGA component 106 is clamped to the substrate 104 by clamp
108. The clamping of the LGA component 106 is complete when the
clamp 108 is bolted to the substrate 104 by bolts 114 and springs
112. The pre-curved bolster plate 202 is designed to provide
flatness and rigidity to the substrate 104, and provide a uniform
load distribution across the contact region of the LGA component
106.
[0023] The pre-curved bolster plate 202 can be fabricated from the
following materials: a stainless steel alloy, a titanium steel
alloy, a carbon steel alloy, a magnesium alloy, and an aluminum
alloy. One preferred embodiment of the invention has a pre-curved
bolster plate fabricated from a stainless steel alloy. Stainless
steel is corrosion resistant and would not require plating or
painting after stamping. Stainless steel also has sufficient
strength and stiffness to allow for net-shape stamping and not
require post-stamping heat treatment. This avoids the inherent
warpage and distortion associated with heat-treating. The
pre-curved bolster plate 202 can be designed to have a spherical,
cylindrical, compound multi-spherical, or compound
multi-cylindrical curvature (similar to cathedral ceilings) that
will counteract the perpendicular clamping force to provide
flatness and rigidity to the PCB 104, and provide a uniform load
distribution across the contact region of the LGA component
106.
[0024] FIG. 3A illustrates one embodiment of a pre-curved bolster
plate 202 with a spherical curvature. The radius of curvature
(e.g., a radius of curvature typically greater than or less than
approximately 100 inches or 254 centimeters) can be determined by
calculating the curvature in a flat plate of the bolster plate
material that would result from the perpendicular clamping force.
The spherical curvature can be achieved by stamping an originally
flat plate of material. An alternative preferred embodiment of the
invention uses a mold to fabricate a bolster plate with a spherical
curvature.
[0025] FIG. 3B illustrates one embodiment of a pre curved bolster
plate 202 with a cylindrical curvature. A bolster plate with a
cylindrical curvature may be easier to calculate and stamp, and
provide many of the benefits of a bolster plate with a spherical
curvature. The cylindrical curvature can be achieved by stamping an
originally flat plate of material. An alternative preferred
embodiment of the invention uses a mold to fabricate a bolster
plate with a cylindrical curvature.
[0026] FIG. 4 illustrates a side view of a pre-curved bolster plate
202 with a spherical, cylindrical, or compound curvature that is
deflected into a flat plate parallel to the plane of the substrate
104 during the application of the perpendicular clamping force to
the substrate (e.g., a PCB) 104 and pre-curved bolster plate 202.
The LGA component 106 is in a socket 110, and the LGA component 106
is clamped to the substrate 104 by clamp 108. The clamping force on
the LGA component 106 is applied when the clamp 108 is bolted to
the substrate 104 by bolts 114 and springs 112. The pre-curved
bolster plate 202 is designed to provide a uniform load
distribution across the contact region of the LGA component
106.
[0027] FIG. 5 shows one flow chart for a method to assemble a
pre-curved bolster plate on a substrate as shown in FIG. 2 in
accordance with one embodiment of the present invention. The method
starts in operation 502, and is followed by operation 504. In
operation 504, a component (e.g., a LGA component) is attached to
an electrical contact area on one side of the substrate. Operation
506 is next, where the pre-curved bolster plate is attached on the
other side of the substrate, wherein the pre curved bolster plate
is attached opposite to the component and the electrical contact
area on the other side of the substrate. Operation 508 is the end
of the method.
[0028] FIG. 6 shows a flow chart for a method to fabricate a
pre-curved bolster plate in accordance with one preferred
embodiment of the present invention. The method starts in operation
602, and is followed by operation 604. In operation 604, a hand
calculation is made of the radius of curvature of a flat bolster
plate under a uniform load predicted from the clamping force that
will be applied to the LGA assembled on a substrate. In operation
606, a 3-D computer aided design (CAD) software package (e.g.,
Pro/ENGINEER, available from PTC Corporation with corporate
headquarters in Needham, Mass.; SolidDesigner, available from
CoCreate Software, Inc. with corporate headquarters in Fort
Collins, Colo.; SolidWorks, available from SolidWorks Corporation
with corporate headquarters in Concord, Mass.; or an equivalent CAD
package) is used to create a model of the pre-curved bolster plate
assuming the previously estimated radius of curvature. Then
operation 608 is next. In operation 608, a finite element analysis
(FEA) software package (e.g., Pro/MECHANICA, available from PTC
Corporation with corporate headquarters in Needham, Mass.; Ansys,
available from Ansys, Inc. with corporate headquarters in
Canonsburg, Pa.; Cosmos, available from Structural Research &
Analysis Corporation with corporate headquarters in Los Angeles,
Calif.; or an equivalent FEA package) is used to model the stresses
and the predict the final shape of the pre-curved bolster plate
after assembly of the pre-curved bolster plate and the component to
the substrate. In operation 610, a test is made to determine if the
FEA software package predicts that that the pre curved bolster
plate deflects to a flat plate after assembly. If the test of
operation 610 determines that the pre-curved bolster plate will not
deflect to a flat plate, operation 612 is next where the operator
decides on a new radius of curvature. Then operations 606, 608, and
610 are repeated. If the test of the operation 610 determines that
the pre-curved bolster plate will deflect to a flat plate, then
operation 614 is next. In operation 614 a physical pre-curved
bolster plate prototype is fabricated. Operation 616 is next, where
the precurved bolster plate is assembled to the substrate to verify
that the pre-curved bolster plate will become a flat plate. Then
operation 618 is next, where a test is made to determine if the
pre-curved bolster plate becomes flat. If the test of operation 618
verifies that pre-curved plate does not become flat, then operation
612 is next. If the test of operation 618 verifies that the
precurved bolster plate becomes flat, then the method ends in
operation 620.
[0029] The embodiments of the invention discussed above mainly
described examples of substrates assembled with LGA components.
However, alternative embodiments of the invention can be applied to
other components (e.g., clamped IC components, transformers, power
supplies, connectors, or other devices that can cause substrate
distortion by an attachment force, clamping force, or from the
weight of the component).
[0030] The exemplary embodiments described herein are for purposes
of illustration and are not intended to be limiting. Therefore,
those skilled in the art will recognize that other embodiments
could be practiced without departing from the scope and spirit of
the claims set forth below.
* * * * *