U.S. patent application number 12/559165 was filed with the patent office on 2010-01-07 for memory module assembly including heat sink attached to integrated circuits by adhesive and clips.
This patent application is currently assigned to Super Talent Electronics, Inc.. Invention is credited to Abraham C. Ma, Jim Ni.
Application Number | 20100000655 12/559165 |
Document ID | / |
Family ID | 41211110 |
Filed Date | 2010-01-07 |
United States Patent
Application |
20100000655 |
Kind Code |
A1 |
Ni; Jim ; et al. |
January 7, 2010 |
Memory Module Assembly Including Heat Sink Attached To Integrated
Circuits By Adhesive And Clips
Abstract
A memory module assembly includes two-plate heat sink attached
to one or more of the integrated circuits (e.g., memory devices) of
a memory module PCBA by adhesive. The adhesive is either
heat-activated or heat-cured. The adhesive is applied to either the
memory devices or the heat-sink plates, and then compressed between
the heat-sink plates and memory module using a fixture. The fixture
is then passed through an oven to activate/cure the adhesive. The
two heat sink plates are then secured by a clip to form a rigid
frame.
Inventors: |
Ni; Jim; (San Jose, CA)
; Ma; Abraham C.; (Fremont, CA) |
Correspondence
Address: |
BEVER HOFFMAN & HARMS, LLP;901 Campisi Way
Suite 370
Campbell
CA
95008
US
|
Assignee: |
Super Talent Electronics,
Inc.
San Jose
CA
|
Family ID: |
41211110 |
Appl. No.: |
12/559165 |
Filed: |
September 14, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11691452 |
Mar 26, 2007 |
7609523 |
|
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12559165 |
|
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|
10956893 |
Sep 29, 2004 |
7215551 |
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11691452 |
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Current U.S.
Class: |
156/60 |
Current CPC
Class: |
H01L 23/467 20130101;
Y10T 156/10 20150115; H01L 23/3672 20130101; H01L 2924/0002
20130101; H01L 25/105 20130101; H01L 23/4093 20130101; H01L 23/42
20130101; H01L 2924/00 20130101; H01L 2924/0002 20130101 |
Class at
Publication: |
156/60 |
International
Class: |
B32B 37/02 20060101
B32B037/02 |
Claims
1. A method for manufacturing a memory module assembly comprising:
forming a memory module printed circuit board assembly (PCBA)
including: a substrate having opposing first and second surfaces, a
plurality of wiring traces formed on the first and second surfaces,
at least some of the wiring traces being connected to metal contact
pads formed along a connector edge of the substrate, and a
plurality of first integrated circuit (IC) devices mounted on the
first surface of the substrate such that an upper surface of each
of the plurality of first IC devices faces away from the first
surface of the substrate; applying an adhesive to one of a planar
first underside surface of a first heat-sink plate and the upper
surface of at least one of said plurality of first IC devices;
mounting the first heat-sink plate and memory module PCBA into a
fixture such that the planar first underside surface of the first
heat-sink plate is pressed against the at least one of said
plurality of first IC devices with the adhesive pressed
therebetween, and a first outer surface of the first heat-sink
plate that is opposed to the first underside surface contacts a
first portion of the fixture; heating the fixture at a first
temperature for a period of time such that the adhesive undergoes
at least one of activation and curing; and cooling the fixture to a
second temperature that is lower than the first temperature.
2. The method according to claim 1, wherein mounting the first
heat-sink plate and the memory module PCBA in the fixture further
comprises: aligning and mounting the first heat-sink plate onto the
memory module PCBA; and placing the first heat-sink plate and the
memory module PCBA into a recess formed in the fixture, and
manipulating a spring clamp such that the first heat-sink is
pressed against the associated IC device.
3. The method according to claim 1, wherein applying the adhesive
further comprises applying to the planar underside surface of the
first heat-sink plate at least one of a thermal-bond adhesive film
and a thermal conductive film.
4. The method according to claim 1, wherein applying the adhesive
further comprises applying to the upper surface of said at least
one of the plurality of first IC devices one of a thermal-bond
adhesive film and a thermal conductive film.
5. The method according to claim 1, wherein heating the fixture
comprises placing the fixture in an oven maintained at a
temperature of at least 80.degree. C. for approximately 15
minutes.
6. The method according to claim 1, wherein forming the memory
module PCBA further comprises mounting a plurality of second IC
devices on the second surface of the substrate such that an upper
surface of each of the plurality of second IC devices faces away
from the substrate; wherein applying adhesive further comprises
applying said adhesive to one of a planar second underside surface
of a second heat-sink plate and the upper surface of at least one
of said plurality of second IC devices; wherein said mounting
further comprises mounting said second heat-sink plate into said
fixture such that the planar second underside surface of the second
heat-sink plate is pressed against at least one of said plurality
of second IC devices with the adhesive pressed therebetween, and a
second outer surface of the second heat-sink plate that is opposed
to second underside surface contacts a second portion of the
fixture.
7. The method according to claim 6, wherein forming the memory
module PCBA further comprises: mounting a first plurality of said
first integrated circuit (IC) devices and a second plurality of
said first IC devices on the first surface of the substrate such
that upper surfaces of the first and second pluralities of first IC
devices define a first plane that is parallel to the first surface
of the substrate, mounting a third IC device on the first surface
between the first and second pluralities of first devices, the
third IC device having an upper surface defining a second plane
that is parallel to the first surface of the substrate, wherein the
first plane is located between the second plane and the first
surface of the substrate; wherein the first heat-sink plate
includes a first recessed region defined by a first upper surface
region and an opposing first planar underside surface region, a
second recessed region having a second upper surface region and an
opposing second planar underside surface region, and a raised
pocket structure defining a third upper surface region and an
opposing third planar underside surface region, and the pocket
region is disposed between the first and second recessed regions,
and wherein said mounting comprises mounting said first heat-sink
plate such that a first recessed region is secured to at least one
of said first plurality of said first IC devices, a second recessed
region is secured to at least one of said second plurality of said
first IC devices, and a raised pocket structure disposed between
the first and second recessed regions is disposed over the third IC
device.
8. The method according to claim 7, wherein mounting the plurality
of first IC devices comprises mounting dynamic random access memory
(DRAM) devices, wherein mounting the third IC device comprises
mounting an advanced memory buffer (AMB) device that is connected
to each of the first and second pluralities of first IC devices by
way of a bus disposed on said substrate.
9. The method according to claim 6, wherein at least one side edge
of the substrate defines a positioning notch, and wherein said
mounting further comprises positioning said first and second
heat-sink plates such that side wall structures disposed on each of
said first and second heat-sink plates abutting a corresponding one
of said first and second surfaces adjacent to said at least one
side edge, and such that a tab disposed on at least one of the
first and second heat-sink plates extends from a corresponding one
of said side wall structures into the positioning notch.
10. The method according to claim 9, wherein the first heat-sink
plate comprises said tab, and wherein said mounting further
comprises positioning said second heat sink plate such that a
groove formed on said second heat sink plate receives an end of the
tab.
11. The method according to claim 9, wherein said mounting further
comprises positioning said first and second heat-sink plates such
that first and second tab portions respectively disposed on the
first and second heat-sink plates extend partially into the
notch.
12. The method according to claim 6, wherein said mounting
comprises connecting at least one clip to said first and second
heat-sink plates such that a first engaging portion of said at
least one clip is connected to the first outer surface of the first
heat-sink plate, wherein said at least one clip includes a second
engaging portion of said at least one clip is connected to the
second outer surface of the second heat-sink plate, wherein said at
least one clip includes a linking member connected between the
first and second engaging members.
13. The method according to claim 12, wherein connecting said at
least one clip to said first and second heat-sink plates comprises
connecting a first portion of said at least one clip to at least
one first hook protruding from said first outer surface of said
first heat-sink plate, and connecting a second portion of said at
least one clip to at least one second hook protruding from said
second outer surface of said second heat-sink plate.
14. The method according to claim 12, wherein connecting said at
least one clip to said first and second heat-sink plates comprises
inserting a first protruding end structure of said at least one
clip into at least one first slot defined on said first outer
surface of said first heat-sink plate, and inserting a second
protruding end structure of said at least one clip into at least
one second slot defined on said second outer surface of said second
heat-sink plate.
15. The method according to claim 12, wherein connecting said at
least one clip to said first and second heat-sink plates comprises:
connecting a first single-piece clip between the first upper
surface region and the second outer surface; and connecting a
second single-piece clip between the second upper surface region
and the second outer surface.
16. The method according to claim 6, wherein applying the adhesive
further comprises applying a heat-activated adhesive material
exhibiting a first, relatively low adherence when heated to a
first, relatively high temperature, and exhibiting a second,
relatively high adherence when subsequently cooled to a second,
relatively low temperature.
17. The method according to claim 6, wherein applying the adhesive
further comprises applying one of a high thermal conductive
adhesive film and a thermal-bond adhesive film.
18. The method according to claim 7, wherein applying the adhesive
comprises applying to said plurality of first IC devices one of a
high thermal conductive adhesive film and a thermal-bond adhesive
film, and disposing a thermal paste between said third IC device
and said raised pocket structure.
19. A method for manufacturing a memory module assembly comprising:
forming a memory module printed circuit board assembly (PCBA)
including: a substrate having opposing first and second surfaces, a
plurality of first wiring traces formed on at least one of the
first and second surfaces, each of the first wiring traces being
connected to an associated metal contact pad formed along a
connector edge of the substrate, the substrate also having opposing
first and second side edges disposed at opposing ends of the
connector edge, wherein each of said first and second side edges
defines a notch; and a first plurality of first integrated circuit
(IC) devices and a second plurality of said first IC devices
disposed on the first surface of the substrate such that upper
surfaces of the first and second pluralities of first IC devices
define a first plane that is parallel to the first surface of the
substrate, and a second IC device disposed on the first surface
between the first and second pluralities of first devices, the
second IC device having an upper surface defining a second plane
that is parallel to the first surface of the substrate, wherein the
first plane is located between the second plane and the first
surface of the substrate; applying an adhesive to one of first and
second planar underside surfaces of a first heat sink plate and the
upper surface of at least one of said first and second pluralities
of said first IC devices, wherein the first heat-sink plate
includes a first recessed region having a first planar upper
surface and said first planar underside surface, disposed opposite
to the first planar upper surface, a second recessed region having
a second planar upper surface and said second planar underside
surface disposed opposite to the second planar upper surface, and a
raised pocket region defining a third planar upper surface and an
opposing third planar underside surface, the pocket region being
disposed between the first and second recessed regions, mounting
the first heat-sink plate and memory module PCBA into a fixture
such that the planar first underside surface is pressed against the
first plurality of first IC devices with the adhesive pressed
therebetween, the planar second underside surface is pressed
against the second plurality of first IC devices with the adhesive
pressed therebetween, and the pocket region is disposed over the
second IC device, and such that the first planar upper surface and
the second planar upper surface contact a first portion of the
fixture; and heating the fixture at a first temperature for a
period of time such that the adhesive undergoes at least one of
activation and curing.
20. The method according to claim 19, wherein at least one side
edge of the substrate defines a positioning notch, and wherein said
mounting further comprises positioning said first heat-sink plate
such that a side wall structure disposed on said first heat-sink
plate abuts said first surfaces adjacent to said at least one side
edge, and such that a tab disposed on the first heat-sink plate
extends from said side wall structure into the positioning
notch.
21. The method according to claim 19, wherein applying the adhesive
comprises applying to said plurality of first IC devices one of a
high thermal conductive adhesive film and a thermal-bond adhesive
film, and disposing a thermal paste between said second IC device
and said raised pocket structure.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional of U.S. application
Ser. No. 11/691,452, filed Mar. 26, 2007 which is a
continuation-in-part of co-owned U.S. application Ser. No.
10/956,893, filed Sep. 29, 2004, entitled "MEMORY MODULE ASSEMBLY
INCLUDING HEAT SINK ATTACHED TO INTEGRATED CIRCUITS BY ADHESIVE",
now U.S. Pat. No. 7,215,551, which is incorporated herein by
reference in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates to standardized memory modules for
expanding the memory capacity of personal computers and other
computing systems, and more particularly to memory module
assemblies that include heat-sink structures.
BACKGROUND OF THE INVENTION
[0003] Heat sinks have been widely used to assist in cooling
electronic components. Some microprocessors have heat sinks
attached to allow for higher-frequency operation. Other components
such as memory modules may also benefit from heat sinks.
[0004] Most personal computers (PC's) are shipped with sockets for
memory modules so that their owners can later add additional
modules, increasing the memory capacity of the PC. Other non-PC
devices may also use memory modules designed for PC's. High-volume
production and competition have driven module costs down
dramatically, benefiting the buyer.
[0005] Memory modules are made in many different sizes and
capacities, with the older 30-pin modules replaced by 72-pin,
168-pin, and other size modules. The "pins" were originally pins
extending from the module's edge, but now most modules are
lead-free, having metal contact pads, fingers, or leads. The
modules are small in size, some being about 5.25 inches long and
1.2 or 1.7-inches high.
[0006] Conventional memory modules include a small printed-circuit
board (PCB) substrate and several surface mounted components (e.g.,
memory devices) mounted on one or both surfaces of the PCB
substrate. The PCB substrate is typically a multi-layer board with
alternating laminated layers of fiberglass insulation and foil or
metal interconnection layers. The contact pads (or other contact
structures) are typically aligned along a bottom (connector) edge
of the PCB substrate. The interconnect layers define wiring traces
that provide signal paths between the surface mounted components
and the contact pads. The surface mounted components (e.g., memory
devices) are soldered or otherwise attached to one or both surfaces
of the substrate, with each component typically including one or
more integrated circuit (IC) "chips" that are packaged in
inexpensive surface-mount packages such as small-outline J-leaded
(SOJ) packages, plastic leaded chip carriers (PLCC's), thin
small-outline packages (TSOP) or small-outline (SO) packages. The
number of memory devices mounted on the PCB substrate of a memory
module depends on the capacity and the data-width of the memory
chips and the size of the memory module.
[0007] FIG. 15 is a diagram showing a memory module with
dynamic-random-access memory (DRAM) devices. The memory module
contains substrate 10, with surface-mounted DRAM devices 20 mounted
directly to the front surface or side of substrate 10, while more
DRAM devices (not visible) are usually mounted to the back side or
surface of substrate 10. Metal contact pads 12 are positioned along
the bottom or connector edge of the module on both front and back
surfaces. When the memory module is mounted into a host system
(e.g., a personal computer (PC)), metal contact pads 12 mate with
pads on a module socket (not shown) to electrically connect the
module to the host system's motherboard. Holes and/or notches 14,
16 are sometimes used to ensure that the module is correctly
positioned in the socket. For example, notch 14 can be offset from
the center of substrate 10 to ensure that the memory module cannot
be inserted backwards in a socket. Notches 16 match with clamps of
the module socket to ensure that the memory module is securely
positioned in the socket.
[0008] As processor speeds have increased, the need for faster
memory has become more critical. Various bandwidth-enhancing
methods and memory interfaces have been used. Memory chips have
higher densities and operate at higher frequencies than before,
producing more waste heat from the memory chips. Thus, a need has
arisen to remove this waste heat from memory modules.
[0009] Conventional memory module assemblies typically include
three components: the memory module PCBA and two metal heat-sink
plates that are coupled together using one or more fasteners, such
as a metal clamp. The contact between PCBA and metal heat-sink
plate is usually aided by sandwiching a tape of thermal interface
material (TIM) in-between. Various heat-sink plates have been
designed for producing such memory module assemblies. See for
example U.S. Pat. Nos. 6,362,966, 6,424,532, and 6,449,156, among
others. Clamp-on heat-sink plates for memory modules are also
known. For example, OCZ Technology produces a copper heat sink with
wider metal bands that clip the heat sink to over the front and
back surfaces of the memory module. These clip-on and clamp-on
designs increase the manufacturing costs and complexity of the
associated memory modules because they are difficult to incorporate
into automated production lines. Further, the use of clamps or
similar structures facilitates easy disassembly by users, resulting
in undesirable situations. Moreover, the presence of the clamps and
thermal interface material increase the overall thickness of the
memory module assembly, thereby taking up valuable motherboard
space.
[0010] Some memory-module heat sinks feature a closed-top design
that prevents airflow in the small gaps between the heat sink and
the memory module substrate. Often the entire top edge of the heat
sink is closed, providing no path for air to flow under the heat
sink other than back out the bottom edge, which is usually open.
Sides may be open or partially open, but the sides are much smaller
than the top and bottom edges of the memory module, limiting the
possible air-flow.
[0011] What is needed is a memory module assembly having a
protective metal heat-sink plate (shield) mounted over the surface
mounted IC devices of a memory module PCBA that both serves to
protect the PCBA and to dissipate heat generated by the IC devices,
and is easily and inexpensively produced using automated
methods.
SUMMARY OF THE INVENTION
[0012] The present invention is directed to a memory module
assembly including heat sink plates that are directly attached to
one or more of the integrated circuits (IC) devices of a memory
module printed circuit board assembly (PCBA) using an adhesive,
whereby the heat-sink plates both protect the memory module PCBA
and dissipate heat generated by the IC devices thereof. By directly
attaching the heat-sink plates to the IC devices of the memory
module PCBA, the present invention facilitates a simplified
automated manufacturing method that greatly reduces overall
production costs.
[0013] The memory module assembly of the present invention utilizes
a memory module PCBA that is essentially identical to conventional
memory modules, thus allowing the present invention to be utilized
with existing electronics. That is, similar to conventional memory
modules, the IC devices are surface mounted on both surfaces of a
printed-circuit board (PCB) substrate. The PCB substrate includes
metal contact pads arranged along a connector (bottom) edge, and
multiple wiring traces that provide signal paths between the IC
devices and the contact pads. An important aspect of the present
invention is the IC devices are packaged and surface mounted on the
PCB substrate such that an upper surface of each of these IC
devices defines a plane that is substantially parallel to the
planar PCB surface on which it is mounted, although the height of
each IC device may vary. In particular, the planar upper surfaces
of these IC devices are used to secure the memory module PCBA to
planar underside surfaces of the heat sink plates by way of the
adhesive.
[0014] According to an embodiment of the present invention, the
adhesive is a heat-activated or heat-cured adhesive that is applied
to either the upper surface of the one or more IC devices, or to
the planar underside surfaces of the heat-sink plates. When
applied, the adhesive is viscous and has a relatively low adhesion
to facilitate manipulation of the cover and memory module PCBA
until a desired orientation is achieved. The adhesive is then
compressed between the heat-sink plate and IC devices, and is held
in the compressed state using a fixture. The fixture is then passed
through an oven maintained at a specified temperature (i.e., at or
lower than the maximum safe operating temperature for the memory
module components) to activate or cure the adhesive. In one
embodiment, a heat-activated adhesive is used that exhibits a
relatively low adherence prior to being heated to a high
temperature (i.e., equal to or less than the maximum safe operating
temperature of the memory module assembly), and the heat-activated
adhesive exhibits a high adherence when subsequently cooled. In
this case, subsequent removal of the heat-sink plates from the
memory module PCBA requires reheating at a predetermined
temperature to reflow the adhesive. In another embodiment, the
heating process is used to "cure" a relatively highly thermally
conductive adhesive, subsequent separation of the heat-sink plate
requires the use of a chemical solvent to dissolve the heat-cured
adhesive. In both cases, unauthorized tampering (i.e., removal of
the heat-sink plates to access the IC devices) is rendered more
difficult and easier to detect than conventional memory modules
that utilize clips or fasteners. Further, the heat-cured adhesive
is thin and thermally conductive to reduce thermal resistance
between the IC devices and the heat-sink plates, thus facilitating
a relatively high rate of heat flow from the IC devices to maintain
relatively low operating temperatures. Thus, the use of
heat-activated and/or heat-cured adhesive facilitates a greatly
thinner memory module with heat sink and simplified assembly
process whereby the heat-sink plates are secured to protect the
memory module PCBA in a manner that reduces overall manufacturing
costs, and prevents unauthorized tampering. In other embodiments,
the adhesive maybe be a high thermal conductive adhesive film, a
thermal-bond adhesive film, a thermal paste, or a combination or
laminated structure thereof.
[0015] According to another aspect of the present invention, two
heat-sink plates are attached to the memory module PCBA such that
tabs formed on at least one of the two heat-sink plates extends
into an alignment notch formed on a side edge of the PCBA, thereby
facilitating reliable automatic alignment of the heat-sink plates
to the PCBA during the assembly and heat-treating process. In one
embodiment, a single tab extends from one heat-sink plate along the
entire alignment notch, and is engaged into a receiving structure
formed on the second heat-sink plate. In another embodiment, short
tabs extend from both heat-sink plates into the alignment notch
formed in the PCBA.
[0016] According to yet another aspect of the present invention,
two heat-sink plates are further attached to the memory module PCBA
by one or more single-piece clips to provide a more sturdy and
reliable engagement arrangement. Each single-piece clip includes a
first engaging portion connected to the first outer surface of a
first heat-sink plate, a second engaging portion connected to the
second outer surface of the opposing second heat-sink plate, and a
linking member connected between the first and second engaging
members that extends along a side edge of the PCBA. In one
embodiment, two clips are respectively mounted on opposite sides of
a centrally located Advanced Module Buffer (AMB) chip, and in other
embodiments a single clip is mounted such that engagement portions
of the clip are engaged to the heat-sink plate on opposite sides of
the AMB chip. In one embodiment, outer surfaces of the heat-sink
plates are fabricated to include holes and/or hooks that securely
engage the engaging portions of the clips, and in another
embodiment the engagement portions of the clips are inserted into
slots formed in a raised central pocket formed in the heat-sink
plate for housing the AMB chip.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIGS. 1(A) and 1(B) are an exploded perspective view and an
assembled perspective view, respectively, showing a memory module
assembly according to an embodiment of the present invention.
[0018] FIG. 2 is a top view showing a memory module PCBA of the
memory module assembly shown in FIG. 1(A).
[0019] FIG. 3 is a top view showing a heat-sink plate of the memory
module assembly shown in FIG. 1(A).
[0020] FIGS. 4(A) and 4(B) are top and cross-sectional side views
showing the memory module assembly shown in FIG. 1(A).
[0021] FIG. 5 is a cross-sectional end view showing the memory
module assembly shown in FIG. 1(A).
[0022] FIGS. 6(A), 6(B), 6(C) and 6(D) are exploded perspective,
front assembled perspective, rear assembled perspective, and
cross-sectional side views showing a FB-DIMM type memory module
assembly according to another embodiment of the present
invention.
[0023] FIGS. 7(A), 7(B) and 7(C) are exploded perspective, front
assembled perspective, rear assembled perspective views showing a
FB-DIMM type memory module assembly according to another embodiment
of the present invention.
[0024] FIGS. 8(A), 8(B) and 8(C) are exploded perspective, front
assembled perspective, and rear assembled perspective views showing
a FB-DIMM type memory module assembly according to another
embodiment of the present invention.
[0025] FIG. 9 is a simplified perspective view showing adhesive
layers associated with FB-DIMM type memory module assembly
according to another embodiment of the present invention.
[0026] FIG. 10 is a simplified perspective view showing adhesive
layers associated with FB-DIMM type memory module assembly
according to another embodiment of the present invention.
[0027] FIGS. 11 is a cross-section side view showing the adhesive
layers of FIG. 10 attached to a FB-DIMM type memory module
assembly.
[0028] FIG. 12 is a perspective view showing a heat treatment
fixture according to another embodiment of the present
invention.
[0029] FIG. 13 is a flow diagram showing a process for
manufacturing FB-DIMM type memory module assemblies according to
another embodiment of the present invention.
[0030] FIG. 14 is a top view showing a memory module assembly
according to another embodiment of the present invention.
[0031] FIG. 15 is a top view showing a conventional memory module
PCBA.
DETAILED DESCRIPTION
[0032] The present invention relates to improvements in memory
module assemblies (i.e., a memory module printed circuit board
assembly (PCBA) and one or more heat-sink plates). The following
description is presented to enable one of ordinary skill in the art
to make and use the invention as provided in the context of a
particular application and its requirements. Various modifications
to the preferred embodiment will be apparent to those with skill in
the art, and the general principles defined herein may be applied
to other embodiments. Therefore, the present invention is not
intended to be limited to the particular embodiments shown and
described, but is to be accorded the widest scope consistent with
the principles and novel features herein disclosed.
[0033] FIGS. 1(A) to 5 show a memory module assembly 100 according
to a simplified embodiment of the present invention. Memory module
assembly 100 generally includes a memory module PCBA 110 and one or
more heat-sink plates 130 and 140. FIGS. 1(A) and 1(B) are exploded
perspective and assembled perspective views, respectively, showing
the basic components of memory module assembly 100. FIG. 2 is a top
view showing memory module PCBA 110 by itself, and FIG. 3 is a top
plan view showing heat-sink plate 130 by itself. FIGS. 4(A) and
4(B) are top and cross-sectional side views, respectively, showing
heat-sink plates 130 and 140 mounted on memory module PCBA 110.
Finally, FIG. 5 is a cross-sectional end view taken along section
line 5-5 of FIG. 4(A). Although the embodiment described below
utilizes two heat-sink plates (i.e., plates 130 and 140) mounted
onto opposite sides of memory module PCBA 110, unless otherwise
specifically recited in the appended claims, only one heat-sink
plate (i.e., plate 130 or plate 140) may be attached to only one
side of memory module PCBA 110 in the manner described below.
[0034] Referring to FIGS. 1(A) and 2, memory module PCBA 110
includes a printed circuit board (PCB) substrate 111 having an
upper (first) surface 112 and an opposing lower (second) surface
113, and several integrated circuit (IC) memory devices (e.g.,
dynamic-random-access memory (DRAM) devices) 120-1 and/or 120-2
that are mounted on at least one of the upper and lower surfaces.
PCB substrate 111 includes a network of wiring traces 114 (shown in
FIG. 2) that are formed on at least one of upper surface 112 and
lower surface 113, and extend through layers of insulating material
(e.g., FR4) according to known manufacturing techniques. Selected
wiring traces 114 are connected between contact leads 121 of
selected memory devices 120 and associated contact pads 115 that
are arranged in a row along a lower (connector) edge 116 on both
surfaces 112 and 113 of PCB substrate 111. Metal contact pads 115
facilitate pluggable connection of memory module assembly 100 into
a host system (e.g., a PC or other computer system) to increase
available memory capacity by way of memory devices 120. Referring
to FIG. 5, when memory module assembly 100 is mounted into a host
system 500, metal contact pads 115 mate with pads 515 on a module
socket 510 to electrically connect the module to the host system's
motherboard 501. Optional side edge notches 117S, holes 117H, and
connector edge notch 117C are provided along side edges 118 and
connector edge 116 to ensure that the module is correctly
positioned in the socket. Upper edge 119 is located opposite to
connector edge 116.
[0035] Although generally referred to herein as memory devices, IC
devices 120-1 and 120-2 (collectively referred to as IC devices
120) may include one or more additional control IC devices, such as
a processor, an application specific integrated circuit (ASIC),
and/or a programmable logic device (PLD). Further in addition to IC
devices 120, additional electrical and electronic components 124
(shown in FIG. 1(A)), such as capacitors and inductors, may be
included on PCB substrate 111 using known techniques.
[0036] According to an embodiment of the invention, each memory
device is packaged such that its upper surface is planar (e.g.,
Thin Small Outline Package (TSOP)), and is maintained such that
each planar upper surface is parallel to PCB substrate 111. For
example, as shown in FIG. 1(A), each memory device 120-1 is mounted
on upper surface 112 such that its planar upper surface 122 is
maintained parallel to upper surface 112. Similarly, each memory
device 120-2 is mounted on lower surface 113 such that its planar
upper surface 126 is maintained parallel to lower surface 113.
[0037] Referring to FIGS. 1(A) and 3, heat-sink plates 130 and 140
are metal structures formed, for example, from a suitable sheet
metal (e.g., copper, aluminum, stainless steel or a metal alloy).
As indicated in FIG. 1(A), in one embodiment, heat-sink plate 130
includes a flat peripheral region 131 surrounding a depressed
(indented) planar outer surface 133, and a planar underside surface
134 formed on the outside (convex, lower facing) surface opposed to
planar outer surface 133. Similarly, heat-sink plate 140 includes a
flat peripheral region 141 surrounding a depressed (indented)
planar outer surface 143, and a planar underside surface 144 formed
on the inside (upward facing) surface opposed to outside surface
143. Underside surfaces 134 and 144 are secured in the manner
described below to one or more associated memory devices 120. Note
that, as indicated in FIG. 4(B), depression regions defined by
planar surfaces 133/143 are formed such that the footprint of these
regions encloses all of IC devices 120 (i.e., such that planar
underside surfaces 134/144 contact all of upper surfaces 122/126 of
IC devices 120-1/120-2). As shown in FIG. 3, one or both heat-sink
plates (e.g., plate 130) may include one or more slots S for heat
dissipation. Each heat-sink plate 130/140 has a lower edge
137L/147L, side edges 137S/147S, and an upper edge 137U/147U. In
addition, as shown in FIG. 3, the side edges of each plate are
modified to expose the notches formed in PCB substrate 111 (e.g.,
plate 130 includes a groove 137S for exposing side notches 117S, as
indicated in FIG. 4(A)).
[0038] As indicated in FIGS. 1(B), 4(A), 4(B) and 5, when heat-sink
plates 130/140 are mounted onto memory module PCBA 110, heat-sink
plates 130/140 substantially overlap PCB surfaces 112/113 in such a
way that IC devices 120 are protected, but contact pads 115 are
exposed for pluggable insertion of contact pads 115 into host
socket 510 (shown in FIG. 5). For example, as indicated in FIGS.
4(A) and 5, lower edges 137L/147L of heat-sink plates 130/140 are
aligned above connector edge 116 of PCB substrate 111 such that
contact pads 115 extends below lower edges 137L/147L of heat-sink
plates 130/140, and upper edges 137U/147U of heat-sink plates
130/140 protrude above upper edge 119 of PCB substrate 111.
Referring to FIG. 5, an opening (gap) G is provided between
heat-sink plates 130/140 and PCB substrate 111 adjacent to upper
edges 137U/147U to allow air heated by IC devices 120-1 and 120-2
to escape. Note that side edges 137S/147S and upper edges 137U/147U
of heat-sink plates 130/140 may be bent inward/downward to narrow
the space therebetween (e.g., gap G) to provide a better protection
for the electronic components from potential dust contamination,
but this may reduce air flow. The upward air flow (e.g., as
indicated by dashed arrows in FIG. 5) induced by free convection
will enhance heat dissipation from IC devices 120-1/120-2, and thus
reduce the operating temperature of memory module assembly 100. Of
course, in addition to the heat dissipated by free convection in
the generally upward directions, heat is also dissipated to the
surrounding air from the external surfaces of heat-sink plates
130/140 by free convection and radiation.
[0039] Referring to FIGS. 1(A), 1(B), 4(A), 4(B) and 5, according
to the present invention, adhesive portions 150 are applied to
planar upper surfaces 122/126 of selected memory devices
120-1/120-2 and/or to planar underside surfaces 134/144 of
heat-sink plates 130/140, and are then sandwiched therebetween in a
manner that secures heat-sink plates 130/140 to memory module PCBA
110. For example, as indicated in FIG. 1(B), a discrete adhesive
portion 150-1 (shown in dashed lines) is sandwiched between planar
underside surface 134 of heat-sink plate 130 and upper surface 122
of an associated IC device 120-11 (also shown in dashed lines) such
that heat-sink plate 130 is secured to memory module PCBA 110 by
adhesive portion 150-1. Similarly, a second discrete adhesive
portion 150-2 is sandwiched between planar underside surface 144 of
heat-sink plate 140 and upper surface 126 of an associated IC
device 125-21 (also shown in dashed lines) such that heat-sink
plate 140 is secured to memory module PCBA 110 by adhesive portion
150-2. By securing heat-sink plates 130/140 to memory module 110
using adhesive portions 150 instead of fasteners, the manufacturing
process for producing memory module assemblies 100 is greatly
simplified, and in addition tampering (i.e., removal of heat-sink
plates 130/140 to access IC devices 120/125) is more reliably
prevented and more easily detected.
[0040] According to an embodiment of the present invention,
adhesive portions 150 comprise heat-activated adhesive that is
applied to either upper surfaces 122/126 of one or more IC devices
120-1/120-2, or to the planar underside surfaces 134/144 of
heat-sink plates 130/140. In this embodiment, the heat-activated
adhesive 150 is softened (i.e., exhibits a relatively low
adherence) when heated to a high temperature (i.e., equal to or
less than the maximum operating temperature of the memory module
assembly), and the heat-activated adhesive exhibits a high
adherence when subsequently cooled. The advantage of such
heat-activated adhesives is that they can be removed by heating,
and thus enable reworking. In this case, subsequent removal of the
heat-sink plates from the memory module PCBA requires reheating at
a predetermined temperature to reflow the adhesive. Heat-activated
adhesives of this type are typically produced in the form of thin
film or tape can be used for IC devices that generate less heat,
and the main purpose of heat-sink plates 130/140 is thus relegated
to mainly protecting the IC devices. Such heat-activated adhesive
material forms a thin and continuous layer between the heat-sink
plate and the upper external surface of the IC devices. As the
newly formed interface layer is thin and can be made substantially
void-free (i.e., very few air bubbles), the thermal resistance
through the adhesive layer is relatively small. The ability to
rework, for example through heating, becomes an important
consideration. Thermoplastic based adhesive material such as
thermal bonding film (e.g., product numbers TBF615, TBF668)
produced by 3M of St. Paul Minn., or hot melt film (e.g., product
number 7802) produced by Henkel Loctite Corp. (Industrial) of Rocky
Hill Conn. can be used as an adhesive in this application.
[0041] While heat-activated adhesives provide an advantage in that
they can be reworked by reheating, such adhesives typically exhibit
relatively low thermal conductivity, thus making them less
desirable in applications that require a high level of heat
dissipation through the heat-sink plates.
[0042] In another embodiment, adhesive portions 150 comprise an
adhesive material that is "cured" during a heating process (i.e.,
exhibits an initial, relatively low adherence when applied, and a
relatively high adherence after being heat-cured). Such heat-cured
adhesives typically exhibit relatively high thermal conductivity
relative to heat-activated adhesives, and are therefore more
desirable in applications that require a high level of heat
dissipation through the heat-sink plates. The heat-cured adhesive
material is applied in the form of paste, and is re-distributed
under heat and pressure during curing to bond the IC devices and
heat-sink plates together. The curing process takes place at
elevated temperature, and can be expedited with the use of
activator. The re-distribution process causes the adhesive material
to flow and fill the void between the heat sink plate and memory
surface, resulting in a thin, good contact therebetween that
reduces thermal resistance from the heat source (IC device) to the
heat-sink plate. A dispensing machine can be used to ensure even
distribution of the adhesive material. In one embodiment, the
heat-cured adhesive consists of silicone elastomer-based resin for
re-workability and survivability at elevated temperature that the
electronic components may encounter. Metallic fillers may be added
to improve thermal conductivity. On suitable heat-cured adhesive is
provided by Dow Corning (e.g., product number 3-6752). Such
adhesives are removed using solvent to enable rework.
[0043] Although heat-activated and heat-cured adhesive materials
provide superior connection between the heat-sink plates and memory
module PCBA, it is also possible to use other types of adhesives in
the manner described herein to provide suitable connections.
Therefore, unless otherwise specified in the appended claims, the
term "adhesive portion" is intended to include any non-corrosive
adhesive that can reliably connect the heat-sink plates and memory
module PCBAs described herein.
[0044] In addition, although the present invention is described
above with certain benefits associated with attaching heat-sink
plates 130 and 140 to memory module PCBA 110 solely by adhesive
portions 150, in some embodiments an optional fastener (e.g., a
screw 160, rivet or clamp, which is shown in dashed lines in FIG.
1(B)) or clip may be utilized to provide a more sturdy and reliable
engagement arrangement. Exemplary embodiments utilizing low-profile
clips are described below with reference to FIGS. 6(A) to 8(C).
[0045] The embodiment described above with reference to FIGS. 1(A)
to 5 includes heat-sink plate edge features that maximize cooling
efficiency by allowing essentially unimpeded airflow under the heat
sink plates (i.e., between the heat sink plates and the PCB
substrate). Even though the area between the heat sink and
substrate is small and mostly occupied by the IC (e.g., memory and
controller) devices, small gaps between adjacent pairs of IC
devices can channel air flow past the IC devices, directly cooling
the IC devices as well as cooling the heat sink plate from both the
underside surface and its larger, exposed top surface. The
inventors encourage this airflow through the tiny channels between
IC devices by maintaining openings (e.g., gap G shown in FIG. 5)
near the top edge of the memory module assembly. These openings
allow air to escape from between the PCB substrate and the heat
sink plates. Air enters the gaps between the heat sink and the PCB
substrate from the open bottom edge near the lower connector edge,
and flows between the memory devices and out the top-edge openings.
Stagnant air under the heat sink plates is thus reduced.
[0046] FIGS. 6(A) and 6(B) are exploded perspective and
cross-sectional side views showing a FB-DIMM-type memory module
assembly 100A according to another embodiment of the present
invention. Memory module assembly 100A includes an FB-DIMM printed
circuit board assembly (PCBA) 110A, a first heat-sink plate 130A
attached to PCBA 110A by adhesive portions 150A1, 150A2 and 155A,
and a second heat-sink plate 140A attached to PCBA 110A by an
adhesive portion 150A2.
[0047] Similar to PCBA 110 (described above), FB-DIMM PCBA 110A
includes a substrate 111A having opposing first and second surfaces
112A and 113A, and (first) wiring traces 114A1 connected to
associated metal contact pads 115A that are disposed along a
connector edge 116A of substrate 111A. In addition, several memory
(first IC) devices 120A (e.g., DRAM devices) which are mounted on
upper surface 112A and 113A. Memory devices 120A are arranged on
upper surface 112A in two groups: a first group 120A1 and a second
group 120A2. As in the previous embodiments, upper surfaces 122A of
devices 120A1 and 120A2 substantially define a first plane P1
(shown in FIG. 6(D)) that is parallel to first surface 112A of
substrate 111A. Memory devices 120A3 are arranged on lower surface
113A such that upper surfaces 126A of devices 120A3 substantially
define a plane P3 (shown in FIG. 6(D)) that is parallel to surface
113A.
[0048] FB-DIMM PCBA 110A differs from PCBA 110 in that it includes
an advanced memory buffer (AMB) device 180 disposed on the first
surface 112A between device groups 120A1 and 120A2. AMB devices
(e.g., produced by NEC Electronics of Japan) are recently developed
IC devices utilized to configure FB-DIMMs in a way that greatly
improves communications between FB-DIMM PCBA 110A and a host
system. In general, AMB device 180 is connected to "upstream" and
"downstream" serial links by way of traces 114A1, and is connected
to DRAM devices 120A1, 120A2 and 120A3 by way of the bus indicated
by dashed line 114A2. Serial data from the host memory controller
sent through the downstream serial link (southbound) is temporarily
buffered by AMB device 180, and then sent to DRAM devices 120A1,
120A2 and 120A3. The serial data contains the address, data and
command information given to the DRAM, converted in AMB 180 and
sent out to the DRAM bus. AMB 180 writes in and reads out from the
DRAM devices as instructed by the host system memory controller
(not shown). The read data is converted to serial data, and sent
back to the memory controller on the upstream serial link
(northbound). Other features and functions performed by AMB 180 are
known to those skilled in the art of producing memory modules.
[0049] As indicated in FIG. 6(D), features typical of AMB device
180 are that it has a taller profile than DRAM devices 120A1 and
120A2, and it is housed in a Ball Grid Array (BGA) package. In
particular, an upper surface 182 of AMB device 180 defines a
(second) plane P2 that is parallel to substrate surface 112A, and
is located above plane P1 defined by DRAM devices 120A1 and 120A2
(i.e., plane P1 is located between plane P2 and surface 112A). As
is understood in the art, BGA packaged devices are connected to
underlying substrates (e.g., PCB 111A) by way of solder or
solder-like connections that are relatively brittle (i.e., in
comparison to the pin-type connections utilized to mount DRAMs
120A1 and 120A2). These relatively brittle connections typically
require protection from mechanical shock to prevent cracking of the
connections that can result in electrical disconnection.
[0050] Similar to the embodiments described above, heat-sink plate
130A includes recessed regions 131A1 and 131A2 that respectively
include planar outer surfaces 133A1 and 133A2 and planar underside
surfaces 134A1 and 134A2, and these regions are secured to the
upper surfaces 122A of DRAM devices 120A1 and 120A2, respectively,
by way of thermal-bond adhesive film portions 150A1 and 150A2. In
particular, adhesive film portion 150A1 is sandwiched between
planar underside surface 134A1 and the upper surface 122A of DRAM
devices 120A1. Similarly, adhesive film portion 150A2 is sandwiched
between planar underside surface 134A2 and upper surfaces 122A of
DRAM devices 1202. Thus, heat-sink plate 130A is rigidly secured to
PCBA 110A by adhesive film portions 150A1 and 150A2 in a manner
similar to that described above. Similarly, lower heat-sink plate
140A includes a substantially planar underside surface 144A that is
secured by way of a thermal-bond adhesive film portion 150A3 to
upper surfaces 126A of DRAM devices 120A3, thereby securing lower
heat-sink plate 140A to PCBA 110A. When the IC memory chips are BGA
(Ball Grid Array) or CSP (Chip Scale Package), using epoxy
underfill to fortify the adhesion between IC chips and PCB package
increases the memory module's strength and reliability by providing
an additional protection against shock, vibration and bending
stiffness of the memory module.
[0051] In accordance with another aspect of the present invention,
in order to accommodate the taller profile of AMB device 180,
heat-sink plate 130A includes a raised pocket region 131A3 that is
disposed between recessed regions 131A1 and 131A2, and has a planar
underside surface 134A3 that is positioned above (i.e., further
from substrate 111A than) planar underside surfaces 134A1 and 134A2
(as indicated in FIG. 6(B)). Further, in order to minimize
mechanical shock while providing suitable heat transfer between AMB
device 180 and raised pocket region 131A3, thermal paste portion
155A is optionally disposed between the upper surface 182 of the
AMB device 180 and the planar underside surface 134A3. In one
embodiment, thermal compound 155A includes one of a thermal paste
produced by Vantec Thermal Technologies of Freemont, Calif. USA, a
silicone compound (SIL More, Taiwan), Chomerics pad, or Honeywell
PCM45F. In another embodiment (not shown), thermal paste portion
155A is omitted, and AMB device 180 is directly contacted by
underside surface 134A3 of upper heat-sink plate 130 for heat
dissipation.
[0052] Referring again to FIG. 6(A), FB-DIMM PCBA 110A further
differs from PCBA 110 in that, in addition to slots 117S1 formed on
side edges 118A that are similar to slots 117S described above,
substrate 111A also includes positioning notches 117S2 that are
utilized to properly align heat-sink plates 130A and 140A during
assembly in the manner described below.
[0053] In accordance with another aspect of the present invention,
when both heat-sink plate 130A and 140A are mounted onto PCBA 110B
(as indicated in FIGS. 6(B) and 6(C)), upper heat-sink plate 130A
and lower heat-sink plate 140A contact surfaces 112A and 113A,
respectively, adjacent to side edges 118A, thereby forming a rigid
frame that further protects AMB device 180 from mechanical shock.
In particular, as indicated in FIG. 6(A), heat-sink plate 130A
includes side wall structures 138A1 and tabs 138A2 that extend
downward from side wall structures 138A1. Conversely, lower
heat-sink plate 140A includes a side wall support structure 148A1
that defines a groove 148A2. As shown in FIGS. 6(B) and 6(C), when
mounted onto PCBA 110A, side wall structures 138A1 of upper
heat-sink plate 130A contact upper surface 112A adjacent to side
edges 118A, and side wall structures 148A1 of upper heat-sink plate
140A contact lower surface 113A adjacent to side edges 118A,
thereby sandwiching the outer side edge portions of PCBA 110A
between side wall structures 138A1 and 148A1. In addition, tabs
138A2 of heat-sink plate 130A extend from side wall structures
138A1 through notches 117S2, and are received in grooves 148A2
defined by side wall support structure 148A1 of lower heat-sink
plate 140A. This tab/groove arrangement facilitates reliable and
cost effective assembly by facilitating substantially foolproof
alignment of heat-sink plates 130A and 140A to PCBA 110A without
the need for manual adjustment. That is, heat-sink plates 130A and
140A can only be mounted onto PCBA 110A when tabs 138A2 extend
through notches 117S2 and are received in notches 148A2--any other
assembly arrangement will be immediately noticed due to the
improper orientation of plates 130A and/or 140A, and thus easily
corrected.
[0054] In accordance with yet another aspect of the present
invention, FB-DIMM-type memory module assembly 100A further
includes two single-piece clips 160A1 and 160A2 that are used to
press heat-sink plates 130A and 140A onto opposing surfaces 112A
and 113A of PCBA 110A, thus providing a more sturdy and reliable
engagement arrangement. The term "single-piece" is used herein to
indicate that clips 160A1 and 160A2 are produced from an integral
sheet of a suitable resilient material (e.g., spring steel) that
has been patterned, bent and/or otherwise formed using conventional
techniques to generate the desired shape. Each single-piece clip
160A1 and 160A2 is formed from such that, when mounted onto
heat-sink plates 130A and 140A in the manner shown in FIGS. 6(B) to
6(D), single-piece clips 160A1 and 160A2 press heat-sink plates
130A and 140A toward PCBA 110A, thereby sandwiching PCBA 110A
therebetween. Referring to the left side of FIG. 6(A), single-piece
clip 160A1 includes first and second linking members 161A1 and
161A2, a first engaging portion formed by side arms 162A1 and 162A2
and end portion 163A, and a second engaging portion formed by side
arms 165A1 and 165A2 and end portion 166A. Side arms 162A1 and
162A2 are connected at first ends to upper ends of first and second
linking members 161A1 and 161A2, respectively, and end portion 163A
extends between second ends of side arms 162A1 and 162A2.
Similarly, side arms 165A1 and 165A2 are connected at first ends to
lower ends of first and second linking members 161A1 and 161A2,
respectively, and end portion 166A extends between second ends of
side arms 1652A1 and 165A2. Single-piece clip 160A2 is
substantially identical to single-piece clip 160A1. Referring to
FIG. 6(B) to 6(D), when single-piece clip 160A1 is operably mounted
onto heat-sink plates 130A and 140A, side arms 162A1 and 162A2 and
end portion 163A are connected to outer surface portion 133A1 of
heat-sink plate 130A, side arms 165A1 and 165A2 and end portion
166A are connected to the second outer surface portion 143A1 of the
second heat-sink plate 140A, and side arms 1652A1 and 165A2 serve
to press these engaging portions against heat-sink plates 130A and
140A. Single-piece clip 160A2 is mounted in a similar manner onto
outer surface portions 133A2 and 143A2, thereby securing PCBA 110A
between heat-sink plates 130A and 140A. In addition to the integral
portions described above, single-piece clips 160A1 and 160A2 may
include additional, non-integral structures (e.g., wire levers
similar to those found on a binder clip).
[0055] In accordance with another aspect of the present invention,
heat-sink plates 130A and 140A respectively include hooks 132A1,
132A2, 142A1 and 142A2 for reliably securing single-piece clips
160A1 and 160A2 onto heat-sink plates 130A and 140A. As indicated
in FIG. 6(A), hooks 132A1 protrude from outer surface portion 133A1
of heat-sink plate 130A, and hooks 132A2 protrude from outer
surface portion 133A2. Similarly, hooks 142A1 protrude from outer
surface portion 143A1 of heat-sink plate 140A, and hooks 142A2
protrude from outer surface portion 143A2. Single-piece clip 160A1
is constructed such that, when operably mounted onto heat-sink
plates 130A and 140A, end portion 163A engages hooks 132A1, and end
portion 166A engages hooks 142A1. Similarly, clip 160A2 engages
hooks 132A2 and 142A2. Thus, when both heat-sink plate 130A and
140A are mounted onto PCBA 110A and clips 160A1 and 160A2 are
engaged (as indicated in FIGS. 6(B) and 6(C)), upper heat-sink
plate 130A and lower heat-sink plate 140A are reliably and rigidly
held against surfaces 112A and 113A, respectively, adjacent to side
edges 118A, thereby forming a rigid frame that further protects AMB
device 180 from mechanical shock.
[0056] FIGS. 7(A), 7(B) and 7(C) are exploded perspective and
assembled perspective views showing a FB-DIMM-type memory module
assembly 100B according to another embodiment of the present
invention. Memory module assembly 100B includes an upper heat-sink
plate 130B, a lower heat-sink plate 140B, and a single-piece clip
160B. Omitted from FIG. 7(A) for clarity are FB-DIMM PCBA 110A
(discussed above) and adhesive portions that are mounted between
opposing sides of PCBA 110A and upper heat-sink plate 130B and
lower heat-sink plate 140B, respectively, in the manner described
above. Similar to the structure described above, upper heat-sink
plate 130B includes first and second recessed portions 131B1 and
131B2 that are separated by a raised pocket structure 131B3. Single
piece clip 160B is attached to upper heat-sink plate 130B and lower
heat-sink plate 140B, and heat-sink plate 130B and 140B are
attached to PCBA 110A in a manner similar to the method described
above with the following exceptions.
[0057] First, heat-sink plates 130B and 140B include side wall
structures 132B1 and 142B1 that are similar to those of heat-sink
plates 130A and 140A, but instead of including a single tab that
extends the entire length of groove 117S2, heat-sink plate 130A and
140A includes shorter tab portions 138B2 and 148B2, respectively,
that extend partially into groove 117S2 as shown in FIGS. 7(B) and
7(C). Tab portions 138B2 and 148B2 function to align heat-sink
plates 130B and 140B during assembly in a manner similar to that
provided by the full length tab associated with memory module
assembly 100A (described above).
[0058] Second, memory module assembly 100B differs from memory
module assembly 100A in that it utilizes a single single-piece clip
160B to press and secure heat-sink plates 130B and 140B onto PCBA
110A. In particular, a first hook 132B1 is formed on upper surface
portion 133B1 of first recessed region 131B1, and a second hook
132B2 is formed on upper surface portion 133B2 of second recessed
region 131B2. Single-piece clip 160B includes a first engaging
portion 163B1 disposed on a first side arm 162B1, a second engaging
portion 163B2 disposed on a second side arm 162B2, and linking
members 161B1 and 161B2 respectively connected between side arms
162B1 and 162B2 and a lower (second) engaging portion formed by
lower side arms 165B1 and 165B2 and an end portion 166B. When
single-piece clip 160B is mounted onto heat-sink plates 130B and
140B, first engaging portion 163B1 is connected to first hook 132B1
on a first side of raised pocket structure 131B3, and second
engaging portion 163B2 is connected to second hook 132B2 on the
opposite side of raised pocket structure 131B3, thereby providing a
uniform pressing force using a single clip.
[0059] FIGS. 8(A), 8(B) and 8(C) are exploded perspective and
assembled perspective views showing a FB-DIMM-type memory module
assembly 100C according to another embodiment of the present
invention. Omitted from FIG. 8(A) for clarity are FB-DIMM PCBA 110A
(discussed above) and adhesive portions that are mounted between
opposing sides of PCBA 110A and upper heat-sink plate 130C and
lower heat-sink plate 140C, respectively, in the manner described
above. Similar to the structure described above, upper heat-sink
plate 130C includes first and second recessed portions 131C1 and
131C2 that are separated by a raised pocket structure 131C3. Upper
heat-sink plate 130C and lower heat-sink plate 140C are attached to
FB-DIMM PCBA 110A by single-piece clip 160C in a manner similar to
the method described above with reference to FIGS. 7(A) to 7(C)
except in the manner in which single-piece clip 160C is secured to
heat-sink plates 130C and 140C. In particular, instead of hooks, a
first slot 132C1 is defined in a first side edge of raised pocket
structure 131C3, a second slot 132C2 is defined in the opposite
side edge of raised pocket structure 131C3, and lower heat-sink
plate 140C defines a pair of holes 142D1 and 142D2. In addition,
single-piece clip 160C includes a first engaging portion 163C1
disposed on a first side arm 162C1, a second engaging portion 163C2
disposed on a second side arm 162C2, and linking members 161C1 and
161C2 respectively connected between side arms 162C1 and 162C2 and
a lower (second) engaging portion formed by lower side arms 165C1
and 165C2 and an end portion 166C. Positioning pins 167C1 and 167C2
protrude upward from end portion 166C. When single-piece clip 160C
is mounted onto heat-sink plates 130C and 140C, first engaging
portion 163C1 is inserted into first slot 132C1 on a first side of
raised pocket structure 131C3, second engaging portion 163C2 is
inserted into second hook 132C2 on the opposite side of raised
pocket structure 131C3, and positioning pins 167C1 and 167C2 are
inserted into holes 142C1 and 142C2, respectively, thereby reliably
securing clip 160C to heat-sink plates 130C and 140C.
[0060] Several other embodiments are contemplated by the inventors.
For example the heat sink may be made from a variety of
heat-conducting materials such as aluminum, aluminum alloy, copper,
brass, bronze, stainless steel, etc.
[0061] In addition, the adhesive arrangements utilized in the
embodiments described above are intended to be exemplary, and may
be altered to facilitate better adherence and/or heat transfer
characteristics of the resulting memory module assembly. For
example, FIG. 9 shows upper and lower thermal paste layers 150E1
and 150E2 that may be respectively disposed between the heat-sink
plates and PCBA in accordance with an alternative embodiment.
Alternatively, as shown in FIGS. 10 and 11, a laminated adhesive
structure 150F may be utilized to secure, for example, IC devices
120 to upper heat-sink plate 130. In the disclosed embodiment,
laminated adhesive structure 150F includes a lower adhesive film
152, an upper adhesive film 154, and a thermal paste layer 156
disposed between the upper and lower adhesive films.
[0062] FIG. 12 is a perspective view showing a heat-sink reflow
fixture 1200 utilized in a process for assembling FB-DIMM memory
modules 100 according to another embodiment of the present
invention. The memory modules assembled using fixture 1200 may
include any of the modules described in the embodiments set forth
above. Fixture 1200 includes a base 1205 defining a plurality of
recesses 1210 for receiving FB-DIMM memory modules 100 in the
depicted manner. Two spring clamps 1220 are mounted onto base 1205
and include adjustment screws 1225 that, when turned, press contact
points 1227 against heat-sink plate 130 or heat-sink plate 140 of
memory module 100, thereby securing memory module 100 in a fixed
manner for heat treatment. Although four recesses 1210 are shown,
the number of recesses may be increased or decreased to maximize
the efficiency of the heat treatment process.
[0063] FIG. 13 is a flow diagram showing a process of assembling
FB-DIMM memory modules 100 utilizing heat-sink reflow fixture 1200
of FIG. 12. In block 1310, the various IC devices (e.g., memory
devices and AMB devices) and other components are mounted onto the
PCB substrate to form the memory module PCBA (e.g., PCBA 110,
discussed above). In block 1320, one or more of the adhesive
portions describe above are applied to the upper and lower
heat-sink plates (e.g., heat-sink plates 130 and 140). The adhesive
can be applied to the heat-sink surface by manual or automatic
using dispensing machine. Next, immediately after dispensing the
adhesive, the upper and lower heat-sink plates are mounted and
aligned onto the memory module PCBA to form a memory module
assembly using the methods described above (block 1330). In block
1340, the memory module assembly are mounted and secured by spring
clamps 1220 into a corresponding recess 1210 of fixture 1200, and
then the fixture is passed through an oven or otherwise subjected
to an appropriate temperature (i.e., at or lower than the maximum
safe operating temperature for the memory module components, e.g.,
80.degree. C. for approximately 15 minutes) to activate and/or cure
the adhesive material. Finally, in block 1350, the memory module
assembly is allowed to cool and is then removed from fixture 1200.
For subsequent re-work to separate the PCBA from the heat-sink
plates, the memory module assembly may be subjected to a
temperature of about 150.degree. C. for several seconds to remove
the adhesives.
[0064] FIG. 14 is a modified top view showing a memory module
assembly 100K according to yet another embodiment of the present
invention. Memory module assembly 100K differs from previously
described embodiments in that it includes a memory module PCBA 110K
that is in the form of a Small Outline Dual Inline memory Module
(SODIMM). This type of memory module is used mostly for notebook
computers, with Thin Small Outline Package (TSOP). The number of
memory devices 120K is typically reduced in half, with each side of
memory module assembly 100K including a row of up to four devices.
Adhesive is applied according to the previously described
embodiments to the memory devices or the inside of the heat-sink
plates (e.g., heat sink plate 130K), before the heat sink plates
are attached to the memory module PCBA 110K. All the other features
of memory module assembly 100K are similar to those described
above. Further, in addition to the SODIMM arrangement shown in FIG.
12, the present invention may be incorporated into memory module
assemblies including any of a Single Inline Memory Module (SIMM)
device, a Dual Inline Memory Module (DIMM) device, and a Small
Outline DIMM (SODIMM) device.
[0065] Terms such as "upper edge", "side edge", "lower edge",
"front surface", "outer surface" and "underside surface" are
arbitrarily assigned as shown in the figures and each term could
refer to either surface of the module and/or heat-sink structure.
Vias of through-holes may provide electrical connection between the
surfaces or intermediate layers. These through-holes could be
filled in holes or metal traces between layers rather than open
holes, and can also be formed during the PCB processing as an
integral part of the PCB. Various alternatives in geometries of the
heat-sink plates and memory modules could be substituted.
[0066] The foregoing description of the embodiments of the
invention has been presented for the purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed. Many modifications and
variations are possible in light of the above teaching. It is
intended that the scope of the invention be limited not by this
detailed description, but rather by the claims appended hereto.
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