U.S. patent application number 16/405614 was filed with the patent office on 2019-08-29 for adhesive-bonded thermal interface structures.
The applicant listed for this patent is International Business Machines Corporation. Invention is credited to Mark K. Hoffmeyer, Phillip V. Mann, Karl Stathakis.
Application Number | 20190267254 16/405614 |
Document ID | / |
Family ID | 64692701 |
Filed Date | 2019-08-29 |
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United States Patent
Application |
20190267254 |
Kind Code |
A1 |
Stathakis; Karl ; et
al. |
August 29, 2019 |
ADHESIVE-BONDED THERMAL INTERFACE STRUCTURES
Abstract
A heat sink can be attached to a heat-producing electronic
device by aligning an adhesive material to a surface of the heat
sink, applying the adhesive material to the surface to form an
outer perimeter and applying, within the outer perimeter, a
thermally conductive material to the surface. The surface of the
heat sink and a surface of the heat-producing electronic device can
then be aligned, and the heat sink can be assembled to the
heat-producing electronic device by bringing the heat-producing
electronic device surface into contact with the adhesive material.
The heat sink can then be affixed to the heat-producing electronic
device by applying a compressive force to the assembly to activate
the adhesive material.
Inventors: |
Stathakis; Karl; (Owatonna,
MN) ; Mann; Phillip V.; (Rochester, MN) ;
Hoffmeyer; Mark K.; (Rochester, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
International Business Machines Corporation |
Armonk |
NY |
US |
|
|
Family ID: |
64692701 |
Appl. No.: |
16/405614 |
Filed: |
May 7, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15629171 |
Jun 21, 2017 |
10319609 |
|
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16405614 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 23/3736 20130101;
H01L 21/56 20130101; H01L 21/76 20130101; H01L 23/24 20130101; H01L
23/367 20130101; H01L 23/373 20130101; H01L 23/42 20130101 |
International
Class: |
H01L 21/56 20060101
H01L021/56; H01L 23/373 20060101 H01L023/373; H01L 21/76 20060101
H01L021/76; H01L 23/367 20060101 H01L023/367; H01L 23/42 20060101
H01L023/42; H01L 23/24 20060101 H01L023/24 |
Claims
1. A method for attaching a heat sink to a electronic device, the
heat sink having a first surface, the heat-producing electronic
device having a second surface, the heat sink including a
protrusion extending away from the heat sink, the method
comprising: applying an adhesive material to the first surface to
form an outer perimeter; applying, within the outer perimeter, a
thermally conductive material to the first surface, the thermally
conductive material contained within the outer perimeter, the first
surface, and the second surface; assembling the heat sink to the
electronic device by bringing the second surface into contact with
the adhesive material; and activating the adhesive material by
applying a compressive force to the heat sink and to the
heat-producing electronic device.
2. The method of claim 1, wherein the adhesive material is a
pressure-sensitive adhesive (PSA).
3. The method of claim 1, wherein the applying of the thermally
conductive material to the first surface includes applying a
thermal interface material (TIM) pad to the first surface.
4. The method of claim 1, wherein the applying of the thermally
conductive material to the first surface includes an application,
to the first surface, of a tacking material configured to hold a
thermal interface material (TIM) pad adjacent to the first surface
during assembly of the heat sink to the heat-producing electronic
device.
5. The method of claim 1, wherein the adhesive material holds a
thermal interface material (TIM) pad adjacent to at least one of
the first surface and the second surface.
6. The method of claim 5, wherein the adhesive material is
thermally conductive and fills at least one gap between the TIM pad
and the at least one of the first surface and the second surface to
which the TIM pad is held adjacent.
7. The method of claim 1, wherein the applying of a thermally
conductive material to the first surface includes an application of
a formable thermal conductive material selected from the group
consisting of a thermal grease, a thermal paste, a thermal gel and
a phase-change material.
8. The method of claim 1, wherein the activating the adhesive
material includes an adhesive material curing process.
9. The method of claim 8, wherein the adhesive material curing
process causes a contraction of the adhesive material, the
contraction providing a tensile force between the first surface and
the second surface.
10. The method of claim 1, wherein, once activated, the adhesive
material holds the first surface in an adjacent, coplanar
orientation to the second surface such that an outer cavity is
formed, wherein the outer cavity is bounded by the outer perimeter,
the first surface and the second surface, wherein a thermally
conductive material is contained in an inner cavity enclosed within
the outer cavity, the inner cavity bounded by an inner perimeter,
the first surface and the second surface, and wherein the thermally
conductive material is configured to cool the heat-producing
electronic device by providing a thermally conductive path between
the first surface and the second surface.
11. The method of claim 10, wherein the first surface includes a
protrusion that extends away from the first surface, the protrusion
defining the inner perimeter on the first surface.
12. The method of claim 11, wherein a first height of the
protrusion, extending away from the first surface, is in a range
between 25% and 95% of a second height of the adhesive
material.
13. The method of claim 11, wherein an outline of the adhesive
material defines a vent formed between the inner perimeter and an
exterior perimeter of the adhesive material.
14. The method of claim 1, wherein a first height of the
protrusion, extending away from the heat sink, is in a range
between 40% and 90% of a second height of the adhesive
material.
15. The method of claim 1, wherein a first height of the
protrusion, extending away from the heat sink, is less than a
distance, in an assembled configuration, between the first surface
and the second surface.
16. The method of claim 1, wherein the adhesive material is
thermally conductive and configured to transfer heat between the
second surface and the first surface.
17. The method of claim 1, wherein the adhesive material is
chemically inert with respect to the thermally conductive
material.
18. The method of claim 1, wherein an outline of the adhesive
material defines a vent formed between spatial confines defined by
the outer perimeter and an exterior perimeter of the adhesive
material.
19. The method of claim 1, wherein a thermally conductive material
is positioned, in an unassembled configuration, at a perimeter of a
thermal interface material (TIM) pad, the TIM pad located within
spatial confines defined by the outer perimeter, the first surface,
and the second surface, the thermally conductive material
positioned, in an assembled configuration, between the TIM pad and
at least one of a portion of the first surface and a portion of the
second surface.
20. The method of claim 19, wherein the adhesive material is
thermally conductive and is positioned, in the assembled
configuration, between the TIM pad and at least one of a portion of
the first surface and a portion of the second surface.
Description
BACKGROUND
[0001] The present disclosure generally relates to transferring
heat generated by electronic devices. In particular, this
disclosure relates to using an adhesively bonded thermal interface
structure to remove heat from an electronic device.
[0002] A thermal interface material (TIM) can be used to enhance
heat transfer, through reducing the thermal resistance between an
electronic device such as an integrated circuit (IC) and a heat
sink. Types of TIMs can include, but are not limited to, thermal
greases, adhesives, pads and gap fillers. TIMs can include
thermally conductive solids and particulate fillers which can be
mixed with a binding agent such as a silicone or polymer compounds.
A TIM can enhance thermal conductivity by filling irregularities
and air gaps between adjacent, mating surfaces, for example, of the
IC and the heat sink, with a thermally conductive material.
[0003] A heat sink may be used in computers and electronic systems
as a passive heat exchanger, and may act as a reservoir that can
absorb an arbitrary amount of heat without significantly changing
temperature. Heat sinks may be used in computers, for example, to
cool devices such as central processing units (CPUs) and/or
graphics processing units (GPUs). Heat dissipation from a heat sink
can be accomplished through convection, radiation, or conduction,
into an ambient or circulated medium, such as air, water, or a
coolant/refrigerant. Heat sinks reach a temperature greater than a
cooling medium, in order to transfer heat across a thermal gradient
from an electronic device to the medium.
SUMMARY
[0004] Embodiments may be directed towards a method for attaching a
heat sink to a heat-producing electronic device. One of the heat
sink and the heat-producing electronic device may have a first
surface, the other of the heat sink and the heat-producing
electronic device may have a second surface. The method can include
aligning an adhesive material to the first surface and applying the
adhesive material to the first surface to form an outer perimeter.
The method can also include applying, within the outer perimeter, a
thermally conductive material to the first surface, aligning the
second surface to the first surface, and assembling the heat sink
to the heat-producing electronic device by bringing the second
surface into contact with the adhesive material. The method can
also include affixing the heat sink to the heat-producing
electronic device by applying a compressive force to the heat sink
and to the heat-producing electronic device, the compressive force
activating the adhesive material.
[0005] Embodiments may also be directed towards an apparatus for
cooling a heat-producing electronic device. The apparatus can
include a heat sink with a first surface having a protrusion
extending away from the first surface, the protrusion defining an
inner perimeter on the first surface. The apparatus can also
include an adhesive material affixed to the first surface and to a
second surface of the heat-producing electronic device. The
adhesive material can hold the first surface of the heat sink in an
adjacent, coplanar orientation to the second surface of the
heat-producing electronic device. The adhesive material can define
an outer perimeter on the first and second surfaces and form an
outer cavity bounded by the outer perimeter, the first surface and
the second surface. The apparatus can also include a thermally
conductive material contained in an inner cavity enclosed within
the outer cavity. The inner cavity can be bounded by the inner
perimeter, the first surface and the second surface. The thermally
conductive material can be configured to cool the heat-producing
electronic device by providing a thermally conductive path between
the first surface and the second surface.
[0006] Embodiments may also be directed towards an apparatus for
cooling a heat-producing electronic device. The apparatus can
include a heat sink having a first surface and an adhesive material
affixed to the first surface and to a second surface of the
heat-producing electronic device. The adhesive material can hold
the first surface in an adjacent, coplanar orientation to the
second surface. The adhesive material, in an unassembled
configuration, can define a perimeter on the first and second
surfaces and form a cavity bounded by the perimeter, the first
surface and the second surface. The apparatus can also include a
thermal interface material (TIM) pad located within the cavity. The
TIM pad can be configured to cool the heat-producing electronic
device by providing a thermally conductive path between the
heat-producing electronic device and the heat sink. The thermally
conductive path can include at least a portion of a third surface
of the TIM pad in thermally conductive contact with a corresponding
portion of the first surface of the heat sink and at least a
portion of a fourth surface of the TIM pad in thermally conductive
contact with a corresponding portion of the second surface of the
heat-producing electronic device.
[0007] The above summary is not intended to describe each
illustrated embodiment or every implementation of the present
disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The drawings included in the present application are
incorporated into, and form part of, the specification. They
illustrate embodiments of the present disclosure and, along with
the description, serve to explain the principles of the disclosure.
The drawings are only illustrative of certain embodiments and do
not limit the disclosure.
[0009] FIG. 1 depicts an apparatus for cooling a heat-producing
electronic device including a thermally conductive material
enclosed within an inner perimeter of a heat sink, according to
embodiments of the present disclosure.
[0010] FIG. 2 depicts an apparatus for cooling a heat-producing
electronic device including a thermally conductive pad enclosed
within a perimeter, according to embodiments consistent with the
figures.
[0011] FIG. 3 depicts an apparatus for cooling a heat-producing
electronic device including a thermally conductive pad and a
thermally conductive material enclosed within a perimeter,
according to embodiments consistent with the figures.
[0012] FIG. 4 depicts an apparatus for cooling a heat-producing
electronic device including a thermally conductive pad and a
thermally conductive adhesive, according to embodiments consistent
with the figures.
[0013] FIG. 5 includes a set of six consistent cross-sectional
views illustrating the results of process operations for attaching
a heat sink to an electronic device, according to embodiments
consistent with the figures.
[0014] FIG. 6 is a flow diagram depicting a method for attaching a
heat sink to an electronic device, according to embodiments
consistent with the figures.
[0015] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the
invention.
[0016] In the drawings and the Detailed Description, like numbers
generally refer to like components, parts, steps, and
processes.
DETAILED DESCRIPTION
[0017] Certain embodiments of the present disclosure can be
appreciated in the context of providing efficient heat transfer
between a heat-producing electronic device and a heat sink for
electronic equipment such as servers, which may be used to provide
data to clients attached to a server through a network. Such
servers may include, but are not limited to web servers,
application servers, mail servers, and virtual servers. While not
necessarily limited thereto, embodiments discussed in this context
can facilitate an understanding of various aspects of the
disclosure. Certain embodiments may also be directed towards other
equipment and associated applications, such as providing efficient
heat transfer between a heat-producing electronic device and a heat
sink for electronic equipment such as computing systems, which may
be used in a wide variety of computational and data processing
applications. Such computing systems may include, but are not
limited to, supercomputers, high-performance computing (HPC)
systems, and other types of special-purpose computers. Embodiments
may also be directed towards providing efficient heat transfer
between a heat-producing electronic device and a heat sink for
electronic equipment such as desktop workstations and computing
systems, which can include heat-producing electronic devices such
as graphics processing units (GPUs).
[0018] The term "heat-producing electronic device" is used herein
in reference to devices such as one or more integrated circuits
(ICs), and/or an electronic module which can include one or more
ICs or other electronic devices. A heat-producing electronic device
generates and dissipates heat in response to electrical power
consumed by the device. The terms "heat-producing electronic
device" and "electronic device" are used interchangeably herein
without loss of meaning.
[0019] For ease of discussion, the term "heat sink" is used herein
with reference to various devices used to transfer and dissipate
heat generated by heat-producing electronic devices. In the context
of the present discussion, the term "heat sink" can refer to and
include heat spreaders, heat pipe structures, and devices designed
to dissipate heat into cooling media such as ambient or circulated
air, cooling liquid, e.g., water, or refrigerant.
[0020] The terms thermal interface material ("TIM") and "TIM pad"
are used interchangeably herein with reference to various
commercially available thermally conductive pads used to transfer
heat from a heat-producing electronic device to a heat sink. TIM
pads can be fabricated from a variety of different thermally
conductive materials, e.g., carbon fibers, indium, copper and
silver. TIM pads can be used to enhance thermal conductivity by
filling in gaps and surface irregularities found on the mating
surfaces of a heat-producing electronic device and a heat sink. TIM
pads are generally thin, e.g., between 0.1 mm and 0.5 mm thick,
pre-formed, and can be fragile. Various TIM pads can have a range
of resiliency, in response to compressive forces, depending on the
physical properties of materials used to construct the TIM pad.
[0021] In the context of the present discussion, the terms
"copper," "aluminum" and "indium" and "silver" are used herein in
reference to highly thermally conductive materials, such as metals,
used in embodiments. It can be understood however that various
embodiments can also be useful with regards to metallic alloys
which may include copper, aluminum, indium, silver and/or other
thermally conductive materials.
[0022] The trends of decreasing dimensions of ICs, e.g., processor
chips, and increasing IC power dissipation have generally occurred
simultaneously, resulting in increased operating temperatures and
power densities of electronic devices. These converging trends have
highlighted the importance of providing an efficient thermal
interface between a heat-producing electronic device such as an IC
or multi-IC electronic module and a cooling device such as a heat
sink. Such an efficient thermal interface can be effective in
maintaining the electronic device's operating temperature within a
specified operating range.
[0023] In order for a thermal interface to be effective in
transferring heat from a heat-producing electronic device, it may
need to possess a number of attributes. Such attributes can include
high thermal conductivity, and the ability to fill surface
irregularities/gaps between heat-producing electronic device and
heat sink surfaces, while being relatively compliant and
compressible under the application of a relatively low compression
force. An effective thermal interface can also be stable and
reliable over time and/or repeated thermal cycles, and should not
manifest "grease pumping" or thermal interface material
displacement/voiding resulting from electronic device and/or heat
sink thermally-induced flexing. A robust thermal interface can be
durable within "shock and vibration" environments, and constructed
from materials that are chemically inert with respect to each
other. A desirable thermal interface can have a relatively
low-cost, simple and straightforward implementation involving
minimal surface preparation requirements, processing/material
handling issues, and may require no latching hardware to attach the
heat sink to the heat-producing electronic device.
[0024] A number of materials can be used to construct a thermal
interface between a heat-producing electronic device and a heat
sink. While each of these materials can possess attributes
beneficial to thermal interface construction, each of them may also
have characteristics that can contribute to the thermal interface's
premature failure and/or degrade its performance. For example, in
some applications, thermal compounds known as "thermal greases" can
provide low-cost, high thermal conductivity gap filling for
relatively large and/or variable gaps between a heat-producing
electronic device and a heat sink. Thermal greases can, however, be
subject to "grease pumping" or displacement over time and/or a
number of thermal cycles, which can significantly reduce the
effectiveness of the thermal interface. Thermal compounds known as
"thermal gels" can provide robust gap-filling capability and high
thermal conductivity; however, thermal gels can require complicated
and expensive surface preparations and material storage/handling in
order to ensure long-term material adhesion and thermal
performance. Thermal gels can also be sensitive to degradation
within "shock and vibration" environments. TIM pads can provide
high thermal conductivity and be relatively easy to implement,
however, TIM pads can also have limited compressibility and
gap-filling capability within a compressive loading range that is
safe for certain interface applications including an IC die with an
exposed face. Various soft thermal gap-filler materials can also be
used within thermal interfaces; however these materials generally
offer relatively low thermal conductivity, rendering them
unsuitable for high-output heat-producing electronic devices such
as a processor or GPU. Various phase-change thermal materials can
offer gap-filling with limited grease-pumping characteristics,
however the phase-change properties of these materials can fail
over time, in addition to phase-change material leakage from the
thermal interface. Liquid metal thermal materials can offer high
thermal conductivity gap-filling, however such materials are
relatively costly, can leak from thermal interfaces, and can
adversely react with other thermal interface components, causing
catastrophic thermal interface and component failures.
[0025] The use of individual thermal interface materials, as
described above, can lead to significant challenges in creating a
stable, high-performance, reliable thermal interface that can make
and maintain effective thermal contact with both semiconductor
device surfaces and corresponding heat sink devices. Both
semiconductor device surfaces and heat sinks can have non-planar
interface surfaces, e.g., convex or concave, which can create
relatively large gaps that must be filled with thermally conductive
material to ensure efficient electronic device cooling. Many
thermal interface materials are available which yield acceptable
thermal performance, e.g., 15-20 C-mm.sup.2/W, under high thermal
load, however, none of these materials also offer adhesive
properties.
[0026] According to embodiments, various beneficial combinations of
two or more thermally conductive and adhesive materials can be
used, in combination, to create a number of adhesive-bonded thermal
interface embodiments. Such embodiments can enable an interface
having low thermal resistance without the need for external
mechanical latches and/or attachment hardware, which can be useful
on space-constrained printed circuit board (PCB) designs. In some
embodiments, adhesive materials can be used in combination with
various types of mechanical latches or attachment hardware, to
create a number of hybrid adhesive/mechanically bonded thermal
interface embodiments. Such embodiments can be useful for
effectively managing area required for mechanical latches or
attachment hardware, while providing a thermally interface solution
that can be easily reworked.
[0027] Thermal interfaces according to embodiments can have
enhanced stability, reliability and durability, relative to
single-material thermal solutions, over time and/or repeated
thermal cycles. Such interfaces may not manifest "grease pumping"
behavior, can be durable within "shock and vibration" environments,
and can be compliant and compressible under the application of a
relatively low compression force. According to embodiments, such
thermal interfaces can be used to fill a relatively wide range of
surface irregularities and/or gaps between heat-producing
electronic device and heat sink surfaces, without being subject to
adverse chemical interactions between various materials.
Embodiments can provide relatively low-cost, simple and
straightforward thermal interface implementation with minimal
surface preparation requirements, processing, and material handling
issues.
[0028] Certain embodiments relate to efficient transfer of heat
from a heat-producing electronic device, through adhesive-bonded
thermal interface structures, to a heat sink. FIG. 1 depicts an
apparatus useful for transferring heat from a heat-producing
electronic device 114, through a thermally conductive material 112,
e.g., a thermal grease, thermal paste, thermal gel or phase-change
material, contained within an inner perimeter 124, to the heat sink
116, according to embodiments. Adhesive material 104 is used to
hold the heat sink 116, thermally conductive material 112, and
heat-producing electronic device 114 together as an assembly. In
embodiments, the depicted apparatus can have low thermal
resistance, enhanced stability, reliability and durability over
time and/or repeated thermal cycles. Embodiments of the apparatus
can be useful in cooling heat-producing electronic devices such as
processor ICs, GPUs, multi-chip electronic modules and other
electronic devices requiring robust heat transfer/cooling. Such
electronic devices can be located within a wide variety of
electronic equipment including computing, server, laboratory,
medical and telecommunications devices and systems.
[0029] FIG. 1 includes two consistent views; side view 100 and
cross-section A-A view 150. View 150 is a cross-section view of the
cooling apparatus, the cooling apparatus being sectioned along line
A-A of view 100, FIG. 1. As the two views 100 and 150 depict
consistent features of the embodiments, the discussion of FIG. 1
herein is generally directed towards the various features without
reference to a particular view. Both views 100 and 150 depict the
apparatus in an assembled configuration. Embodiments of the present
disclosure can be used in conjunction with a wide variety of
heat-producing electronic devices and modules, including ICs.
[0030] A cooling apparatus designed according to embodiments can
use adhesive materials, e.g., thermal tape, to hold a heat sink
onto a heat-producing electronic device. Use of adhesive materials
can enable implementation of thermal interfaces including high
thermal conductivity, non-adhesive thermal pad material without the
need for mechanical latches or load retention hardware. Such
thermal interfaces can be useful for conserving area on
space-constrained PCB designs.
[0031] Thermal measurements of test hardware constructed and
operated according to embodiments have demonstrated and quantified
significant efficiency increase of a thermal interface between a
heat-producing electronic device and a heat sink. Measurements have
shown significant reductions in electronic device operating
temperature, decreases in interface thermal resistance and
increases in heat sink operating temperature resulting from
improved thermal interface characteristics.
[0032] Various combinations of thermal and adhesive
materials/material configurations can be used in embodiments to
implement a wide range of adhesive-bonded thermal interfaces.
According to embodiments, combinations of multiple thermally
conductive materials can be arranged in multiple layers within an
adhesive perimeter to form a thermally conductive interface between
one or more IC(s) and a heat sink. An arrangement of thermally
conductive materials, in conjunction with the use of adhesive
material(s) can provide a thermally conductive interface that makes
use of the beneficial properties, e.g., thermal conductivity, of
each of the materials while managing or eliminating the
manifestation of material properties/characteristics, e.g., grease
pumping, which are detrimental to the thermal interface.
[0033] Certain aspects of various embodiments such as the use of
low-cost materials and a relatively simple, low-cost assembly
process can be used to manage and/or limit the implementation cost
of high-efficiency thermal interfaces. A cooling apparatus designed
according to certain embodiments may be relatively simple to
assemble and rework, which can allow straightforward field
replacement electronic devices and heat sinks for complex systems
such as water-cooled systems. Such simplicity of assembly and
rework can be useful in effectively managing or reducing electronic
system field maintenance costs. Embodiments of the present
disclosure can be used to provide cost-effective cooling
apparatuses for use with heat producing electronic devices, by
using existing and proven heat sink, thermally conductive material,
TIM and electronic device technologies and materials. A cooling
apparatus designed according to embodiments may be compatible with
existing and proven electronic devices, PCBs and electronic systems
and may be a useful and cost-effective way to provide efficient
cooling for heat-producing electronic devices. A cooling apparatus
constructed according to embodiments of the present disclosure may
be installed on an existing heat-producing electronic device within
an existing electronic system.
[0034] FIG. 1 depicts a cooling apparatus that does not require
mechanical fasteners to hold the heat sink 116 onto the
heat-producing electronic device 114. Such an apparatus can be
useful in PCB designs having limited space available for cooling
devices such as heat sinks. Embodiments of the present disclosure
can be useful in providing efficient and cost-effective cooling
apparatuses for use with heat-producing electronic devices 114 by
using existing and proven heat sink, thermally conductive material,
TIM and electronic device technologies. According to embodiments,
heat-producing electronic device 114 can include one or more ICs.
Such IC(s) can be fabricated in a wide variety of IC design styles
and technologies including, but not limited to, complementary
metal-oxide semiconductor (CMOS), silicon on insulator (SOI),
analog and hybrid technologies. In embodiments, a heat-producing
electronic device 114 can also include other types of electronic
module(s) or semiconductor device(s). Although FIG. 1 depicts a
heat-producing electronic device 114 having a lid 102, according to
embodiments, heat-producing electronic devices can include both
conventional lidded or lidless package styles.
[0035] The electronic device surface 108 can include backside
surface(s) of one or more ICs, or the lid 102 that is in thermally
conductive contact with one or more heat-producing circuits, e.g.,
ICs, of the heat-producing electronic device 114. In some
embodiments, electronic device surface 108 may be substantially
planar, as depicted in FIG. 1. In some embodiments, however,
electronic device surface 108 can be warped or bowed, and can have
roughnesses or surface irregularities such as pits or bumps. Warp
or bow of electronic device surface 108 of certain packaged devices
can result from a coefficient of thermal expansion (CTE) difference
between at least one electronic device and a package or substrate
upon which the device is mounted. As an example, in some
applications, an electronic device surface 108 may have flatness
variations in a range between 75 .mu.m to 250 .mu.m across the
surface 108.
[0036] A heat sink 116 can be useful for efficiently transferring
and dissipating heat from a heat-producing electronic device 114,
in order to ensure that the device 114 can function within a
specified operating temperature range. A heat sink 116 can be
designed to be cooled by air, refrigerant, water or other cooling
fluids, and may involve the use of material phase changes, e.g.,
heat-pipe devices or technology. A heat sink can include
heat-dissipating features such as fins, fluid circulation channels
or other thermally conductive attachment features used to dissipate
heat from heat-producing electronic device 114. According to
embodiments, the term "heat sink" can also be used in reference to
devices also referred to as "heat spreaders." In embodiments, a
heat sink 116 can be fabricated from various materials that are
highly thermally conductive including, but not limited to,
aluminum, copper and various alloys such as boron nitride (BN). In
some embodiments, the heat sink surface 110 may be substantially
planar, as depicted in FIG. 1. In some embodiments, however, heat
sink surface 110 can be warped or bowed, and/or can have roughness
or surface irregularities such as pits or bumps. For example, in
some embodiments, an electronic device surface 108 may have
flatness variations in the range between 25 .mu.m and 100 .mu.m,
across the heat sink surface 110.
[0037] In some embodiments, heat sink 116 can include a protrusion
106 that extends outward from the heat sink surface 110. The
protrusion 106 can be formed as a part of heatsink surface 110
through various material forming processes, for example, casting or
milling. The protrusion 106 can be useful in creating, on the heat
sink surface 110, an area defined by inner perimeter 124 for the
placement and containment of a thermally conductive material 112.
In embodiments, protrusion 106 is located within outer perimeter
122 formed by adhesive material 104. According to embodiments, the
height of protrusion 106, i.e., the distance it extends away from
the heat sink surface 110, can be designed to be less than adhesive
material 104 thickness "T" and the thickness of thermally
conductive material 112. In embodiments, the thickness "T" also
equals the distance, in an assembled configuration, between
electronic device surface 108 and heat sink surface 110. Such a
protrusion 106 height can ensure that protrusion 106 does not
contact electronic device surface 108 when the heat sink 116 is
assembled to the heat-producing electronic device 114. Avoiding
contact of protrusion 106 with electronic device surface 108 can be
useful in preventing damage, during assembly of the heat-electronic
device 114 to the heat sink 116, and/or during a subsequent curing
process that causes shrinkage of adhesive material 104. In some
embodiments, electronic device surface 108 can be the backside of
one or more IC die, which may be cracked or damaged if pressed upon
by protrusion 106. In some embodiments, the height of the
protrusion 106 can be in a range between 40% and 90% of adhesive
material 104 thickness "T." For example, if compressed thickness
"T" of the adhesive material is 1.0 mm, then the protrusion height
can be in a range between 0.4 mm and 0.9 mm. According to
embodiments, a protrusion 106 height in this range can be useful
for containing, through surface tension, thermally conductive
material 112 within the inner perimeter 124 and adjacent to the
heat producing electronic device 114.
[0038] The boundaries formed by protrusion 106, heatsink surface
110 and electronic device surface 108, in an assembled
configuration, define an inner cavity that can be useful for
containing thermally conductive material 112. Containment of
thermally conductive material 112, e.g., a thermal grease, can be
useful in keeping the thermally conductive material 112 in contact
with both electronic device surface 108 and heat sink surface 110,
which can maintain an efficient thermal interface between the
heat-producing electronic device 114 and the heat sink 116.
Protrusion 106 can be designed to optimally and efficiently
position the thermally conductive material 112 so as to maintain
contact with particular high heat-dissipation area(s) of electronic
device 114. This contact can ensure efficient heat transfer from
particularly high heat-dissipation electronic devices such as
processors or GPUs.
[0039] Physical contact between certain types of thermally
conductive materials 112 and adhesive materials 104 can result in
chemical interactions which can degrade desirable properties of one
or both materials. Such property degradation can result in eventual
catastrophic thermal interface failures. For example the bonding
properties of adhesive material 104 can be compromised through
contact with particular types of thermally conductive materials
112, which can result in a decrease in the bond strength of
adhesive material 104. A decrease in the bond strength of adhesive
material 104 can result in the adhesive material 104 failing to
hold the heat-producing electronic device 114 to the heat sink 116,
and/or allowing leakage of thermally conductive material 112 from
the inner cavity. Protrusion 106 can be useful in providing a
physical barrier to separate thermally conductive material 112 from
adhesive material 104, and thus prevent the results of undesirable
chemical interactions, such as a decrease in adhesive material 104
bond strength.
[0040] In embodiments where a heat-producing electronic device 114
is disposed in a vertical orientation, as depicted in view 100,
containment of the thermally conductive material 112 within the
inner cavity bounded by protrusion 106 can be particularly useful.
Containment by protrusion 106 can prevent the thermally conductive
material 112 from pooling, when heated, at the bottom of the outer
perimeter 122. Such pooling can create voids over high heat
dissipation areas of electronic device surface 108, which can
dramatically reduce the efficiency and effectiveness of the thermal
interface. Protrusion 106 can also be useful in ensuring the
integrity and stability of the thermal interface over repeated
thermal cycles by mitigating "grease-pumping" or migration of
formable thermally conductive material 112.
[0041] According to embodiments, adhesive material 104 is located
between the heat-producing electronic device 114 and heat sink 116
and is affixed to both the heat sink surface 110 and to electronic
device surface 108, as depicted in view 100, FIG. 1. Adhesive
material 104 can be placed or formed in a "ring" configuration that
encloses protrusion 106 and thermally conductive material 112 as
depicted in view 150, FIG. 1. Outer perimeter 122 corresponds to an
interior edge of adhesive material 104 that encloses protrusion
106. Adhesive material exterior perimeter 126 corresponds to the
exterior edge of adhesive material 104. The boundaries formed by
the outer perimeter 122 of adhesive material 104, heatsink surface
110 and electronic device surface 108, in an assembled
configuration, define an outer cavity that can be useful for
enclosing protrusion 106 and thermally conductive material 112.
[0042] According to embodiments, adhesive material 104 can be used
in place of mechanical fasteners including, but not limited to,
latches, clips, screws and clamps, to hold together the assembly of
heat sink 116, heat-producing electronic device 114 and thermally
conductive material 112. Adhesive material 104 is useful for
holding the heat sink surface 110 in an adjacent, coplanar
orientation to the electronic device surface 108 of the
heat-producing electronic device 114. Adhesive material 104 can be
useful for creating a perimeter, i.e., outer perimeter 122, having
a thickness "T" above the surface it is applied to, e.g., heat sink
surface 110. In some embodiments, outer perimeter 122 can be used
to contain a formable thermally conductive material 112.
Containment of thermally conductive material 112 can be useful in
preventing it from flowing, when heated, away from high
heat-producing regions of electronic device surface 108 and from
heat sink surface 110. Outer perimeter 122 can also be useful in
preventing "grease pumping" or migration of thermally conductive
material 112.
[0043] According to embodiments, the adhesive material 104 can be a
pressure-sensitive adhesive (PSA) having relatively robust bonding
properties. PSAs can include, but are not limited to, double-sided
adhesive tapes, adhesive material sheets, adhesive liquids, gels,
curable gels, and adhesives in aerosol formulations. In some
embodiments, adhesive material 104 can include thermally conductive
materials such as aluminum mesh. In some embodiments, adhesive
material 104 can be thermally non-conductive, and in some
embodiments adhesive material 104 can be thermally conductive and
configured transfer heat between the electronic device surface 108
and the heat sink surface 110. For example, the thermal impedance
of a double-sided thermally conductive tape can be approximately
1.0.degree. C.-in.sup.2/W. According to embodiments, a thermally
conductive adhesive material 104 can be used as a supplemental
heat-transfer element, in conjunction with a formable thermally
conductive material 112 and/or with a TIM. Adhesives used in
embodiments generally do not include curable thermal greases or
phase-change materials such as solder. In some embodiments,
adhesive material 104 can be chemically inert, i.e., non-reactive,
with respect to the formable thermally conductive material 112. A
chemically inert adhesive material 104 can be useful in preventing
undesirable chemical reactions with thermally conductive material
112, which can prevent the degradation of desirable properties of
either material. In embodiments, adhesive material 104 can have a
thickness between 0.05 mm and 1.0 mm, depending on a particular
application. For example, an aerosol adhesive can be at thin as
0.05 mm and a double-sided thermally conductive tape can have a
thickness in a range, for example, between 0.2 mm and 0.3 mm. The
adhesion strength of commercially available adhesives can be in a
range, for example, between 10 psi and 30 psi.
[0044] According to embodiments, a PSA can be applied through
various process including, but not limited to, printing,
stenciling, dispensing, e.g., through a syringe or nozzle, or
through an aerosol spray, onto at least one of the electronic
device surface 108 and the heat sink surface 110. In some
embodiments, adhesive material 104 can be a PSA that requires
application of a specified pressure for a specified time duration
in order for adhesive activation to occur. Certain PSAs can require
an application pressure in a range between 5 psi and 20 psi, for
several seconds in order to properly activate adhesion. For
example, to affix certain double-sided adhesive tapes, an
application pressure of 10 psi for 20 seconds is required to its
activate adhesion. According to embodiments, application pressure
and time may be precisely timed and/or measured in order to ensure
to ensure proper PSA activation.
[0045] In some applications, during the operating life of the
heat-producing electronic device 114, a heatsink, e.g., 116,
adhesive material 104 and/or thermally conductive material 112 may
need to be replaced or reattached to a heat-producing electronic
device 114, through a rework process. According to embodiments,
certain types of adhesive material 104 can be removable, which can
allow parts of the assembly including heat sink 116 and
heat-producing electronic device 114 to be reworked, repaired or
replaced. By way of example, a double-sided thermal adhesive tape
can require a force in a range between 60 psi and 100 psi to
remove. Such a range of removal forces can depend on the
temperature of the adhesive; in some applications, elevating the
temperature of an adhesive material 104 may reduce the removal
force, and facilitate the adhesive's removal.
[0046] In some embodiments, an outline of the adhesive material 104
can define at least one vent 120, i.e., opening, formed between the
inner perimeter 124 and adhesive material exterior perimeter 126.
Vent 120 can be useful for equalizing pressures internal to and
external to adhesive material 104. Such pressures can be created
during thermal excursion cycles or possibly from outgas sing of
thermally conductive material 112. Pressure equalization through
vent 120 can prevent catastrophic thermal interface failure by
minimizing pressure changes within the outer cavity. Minimizing
pressure changes can be useful in preventing the detachment or
dislodging of the adhesive material 104 from the heat sink surface
110 and/or electronic device surface 108. In embodiments where the
heat-producing electronic device 114 is mounted vertically, Vent
120 can be located on a top or upper surface of adhesive material
104.
[0047] In some embodiments, affixing of the heat sink 116 to the
heat-producing electronic device 114 can include an adhesive
material curing process. Curing the adhesive material 104 can be
useful in setting or "fixing" the adhesive, which can enhance and
strengthen the bond between the heat-reducing electronic device 114
and the heat sink 116. An adhesive material curing process can also
cause shrinkage or contraction of the adhesive material 104. A
curing process can include maintaining an adhesive at specified
temperature for a specified amount of time. The specified
temperature and time may be dependent on factors such as the
adhesive type/formulation and physical dimensions of the adhesive.
For example, in some embodiments a particular adhesive may be cured
at a temperature of 70.degree. C. for 24 hours, followed by curing
at a temperature of 22.degree. C. for 7 days. Adhesive types can
also include two-part "blended" adhesives which may not require a
curing process, or which may cure at room temperature.
[0048] Certain types of adhesive material 104 can shrink during
curing process, which can provide a tensile force "F" between the
heat sink surface 110 and the electronic device surface 108 in
addition to a tensile force provided the adhesive prior to a curing
process. Tensile force "F" can serve to pull the heat producing
electronic device 114 and the heat sink 116 towards each other,
which can result in compression of thermally conductive material
112 that reduces the thermally conductive material 112 thickness
"T," or "bond line" thickness. Reduction of the thickness "T" can
shorten the heat conduction path length through the thermally
conductive material 112. Shortening the conduction path length can
lower the thermal resistance of the thermally conductive material
112 as well as the entire thermal interface. Lowering thermal
resistances can result in increased efficiency and effectiveness of
thermal interface between thermally conductive material 112 and the
electronic device surface 108 and heat sink surface 110. In
embodiments, the time and temperature of a curing process can be
precisely controlled so that the protrusion 106 does not contact or
press on the electronic device surface 108 during or after the
curing process. The shrinking or compression of adhesive material
104 can also be used to effectively reduce the protrusion 106
height necessary to contain the thermally conductive material 112
within the inner cavity.
[0049] Thermally conductive material 112 can be useful in cooling
the heat-producing electronic device 114 by providing an efficient
thermal interface path having low thermal resistance between
electronic device surface 108 and heat sink surface 110. Such a
thermal interface path can be suitable for removing large amounts
of heat from a heat-producing electronic device 114, for example a
high power output processor or GPU. According to embodiments,
thermally conductive material 112 can be a "formable" material,
i.e., one that generally responds to compressive forces by assuming
the shape of a cavity or structure containing it. A TIM pad, in
contrast to a "formable" material, may have a certain degree of
resiliency, however, will not generally assume the shape of a
cavity or structure containing it in response to compressive forces
applied to it. Thermally conductive material 112 can be useful in
filling in heat sink surface 110 and electronic device surface 108
roughnesses, reducing air gaps, and providing increased surface
area for heat transfer and more efficient electronic device
cooling. According to embodiments, thermally conductive material
112 can be a formable, highly thermally conductive compound having
relatively low thermal resistance. For example, such compounds may
have thermal resistance in a range between 0.032.degree.
C.-cm.sup.2/W and 0.162.degree. C.-cm.sup.2/W. In embodiments,
thermally conductive materials 112 can be resilient or
non-resilient. Thermally conductive materials 112 can include, but
are not limited to, thermal greases, pastes, gels, curable gels and
binders with metal particulates. In embodiments, thermally
conductive material 112 can be applied, to heat sink surface 110 or
electronic device surface 108, by dispensing or stenciling to a
thickness of up to 1.0 mm. In embodiments, use of a thermally
conductive material 112 and adhesive material 104 which are
chemically inert with respect to one another can be useful in
preventing the degradation of useful properties of either
material.
[0050] In embodiments, the inner cavity is filled with a precisely
measured and dispensed volume of thermally conductive material 112
sufficient to fill the inner cavity. If an amount of thermally
conductive material 112 placed in the inner cavity is insufficient
to fill the inner cavity, significant portions of the heat sink
surface 110 and/or electronic device surface 108 may not be in
thermally conductive contact with the thermally conductive material
112. Such lack of contact can diminish overall thermal conductivity
and cooling capacity of the thermal interface. If an amount of
thermally conductive material 112 placed in the inner cavity is in
excess of the capacity of the inner cavity, the excess thermally
conductive material 112 may flow outwards from the cavity and break
the surface tension, which can cause a pool of thermally conductive
material 112 to form despite the protrusion 106. Such pooling can
also diminish overall thermal conductivity and cooling capacity of
the thermal interface.
[0051] Pressing the heat sink 116 and the heat-producing electronic
device 114 together with a compressive force can be useful in
spreading out the formable thermally conductive material 112 to
fill in the inner cavity containing it. Such compression can also
be useful in flattening and/or thinning the thermally conductive
material 112 bond line. Flattening the bond line can create an
efficient thermal interface between the heat-producing electronic
device 114 and the heat sink 116, and can improve heat sink and
electronic device surface thermal interface characteristics.
[0052] FIG. 2 depicts an apparatus useful for transferring heat
from a heat-producing electronic device 114, through a thermally
conductive TIM pad 212 contained within an inner perimeter 222 of
adhesive material 104, to the heat sink 116, according to
embodiments consistent with the figures. Adhesive material 104 is
used to hold the heat sink 116, TIM pad 212, and heat-producing
electronic device 114 together as an assembly. In embodiments, the
depicted apparatus can have low thermal resistance, and can be
useful in cooling heat-producing electronic devices such as
processor ICs, GPUs and multi-chip electronic modules.
[0053] FIG. 2 includes two consistent views; side view 200 and
cross-section B-B view 250. View 250 is a cross-section view of the
cooling apparatus, the cooling apparatus being sectioned along line
B-B of view 200, FIG. 2. As the two views 200 and 250 depict
consistent features of the embodiments, the discussion of FIG. 2
herein is generally directed towards the various features without
reference to a particular view. Both views 200 and 250 depict the
apparatus in an assembled configuration.
[0054] FIG. 2 depicts a cooling apparatus that does not require
mechanical fasteners to hold the heat sink 116 onto the
heat-producing electronic device 114. Such an apparatus can be
useful in PCB designs having limited space available for cooling
devices such as heat sinks. According to embodiments, adhesive
material 104 can be used in place of mechanical fasteners
including, but not limited to, latches, clips, screws and clamps,
to hold together the assembly of heat sink 116, heat-producing
electronic device 114 and TIM pad 212. In embodiments, adhesive
material 104 is located between the heat-producing electronic
device 114 and heat sink 116 and is affixed to both the heat sink
surface 110 and to electronic device surface 108, as depicted in
view 200, FIG. 2. Adhesive material 104 can be placed or formed in
a "ring" having a perimeter 222 corresponding to an interior edge
of adhesive material 104.
[0055] In embodiments, TIM pad 212 is located within perimeter 222,
as depicted in view 250, FIG. 2. In an assembled configuration, the
boundaries formed by the perimeter 222 of adhesive material 104,
heatsink surface 110 and electronic device surface 108 define a
cavity that can be useful for containing TIM pad 212. Adhesive
material 104 has a thickness "T" above the surface it is applied
to, e.g., heat sink surface 110. Containment of a TIM pad 212,
e.g., a carbon fiber pad, can be useful in keeping at least a
portion of one surface of the TIM pad 212 in thermally conductive
contact with electronic device surface 108, and at least a portion
of the opposing surface of the TIM pad 212 in thermally conductive
contact with heat sink surface 110. Such thermally conductive
contact allows TIM pad 212 to cool the heat-producing electronic
device 114 by providing an efficient, thermally conductive path
having low thermal resistance between the electronic device surface
108 and the heat sink surface 110. In some embodiments, an adhesive
material 104 that is thermally conductive can be used as a
supplemental heat-transfer element in conjunction with a TIM pad
212. Particular high heat-dissipation area(s) of electronic device
surface 108 can correspond to certain electronic devices having
relatively high heat dissipation, such as a processors or GPUs. In
embodiments, adhesive material 104 can be useful in optimally and
efficiently positioning the TIM pad 212 so that it remains in a
fixed position and maintains thermally conductive contact with
these high heat-dissipation area(s), which can result in efficient
heat transfer.
[0056] Adhesive material 104 can be chemically inert, i.e.,
non-reactive, with respect to TIM pad 212. A chemically inert
adhesive material 104 can be useful in preventing undesirable
chemical reactions with the TIM pad 212, which can prevent the
degradation of useful properties of either material. In some
applications, during the operating life of the heat-producing
electronic device 114, a heatsink, e.g., 116, adhesive material 104
and/or TIM pad 212 may need to be replaced or reattached to a
heat-producing electronic device 114, through a rework process.
According to embodiments, certain types of adhesive material 104
can be removable, which can allow the assembly including heat sink
116 and heat-producing electronic device 114 to be reworked,
repaired or replaced.
[0057] Certain types of adhesive material 104 can shrink during
curing process, which can provide a tensile force "F" between the
heat sink surface 110 and the electronic device surface 108 in
addition to a tensile force provided the adhesive prior to a curing
process. Tensile force "F" can serve to pull the heat producing
electronic device 114 and the heat sink 116 towards each other,
which can result in compression of TIM pad 212 that reduces the TIM
pad 212 thickness. Reduction of the thickness "T" of TIM pad 212
can shorten the heat conduction path length through the TIM pad
212, which can lower the thermal resistance of the TIM pad 212 and
the thermal resistance of the entire thermal interface. Lowering
thermal resistances can result in increased efficiency and
effectiveness of thermal interface between TIM pad 212 and the
electronic device surface 108 and heat sink surface 110.
[0058] In contrast to a "formable" thermally conductive material, a
TIM pad 212 may have a particular degree of resiliency, however a
TIM pad 212 will not generally, in response to applied compressive
forces, assume the shape of a cavity or structure containing it. A
TIM pad 212 maintaining its overall shape can be useful in
maintaining contact, over time and multiple thermal/flexing cycles,
between the TIM pad 212 and the heat sink surface 110 and the
electronic device surface 108. Unlike a formable thermally
conductive material, a TIM pad is a solid-state material, not
subject to reflow, "grease pumping" or shape changing behaviors
when heated. According to embodiments, TIM pad 212 can be a highly
thermally conductive element having relatively low thermal
resistance. For example, such TIMs may have thermal resistance in a
range between 0.010.degree. C.-cm.sup.2/W and 0.100.degree.
C.-cm.sup.2/W. Certain TIM pads can have a low thermal resistance
relative to a thermally conductive material 112, FIG. 1. According
to embodiments, TIM pad 212 can be resilient or non-resilient, and
is generally a pre-formed, thermally conductive element that is not
an intrinsic part of an electronic device and/or electronic device
package. It can be understood that a TIM pad 212 is not an adhesive
and does not exhibit adhesive properties or forces. In some
embodiments a compliant, compressible and resilient TIM pad 212 can
be useful in providing enhanced surface thermal interfaces with
heat sink surface 110 and electronic device surface 108 by at least
partially filling in roughnesses and reducing air gaps between the
surfaces. Enhanced surface thermal interfaces can enable efficient
heat transfer and electronic device cooling by creating a low
thermal resistance path between heat-producing electronic device
114 and heat sink 116.
[0059] TIM pad 212 can be fabricated from materials including, but
are not limited to, carbon fibers, metal, phase-change materials,
compressible solid graphite and composite materials. A soft metal
alloy thermal interface material (SMA-TIM) can include a
compressible and malleable metal such as indium, which can provide
uniform thermal resistance at relatively low applied stress in a
compressed interface. For example, a pressure range between 35 psi
and 100 psi can yield relatively low thermal resistances compared
to formable thermally conductive materials such as thermal greases,
pastes or gels. For example, a 0.05-0.3 mm thick SMA-TIM can have a
thermal conductivity of 0.04.degree. C.-cm.sup.2/W at an applied
pressure of 60 psi. TIM pads can have a limited gap filling range,
for example, certain TIM pads can provide 150 .mu.m (6 mils) of gap
filling compliance.
[0060] Certain types of pre-formed TIM pads 212, e.g., graphite
pads, can be relatively fragile and subject to damage during
handling and/or assembly process(s). For example, if a TIM pad 212
falls out of the cavity formed between a heat-producing electronic
device and a heat sink, it may be damaged. In embodiments, a
tacking adhesive material 218 can be particularly useful in
preventing possible damage to the TIM pad 212 by holding or tacking
a TIM pad 212 in an aligned position adjacent to the heat sink
surface 110 or electronic device surface 108 within the cavity
during an assembly process. In embodiments, small amounts of a
tacking adhesive material 218 can be applied to a surface of the
TIM, the heat sink surface 110 or electronic device surface 108
prior to placement of the TIM pad 212 within the cavity. For
example, a dot of tacking adhesive material 218 can be applied to
the center of an area for receiving a TIM pad on the heat sink
surface 110 or electronic device surface 108. Upon contact with the
opposing heat sink surface 110 and electronic device surface 108,
or upon compression of the thermal interface assembly, tacking
adhesive material 218 can spread out into a thin layer across at
least a portion of the opposing surface(s). Tacking adhesive
material 218 can have a relatively low tendency to reflow when
heated, and in embodiments may not cover the entire area close by
perimeter 222. According to embodiments, tacking adhesive material
218 can include various material types such as transient
evaporative materials, e.g., isopropyl alcohol, or thermally
conductive materials and/or adhesives such as thermal greases,
pastes or gels. Tacking adhesive material 218 can be useful in
providing a thin, "tacky," i.e., temporary, adhesive layer useful
for holding the TIM pad 212 in place for the duration of the
assembly process.
[0061] FIG. 3 depicts an apparatus useful for transferring heat
from a heat-producing electronic device 314, through a TIM pad 312
and thermally conductive material 326 contained within a perimeter
322 of adhesive material 104, to heat sink 116, according to
embodiments consistent with the figures. Adhesive material 104 is
used to hold the heat sink 116, TIM pad 312, thermally conductive
material 326 and heat-producing electronic device 314 together as
an assembly. In embodiments, the depicted apparatus can have low
thermal resistance, and can be useful in cooling heat-producing
electronic devices such as processor ICs, GPUs and multi-chip
electronic modules.
[0062] FIG. 3 includes two consistent views; side view 300 and
cross-section C-C view 350. View 350 is a cross-section view of the
cooling apparatus, the cooling apparatus being sectioned along line
C-C of view 300, FIG. 3. As the two views 300 and 350 depict
consistent features of the embodiments, the discussion of FIG. 3
herein is generally directed towards the various features without
reference to a particular view. View 300 depicts the apparatus in
an assembled configuration, while view 350 depicts the apparatus
prior to assembly.
[0063] FIG. 3 depicts a cooling apparatus that does not require
mechanical fasteners to hold the heat sink 116 onto the
heat-producing electronic device 314. Such an apparatus can be
useful in PCB designs having limited space available for cooling
devices such as heat sinks. According to embodiments, adhesive
material 104 can be used in place of mechanical fasteners
including, but not limited to, latches, clips, screws and clamps,
to hold together the assembly of heat sink 116, heat-producing
electronic device 314, thermally conductive material 326 and TIM
pad 312. Thermally conductive material 326 can be understood to be
consistent, particularly in respect to thermal and mechanical
properties, with thermally conductive material 112, FIG. 1.
Similarly, TIM pad 312 can be understood to be consistent with TIM
pad 212, FIG. 2. Thermally conductive material 326 can be
chemically inert, i.e., non-reactive, with respect to TIM pad 312
and adhesive material 104. A chemically inert adhesive material 104
can be useful in preventing undesirable chemical reactions with the
TIM pad 312, which can prevent the degradation of useful properties
of either material. In embodiments, adhesive material 104 is
located between the heat-producing electronic device 314 and heat
sink 116 and is affixed to both the heat sink surface 110 and to
electronic device surface 308, as depicted in view 300, FIG. 3.
[0064] Although a lid, e.g., 102, FIG. 1, is not depicted as part
of heat-producing electronic device 314 in FIG. 3, in some
embodiments, heat-producing electronic device 314 can include a
lid. Adhesive material 104 can be placed or formed in a "ring"
having a maximum thickness "T" above the surface it is applied to,
e.g., heat sink surface 110 and a perimeter 322 corresponding to an
interior edge of adhesive material 104.
[0065] In embodiments, TIM pad 312 and thermally conductive
material 329 are located within perimeter 322, as depicted in view
350, FIG. 3. In an assembled configuration, the boundaries formed
by the perimeter 322 of adhesive material 104, heatsink surface 110
and electronic device surface 308 define a cavity that can be
useful for containing thermally conductive material 326 and TIM pad
312. Containment of a TIM pad 312, e.g., a carbon fiber pad, can be
useful in keeping at least a portion of one surface of the TIM pad
312 in thermally conductive contact with electronic device surface
308, and at least a portion of the opposing surface of the TIM pad
312 in thermally conductive contact with heat sink surface 110.
Such thermally conductive contact allows TIM pad 312 in conjunction
with thermally conductive material 326 to cool the heat-producing
electronic device 314 by providing an efficient, thermally
conductive path having low thermal resistance between the
electronic device surface 308 and the heat sink surface 110.
Particular high heat-dissipation area(s) of electronic device
surface 308 can correspond to certain electronic devices having
relatively high heat dissipation, such as a processors or GPUs. In
some embodiments, these areas can correspond to contact region 330,
view 300. In embodiments, thermally conductive material 326 and
adhesive material 104 can be useful in optimally and efficiently
positioning the TIM pad 312 so that it remains in a fixed position
and maintains thermally conductive contact with these high
heat-dissipation area(s), which can result in efficient heat
transfer. In some embodiments, an adhesive material 104 that is
thermally conductive can be used as a supplemental heat-transfer
element in conjunction with a TIM pad 312.
[0066] According to embodiments, both the electronic device surface
308 and the heat sink surface 110 can independently deviate from a
completely planar surface profile. Each of the surfaces 110 and 308
can include any combination of convex, concave, warped, bowed,
rippled, rough, pitted and bumped surface characteristics. For
example, electronic device surface 308 can have overall flatness
deviations from a completely planar surface in a range between 75
.mu.m and 250 .mu.m across the surface 308 of the electronic
device. Similarly, a heat sink surface 110 can have overall
flatness deviations in a range between 25 .mu.m and 100 .mu.m
across surface 110 of the heat sink. View 300 depicts electronic
device surface 308 as having a convex surface profile. Flatness
deviation such as warp or bow, in some embodiments, can result from
a CTE difference between at least one electronic device and the
substrate/package upon which the device is mounted. In this
discussion, it is understood that the "electronic device" and the
"substrate/package" referred to above are both elements of the
heat-producing electronic device 314.
[0067] According to embodiments, the electronic device surface 308
can include backside surface(s) of one or more ICs, or a lid 102
that is in thermally conductive contact with one or more
heat-producing circuits, e.g., ICs, of the heat-producing
electronic device 314. In embodiments where the heat-producing
electronic device 314 includes a lid, e.g., 102, FIG. 1, such a lid
can also assume a non-planar shape, e.g., convex or concave, in
accordance with a corresponding non-planar shape of the
heat-producing electronic device 314. The above-described
deviations from a completely planar surface profile can result in
gaps, within thermal interfaces between two mating, non-planar,
surfaces, as depicted by gap regions 328, view 300. Such gaps can
be relatively narrow and formed, for example, as a result of a
protruding feature of a warped, convex heat-producing electronic
device 314 coming into contact with a more planar heat sink surface
110. If such gaps remain unfilled with thermally conductive
material, the thermal conductivity of a thermal interface between
the surfaces can be significantly degraded, relative to thermal
interfaces between more planar surfaces having a smaller gap
size.
[0068] In some embodiments a compliant, compressible and resilient
TIM pad 312 can be useful in enhancing thermal interfaces with heat
sink surface 110 and electronic device surface 308 by at least
partially filling in roughnesses and reducing air gaps between the
surfaces. The gap-filling capability of commercially available,
solid-state TIM pads having high thermal conductivity, e.g., 312,
is typically in a limited range between 25 .mu.m and approximately
125 .mu.m-150 .mu.m (=6 mils) of compliance between adjacent
thermally conductive surfaces. This thickness generally corresponds
to the contact region 330, view 300. This thickness range
corresponds to a range of application pressures suitable for
thermal interfaces that directly contact the back of an IC die. The
maximum distance between two mated, thermally conductive surfaces
can be, in some embodiments, in a range between 200 .mu.m and 250
.mu.m. Such distances can leave gaps between a significant portion
of the mating surfaces, e.g., gap regions 328, view 300, in cases
where a TIM is the only thermally conductive material positioned
between the thermally conductive surfaces.
[0069] In embodiments, thermally conductive material 326 can be
applied, e.g., dispensed or stenciled, onto an area of either the
heat sink surface 110 or the electronic device surface 308
corresponding to a perimeter of TIM pad 312, as depicted in view
350. As an example, certain thermally conductive materials 326 can
be stenciled to a thickness of up to 300 .mu.m onto a surface. View
350 depicts thermally conductive material 326 prior to an assembly
process. Thermally conductive material 326 can be applied to either
surface 110 or 308, for example, as rectangular shapes, dots, or a
contiguous line that overlap(s) the outer edge of TIM pad 312, as
depicted in view 350. According to embodiments, the TIM pad 312 at
least partially overlaps the formable thermally conductive material
326 when the heat-producing electronic device 314, TIM pad 312,
thermally conductive material 326 and heat sink 116 are assembled.
In embodiments, compressive force applied during assembly process
can cause thermally conductive material 326 to fill gap regions
328, as depicted in view 300. Filling gap regions 328 can be useful
for enhancing the overall conductivity of a thermal interface by
filling gaps having shapes or thicknesses which cannot be
effectively filled by TIM pad 312. Such a relatively thin layer of
thermally conductive material 326 can have a lower tendency to
reflow, when heated, than a thicker layer that might be used in
thermal interfaces not including a TIM pad 312.
[0070] View 300 depicts thermally conductive material 326 pressed
into and filling gap regions 328 between TIM pad 312 and heat sink
surface 110, however, in some embodiments, thermally conductive
material 326 can be used to fill similar gap regions between TIM
pad 312 and electronic device surface 308. In embodiments,
thermally conductive material 326 can be useful in preventing
possible damage to the TIM pad 312 by holding or tacking a TIM pad
312 in an aligned position within the cavity, adjacent to the heat
sink surface 110 or electronic device surface 308, for the duration
of the assembly process. Such tacking can also be useful to avoid
the need for TIM alignment pins, which can increase thermal
interface cost and complexity, and can consume critical hardware
real estate on a PCB.
[0071] The use of two thermal interface materials each with unique,
beneficial properties, e.g., thermally conductive material 326 and
TIM pad 312, in a stacked combination can provide a reliable,
stable and efficient thermal interface between a heat-producing
electronic device and a heat sink. Embodiments of the present
disclosure can provide a combination of robust TIM compression and
full "gap-filling" bond line coverage over an entire non-planar
electronic device surface, e.g., 308. Such full coverage may not be
possible using traditional thermal interface techniques.
Embodiments can also provide enhanced thermal conductivity,
compared to other thermal interface implementations, through the
use of a TIM pad in conjunction with a relatively thin layer of
thermally conductive material. According to embodiments, a
high-performance, reliable thermal interface can be created to fill
cumulative thermal interface gaps that are greater than 300 .mu.m.
If the thermal conductivity of a TIM pad, e.g., 312, is greater
than the conductivity of thermally conductive material, e.g., 326,
an assembly including a TIM pad supplemented with a relatively thin
layer of thermally conductive material can provide higher overall
thermal conductivity than an assembly including just a relatively
thick layer of thermally conductive material.
[0072] In embodiments, the use of a highly compressible,
dispensable thermally conductive material at thermal interface
perimeter locations can allow full compressibility of the TIM,
which can result in overall thermal interface performance
enhancement and reliability. A dispensable or stencil-printed
thermal interface material, e.g., thermal grease, can be applied
over relatively low power dissipation regions, e.g., those
corresponding to memory devices, of an electronic device surface.
These regions can correspond to larger thermal interface gaps than
gaps adjacent to higher power interface regions, e.g., those
corresponding to a processor or GPU ICs. Thermally conducting
gap-filling materials can be useful at thermal interface peripheral
locations and/or corners to provide mechanical damping to enhance
TIM interface integrity during shock and vibration events that can
occur during product handling or shipment.
[0073] Embodiments of the present disclosure can use the lateral
heat conduction of a TIM pad in conjunction with the conduction of
overlapping thermal interface material and TIM pad layers to assist
in heat removal from electronic device surface areas adjacent to
relatively thick thermal interface material layers. Embodiments can
provide improvements and thermal interface performance relative to
thermal interfaces that include only thermally conductive materials
or only TIM pads. Some embodiments can useful in mitigating or
eliminating, through the placement of a TIM pad in relatively thin,
high-strain bond line regions adjacent to high power electronic
devices, the phenomena of "grease pumping" and thermal gel
delamination.
[0074] In some applications, during the operating life of the
heat-producing electronic device 314, a heatsink, e.g., 116,
adhesive material 104, thermally conductive material 326 and/or TIM
pad 312 may need to be replaced or reattached to a heat-producing
electronic device 314, through a rework process. According to
embodiments, certain types of adhesive material 104 can be
removable, which can allow the assembly including heat sink 116 and
heat-producing electronic device 314 to be reworked, repaired or
replaced.
[0075] Certain types of adhesive material 104 can shrink during
curing process, which can provide a tensile force "F" between the
heat sink surface 110 and the electronic device surface 308 in
addition to a tensile force provided the adhesive prior to a curing
process. Tensile force "F" can serve to pull the heat producing
electronic device 314 and the heat sink 116 towards each other,
which can result in compression of TIM pad 312 that reduces the TIM
pad 312 thickness. The resulting compression can also be useful in
forcing thermally conductive material 326 into gap regions 328,
view 300, from area(s) where thermally conductive material 326 is
initially dispensed, 328, view 350. Reduction of the thickness "T"
of TIM pad 312 can shorten the heat conduction path length through
the TIM pad 312, which can lower the thermal resistance of the TIM
pad 312 and the thermal resistance of the entire thermal interface.
The insertion of thermally conductive material 326 into gap regions
can also be useful for lowering the thermal resistance of the
entire thermal interface. Lowering thermal resistances can result
in increased efficiency and effectiveness of thermal interface
between TIM pad 312 and the electronic device surface 308 and heat
sink surface 110.
[0076] FIG. 4 depicts an apparatus useful for transferring heat
from a heat-producing electronic device 314, through a TIM pad 412
and thermally conductive adhesive 404, to the heat sink 116,
according to embodiments consistent with the figures. In
embodiments, TIM pad 412 partially overlaps and is contained within
thermally conductive adhesive 404. Thermally conductive adhesive
404 is used to hold the heat sink 116, TIM pad 412 and
heat-producing electronic device 314 together as an assembly, as
depicted. In embodiments, the depicted apparatus can have low
thermal resistance, and can be useful in cooling heat-producing
electronic devices such as processor ICs, GPUs and multi-chip
electronic modules.
[0077] FIG. 4 includes two consistent views; side view 400 and
cross-section D-D view 450. View 450 is a cross-section view of the
cooling apparatus, the cooling apparatus being sectioned along line
D-D of view 400, FIG. 4. As the two views 400 and 450 depict
consistent features of the embodiments, the discussion of FIG. 4
herein is generally directed towards the various features without
reference to a particular view. View 400 depicts the apparatus in
an assembled configuration, while view 450 depicts the apparatus
prior to assembly.
[0078] View 450 depicts the overlapping positioning of thermally
conductive adhesive 404 and the TIM pad 412, prior to an assembly
process and the application of a compressive force. View 400
depicts the thermally conductive adhesive 404 and the TIM pad 412
in an assembled configuration, following the application of a
compressive force. View 400 depicts the results of the thermally
conductive adhesive 404 being pressed into a gap between the TIM
pad 412 and the heat sink 116.
[0079] FIG. 4 depicts a cooling apparatus that does not require
mechanical fasteners to hold the heat sink 116 onto the
heat-producing electronic device 314. Such an apparatus can be
useful in PCB designs having limited space available for cooling
devices such as heat sinks. According to embodiments, thermally
conductive adhesive 404 can be used in place of mechanical
fasteners including, but not limited to, latches, clips, screws and
clamps, to hold together the assembly of heat sink 116,
heat-producing electronic device 314 and TIM pad 412. TIM pad 412
can be understood to be consistent with TIM pad 212, FIG. 2.
Thermally conductive adhesive 404 can be understood to be in
adhesive material having thermally conductive properties. For
example, certain commercially available thermally conductive
adhesives 404 can have a thermal impedance of 0.1.degree. C.-in2/W
at a recommended bond line thickness of 0.28 mm (280 .mu.m).
[0080] Thermally conductive adhesive 404 can be chemically inert,
i.e., non-reactive, with respect to TIM pad 412. A chemically inert
thermally conductive adhesive 404 can be useful in preventing
undesirable chemical reactions with the TIM pad 412, which can
prevent the degradation of useful properties of either material. In
embodiments, thermally conductive adhesive 404 is located between
the heat-producing electronic device 314 and heat sink 116 and is
affixed to both the heat sink surface 110 and to electronic device
surface 308, as depicted in view 400, FIG. 4. Although a lid, e.g.,
102, FIG. 1, is not depicted as part of heat-producing electronic
device 314 in FIG. 4, in some embodiments, heat-producing
electronic device 314 can include a lid. Thermally conductive
adhesive 404 can be placed or formed in a "ring" having a maximum
thickness "T" above the surface it is applied to, e.g., heat sink
surface 110, and a perimeter 422 corresponding to an interior edge
of thermally conductive adhesive 404.
[0081] In embodiments, the outline of TIM pad 412 at least
partially overlaps with perimeter 422 of thermally conductive
adhesive 404, as depicted in view 450, FIG. 4. In an assembled
configuration, thermally conductive adhesive 404, heatsink surface
110 and electronic device surface 308 define a cavity that can be
useful for containing and TIM pad 412. Containment of a TIM pad
412, e.g., a carbon fiber pad, can be useful in keeping at least a
portion of one surface of the TIM pad 412 in thermally conductive
contact with electronic device surface 308, and at least a portion
of the opposing surface of the TIM pad 412 in thermally conductive
contact with heat sink surface 110.
[0082] Such thermally conductive contact allows TIM pad 412 in
conjunction with thermally conductive adhesive 404 to cool the
heat-producing electronic device 314 by providing an efficient,
thermally conductive path having low thermal resistance between the
electronic device surface 308 and the heat sink surface 110.
Particular high heat-dissipation area(s) of electronic device
surface 308 can correspond to certain electronic devices having
relatively high heat dissipation, such as a processors or GPUs. In
some embodiments, these areas can correspond to contact region 430,
view 400. In embodiments, thermally conductive adhesive 404 can be
useful in optimally and efficiently positioning the TIM pad 412 so
that it remains in a fixed position and maintains thermally
conductive contact with these high heat-dissipation area(s), which
can result in efficient heat transfer. In embodiments, a thermally
conductive adhesive 404 be used as a supplemental heat-transfer
element in conjunction with TIM pad 412.
[0083] Deviations from a completely planar heat sink or
heat-producing electronic device surface profile can result in
gaps, within thermal interfaces between two mating, non-planar,
surfaces, as depicted by gap regions 428, view 400. Such gaps can
be relatively narrow and formed, for example, as a result of a
protruding feature of a warped, convex heat-producing electronic
device coming into contact with a more planar heat sink surface. If
such gaps remain unfilled with thermally conductive material, the
thermal conductivity of a thermal interface between the surfaces
can be significantly degraded, relative to thermal interfaces
between more planar surfaces having a smaller gap size. In some
embodiments a compliant, compressible and resilient TIM pad 412 can
be useful in enhancing thermal interfaces with heat sink surface
110 and electronic device surface 308 by at least partially filling
in roughnesses and reducing air gaps between the surfaces. The
gap-filling capability of commercially available, solid-state TIM
pads having high thermal conductivity, e.g., 412, is typically in a
limited range between 25 .mu.m and approximately 125-150 .mu.m (=6
mils) of compliance between adjacent thermally conductive surfaces.
This thickness generally corresponds to the contact region 430,
view 400. This thickness range corresponds to a range of
application pressures suitable for thermal interfaces that directly
contact the back of an IC die. The maximum distance between two
mated, thermally conductive surfaces can be, in some embodiments,
in a range between 200 .mu.m and 250 .mu.m. Such distances can
leave gaps between a significant portion of the mating surfaces,
e.g., gap regions 428, view 400, in cases where a TIM is the only
thermally conductive material positioned between the thermally
conductive surfaces.
[0084] In embodiments, thermally conductive adhesive 404 can be
applied, e.g., dispensed or stenciled, onto an area of either the
heat sink surface 110 or the electronic device surface 308 that
overlaps a perimeter of TIM pad 412, as depicted in view 450. As an
example, certain thermally conductive adhesives 404 can be
stenciled to a thickness of up to 300 .mu.m onto a surface. View
450 depicts thermally conductive adhesive 404 prior to an assembly
process. Thermally conductive adhesive 404 can be applied to either
surface 110 or 308, for example, as one or more rectangular shapes,
dots, or a contiguous line that overlap(s) the outer edge of TIM
pad 412, as depicted in view 450. According to embodiments, the TIM
pad 412 at least partially overlaps the formable thermally
conductive adhesive 404 when the heat-producing electronic device
314, TIM pad 412 and heat sink 116 are assembled. In embodiments,
compressive force applied to the assembly can cause thermally
conductive adhesive 404 to fill gap regions 428, as depicted in
view 400. Filling gap regions 428 can be useful for enhancing the
overall conductivity of a thermal interface by filling gaps having
shapes or thicknesses which cannot be effectively filled by TIM pad
412. Such a relatively thin layer of thermally conductive adhesive
404 can have a lower tendency to reflow, when heated, than a
thicker layer that might be used in thermal interfaces not
including a TIM pad 412. View 400 depicts thermally conductive
adhesive 404 pressed into and filling gap regions 428 between TIM
pad 412 and heat sink surface 110, however, in some embodiments,
thermally conductive adhesive 404 can be used to fill similar gap
regions between TIM pad 412 and electronic device surface 308.
[0085] In embodiments, thermally conductive adhesive 404 can be
useful in preventing possible damage to the TIM pad 412 by holding
or tacking a TIM pad 412 in an aligned position adjacent to the
heat sink surface 110 or electronic device surface 308, for the
duration of the assembly process. Such tacking can also be useful
in avoiding the need for TIM alignment pins, which can increase
thermal interface cost and complexity, and can consume critical
hardware real estate on a PCB.
[0086] The use of two thermal interface materials each with unique,
beneficial properties, e.g., thermally conductive adhesive 404 and
TIM pad 412, in a stacked combination can provide a reliable,
stable and efficient thermal interface between a heat-producing
electronic device and a heat sink. Embodiments can also provide
enhanced thermal conductivity, compared to other thermal interface
implementations, through the use of a TIM pad in conjunction with a
relatively thin layer of thermally conductive adhesive. Thermally
conducting gap-filling adhesive materials can be useful at thermal
interface peripheral locations and/or corners to provide mechanical
damping to enhance TIM interface integrity during shock and
vibration events that can occur during product handling or
shipment.
[0087] In some applications, during the operating life of the
heat-producing electronic device 314, a heatsink, e.g., 116,
thermally conductive adhesive 404 and/or TIM pad 412 may need to be
replaced or reattached to a heat-producing electronic device 314,
through a rework process. According to embodiments, certain types
of thermally conductive adhesive 404 can be removable, which can
allow the assembly including heat sink 116 and heat-producing
electronic device 314 to be reworked, repaired or replaced.
[0088] Certain types of thermally conductive adhesive 404 can
shrink during curing process, which can provide a tensile force "F"
between the heat sink surface 110 and the electronic device surface
308 in addition to a tensile force provided the adhesive prior to a
curing process. Tensile force "F" can serve to pull the heat
producing electronic device 314 and the heat sink 116 towards each
other, which can result in compression of TIM pad 412 that reduces
the TIM pad 412 thickness. The resulting compression can also be
useful in forcing thermally conductive adhesive 404 into gap
regions 428, view 400, from area(s) where thermally conductive
adhesive 404 is initially dispensed, as depicted in view 450.
Reduction of the thickness of TIM pad 412 can shorten the heat
conduction path length through the TIM pad 412, which can lower the
thermal resistance of the TIM pad 412 and the thermal resistance of
the entire thermal interface. The insertion of thermally conductive
adhesive 404 into gap regions can also be useful for lowering the
thermal resistance of the entire thermal interface. Lowering
thermal resistances can result in increased efficiency and
effectiveness of thermal interface between TIM pad 412 and the
electronic device surface 308 and heat sink surface 110. In some
embodiments, for example, the overall thermal resistance of a
hybrid TIM and thermally conductive adhesive material 404 can be
0.2.degree. C.-in.sup.2/W, which is a significant 80% reduction
over the thermal resistance of double-sided thermally conductive
tape by itself.
[0089] FIG. 5 includes a set of six consistent cross-sectional
views 502-512 illustrating the results of process operations for
attaching a heat sink to a heat-producing electronic device,
according to embodiments consistent with the figures, particularly
FIG. 6.
[0090] Views 502-512 illustrate an example process; other views and
operations can be possible. A thermal interface structure formed by
these process operations can be consistent with the cooling
apparatuses depicted in FIG. 1-FIG. 4, and can provide an efficient
thermal path between a heat-producing electronic device and a heat
sink. The process operations depicted in FIG. 5 can be used to
assemble a cooling apparatus that does not require mechanical
fasteners to hold the heat sink 116 onto the heat-producing
electronic device 114. Such an apparatus can be useful in PCB
designs having limited space available for cooling devices such as
heat sinks.
[0091] The progression depicted in views 502-512 begins with a heat
sink 116 and a adhesive material 104, view 502, and ends with an
assembly including heat-producing electronic device 114, thermally
conductive material 112, adhesive material 104 and heat sink 116 in
view 512. Assembly operations can be completed using commercially
available materials which can be presently used for thermal
interface construction, such as thermally conductive material 112
and adhesive material 104. A thermal interface fabricated using
these process operations can be a particularly useful assembly when
incorporated within a high-performance computing device or
system.
[0092] The results of one or more process operations may be
depicted in each view. For example, a view can depict the results
of a material application process, which can include the
application of both a tacking adhesive material and a TIM pad.
Assembly operations associated with views 502-512 can include, but
are not limited to material alignment, material application,
component assembly and affixing operations. For ease of discussion,
the views 502-512 depict an adhesive material 104, a thermally
conductive material 112 and a heat-producing electronic device 114
aligned with and assembled onto a heat sink 116. However, it can be
understood that in some embodiments the adhesive material 104,
thermally conductive material 112, and heat sink 116 can be aligned
with and assembled onto heat-producing electronic device 114.
[0093] Completed structures may be generally shown in views 502-512
as having rectangular cross-sectional profiles, with surfaces
orthogonal to each other. This depiction, however, is not limiting;
structures can be of any suitable shape, size and profile, in
accordance with specific design criteria, manufacturing process
limitations and available material profiles for a given
application. For example, corners shown as having right angles can
be rounded, surfaces can have a non-orthogonal relative
orientation, and relative dimensional ratios can vary from those
depicted in the figures.
[0094] The views 502-512 can be useful in illustrating details
involved in assembling a thermal interface that has enhanced
thermal conductivity relative to other types of thermal interface
structures, while not requiring the use of external latching
hardware to hold a heat sink to a heat-producing electronic
device.
[0095] View 502 depicts a heat sink 116 and an adhesive material
104 aligned with edges of the heat sink 116. In some embodiments
heat sink 116 includes a protrusion 106 extending away from the
substantially planar heat sink surface 110 and some embodiments,
heat sink 116 has a substantially planar heat sink surface 110 that
does not include a protrusion 106. Protrusion 106 can be useful for
containing a thermally conductive material or TIM pad within a
perimeter formed by protrusion 106. According to embodiments, heat
sink 116 can include types of heat dissipation devices which can be
cooled by dissipating heat into air, refrigerant, water or other
fluids. Adhesive material 104 can include commercially available
adhesives such as double-sided adhesive tapes, adhesive material
sheets, adhesive liquids, gels, and adhesives in aerosol
formulations. According to embodiments, adhesive material 104 can
have a thickness in a range between 0.05 mm and 1.0 mm. In some
embodiments, adhesive material 104 can be thermally conductive, and
useful as a supplemental heat conduction path between the heat sink
116 and a heat-producing electronic device 114.
[0096] View 504 depicts the results of applying the adhesive
material 104 to the heat sink surface. According to embodiments,
adhesive material 104 can be a PSA that can be applied to the heat
sink surface 110 in a "ring" shape, which can be useful for
containing thermally conductive material 112. Adhesive material 104
can be applied by processes including, but not limited to printing,
stenciling, dispensing, e.g., through a syringe or nozzle, or
through an aerosol spray. In some embodiments, adhesive material
104 can be applied in a region that overlaps at least one outer
edge of a TIM pad, which can be useful in filling gaps between the
TIM pad and at least one of the heat sink surface 110 and the
electronic device surface 108. In some embodiments, adhesive
material 104 can be useful for, in a subsequent operation, holding
or tacking a TIM pad in place during the attachment of the heat
sink 116 to the heat-producing electronic device 114. Such tacking
can be useful in preventing damage to a fragile TIM pad during the
attachment.
[0097] View 506 depicts the results of applying the thermally
conductive material 112 to the heat sink surface 110. According to
embodiments, thermally conductive material 112 can be thermal
greases, pastes, gels, curable gels and binders with metal
particulates. In some embodiments, a TIM pad, which can include
materials such as indium, silver, carbon fiber or various silicone
formulations, can be applied either alone or in combination with
thermally conductive material 112. In some embodiments, a tacking
adhesive material such as transient evaporative materials, e.g.,
isopropyl alcohol, or thermally conductive materials and/or
adhesives such as thermal greases, pastes or gels, can be applied
before applying the TIM pad, in order to hold the TIM pad in place
during the assembly process. Application of thermally conductive
material 112 and/or a TIM pad can be useful in filling gaps between
the heat sink 112 and the heat-producing electronic device 114,
thereby providing an enhanced thermal interface.
[0098] View 508 depicts a heat-producing electronic device 114
aligned with the heat sink 116. Alignment of heat-producing
electronic device 114 with heat sink 116 can be useful for ensuring
that thermally conductive material 112 is positioned to maintain
thermally conductive contact with particular high thermal output
areas of heat-producing electronic device 114, to provide efficient
heat transfer. In some embodiments, heat-producing electronic
device 114 can include a lid 102, in thermally conductive contact
with heat-producing elements, such as ICs, within heat-producing
electronic device 114. In some embodiments, heat-producing
electronic device 114 may not include a lid 102; in such
embodiments electronic device surface 108 may include the backside
of one or more IC die.
[0099] View 510 depicts the results of assembling the
heat-producing electronic device 114 to the heat sink 116.
According to embodiments, electronic device surface 108 of
heat-producing electronic device 114 is brought into contact with a
surface of adhesive material 104. As a result of this process,
thermally conductive material 112 is brought into contact with
electronic device surface 108, which is useful for establishing an
efficient thermally conductive path between the heat-producing
electric device 114 and the heat sink 116. In some embodiments,
thermally conductive material 112 can also include a TIM pad,
possibly in conjunction with thermally conductive material 112.
[0100] View 512 depicts the results of affixing the heat-producing
electronic device 114 to the heat sink 116. According to
embodiments, the heat-producing electronic device 114 may be
affixed to the heat sink 116 by applying a specified compressive
force "F1" to the assembly of the heat-producing electronic device
114 and the heat sink 116 for a specified time. Such a specified
compressive force may be useful in activating an adhesive material
104 that is pressure-sensitive. For example, certain PSAs can
require an application pressure in a range between 5 psi and 20
psi, for several seconds in order to properly activate
adhesion.
[0101] FIG. 6 is a flow diagram depicting a method 600 for
attaching heat sink to a heat-producing electronic device,
according to embodiments consistent with the figures, particularly
FIG. 5. Method 600 is directed towards attaching heat sink to a
heat-producing electronic device through the use of various
combinations of thermally conductive and adhesive materials to
achieve an efficient, highly conductive thermal interface without
the use of mechanical latching or attachment hardware. Method 600
can be useful for creating, using commercially available materials,
a robust, stable and reliable thermal interface particularly
suitable for electronic devices having a high thermal output.
Method 600 describes series of process operations used to complete
the attachment of a heat sink to a heat-producing electronic
device.
[0102] Operations depicted and described in FIG. 6 generally
correspond to the set of process operations for attaching a heat
sink to a heat-producing electronic device depicted in FIG. 5 and
described in the associated text. The arrangement of operational
blocks within the flow diagram 600 of FIG. 6 is not to be construed
as limiting the order in which the individual operations may be
performed, as certain embodiments may perform the operations of
FIG. 6 in various alternative orders. For ease of discussion, the
operations of method 600 are directed towards aligning and
assembling an adhesive material, a thermally conductive material
and a heat-producing electronic device onto a heat sink. However,
it can be understood that in some embodiments the adhesive
material, thermally conductive material, and heat sink can be
aligned with and assembled onto heat-producing electronic
device.
[0103] The process 600 moves from start 602 to operation 604.
Operation 604 generally refers to aligning an adhesive material to
a heat sink. According to embodiments, aligning an adhesive
material to a heat sink can be useful for ensuring that a thermally
conductive material contained within a perimeter formed by adhesive
material maintains contact with a specified area of a
heat-producing electronic device. Such a specified area can
correspond to particularly high thermal output devices such as
processors or GPUs. In embodiments, the operation of aligning the
adhesive material with the heat sink can be performed manually or
through the use of automated/precision machinery incorporating
optical or other types of positioning sensors. Once the adhesive
material is aligned, the process moves to operation 606.
[0104] Operation 606 generally refers to applying the adhesive
material to a surface of the heat sink. According to embodiments,
the adhesive material can be useful, when applied in a "ring" shape
to the heat sink surface, for containing thermally conductive
material and/or TIM pad in a specified location. Such containment
can provide an optimized, efficient cooling path for the
heat-producing electronic device. In embodiments, the adhesive
material can be a PSA. Once the adhesive material is applied, the
process moves to operation 608.
[0105] Operation 608 generally refers to applying a thermally
conductive material to the surface that the adhesive material is
applied to. According to embodiments, thermally conductive material
112 can be applied through printing, stenciling, dispensing, e.g.,
through a syringe or nozzle. Thermally conductive material 112 can
be useful for filling gaps between the heat sink 112 and the
heat-producing electronic device 114, thereby providing an enhanced
thermal interface. Once the thermally conductive material is
applied, the process moves to operation 610.
[0106] Operation 610 generally refers to aligning the
heat-producing electronic device to the heat sink. According to
embodiments, alignment of the heat-producing electronic device with
the heat sink can be useful for ensuring that thermally conductive
material is positioned to maintain thermally conductive contact
with particular areas of the heat heat-producing electronic device,
in order to provide efficient heat transfer from the electronic
device to the heat sink.
[0107] In embodiments, the operation of aligning the heat-producing
electronic device 114 with heat sink 116 can be performed manually
or through the use of automated/precision machinery incorporating
optical or other types of positioning sensors. Once the
heat-producing electronic device is aligned to the heat sink, the
process moves to operation 612.
[0108] Operation 612 generally refers to assembling the heat sink
to the heat-producing electronic device. According to embodiments,
a portion of the surface of the heat-producing electronic device is
brought into contact with the adhesive material while another
portion of the heat-producing electronic device surface is brought
into contact with the thermally conductive material. Establishing
such contact is useful to cause adhesion between the adhesive
material and the heat-producing electronic device and to establish
an efficient, thermally conductive contact between the thermally
conductive material and the electronic device. Once the heat sink
is assembled to the heat-producing electronic device, the process
moves to operation 614.
[0109] Operation 614 generally refers to the affixing the heat sink
to the heat-producing electronic device. According to embodiments,
the heat-producing electronic device may be affixed to the heat
sink by applying a specified compressive force to the assembly of
the heat-producing electronic device and the heat sink for a
specified time. Such a specified compressive force may be useful in
activating an adhesive material that is pressure-sensitive. Both
the magnitude and time duration of the compressive force may be
monitored and controlled manually or through the use of automated
equipment. Once heat sink is affixed to the heat-producing
electronic device, the process 600 may end at block 616.
[0110] The descriptions of the various embodiments of the present
disclosure have been presented for purposes of illustration, but
are not intended to be exhaustive or limited to the embodiments
disclosed. Many modifications and variations will be apparent to
those of ordinary skill in the art without departing from the scope
and spirit of the described embodiments. The terminology used
herein was chosen to explain the principles of the embodiments, the
practical application or technical improvement over technologies
found in the marketplace, or to enable others of ordinary skill in
the art to understand the embodiments disclosed herein.
* * * * *