U.S. patent application number 10/366122 was filed with the patent office on 2004-04-22 for method and apparatus for removeably coupling a heat rejection device with a heat producing device.
This patent application is currently assigned to Cooligy Inc.. Invention is credited to Goodson, Kenneth, Kenny, Thomas.
Application Number | 20040076408 10/366122 |
Document ID | / |
Family ID | 32095792 |
Filed Date | 2004-04-22 |
United States Patent
Application |
20040076408 |
Kind Code |
A1 |
Kenny, Thomas ; et
al. |
April 22, 2004 |
Method and apparatus for removeably coupling a heat rejection
device with a heat producing device
Abstract
A method and apparatus for removeably coupling a heat rejecting
device with a heat producing device, wherein a thermal interface
material having a predetermined phase change temperature is between
the heat rejecting device and the heat producing device, the method
comprising: configuring the heat rejecting device to include at
least one heating element; and energizing the at least one heating
element for a predetermined amount of time through at least one
electrical contact, wherein a current applied to the at least one
heating element heats the at least one heating element until the
thermal interface material substantially reaches the predetermined
phase change temperature. The at least one heating element is
located on an interface surface in contact with the thermal
interface material, although alternatively on an opposite surface,
or within the apparatus.
Inventors: |
Kenny, Thomas; (San Carlos,
CA) ; Goodson, Kenneth; (Belmont, CA) |
Correspondence
Address: |
HAVERSTOCK & OWENS LLP
162 NORTH WOLFE ROAD
SUNNYVALE
CA
94086
US
|
Assignee: |
Cooligy Inc.
|
Family ID: |
32095792 |
Appl. No.: |
10/366122 |
Filed: |
February 12, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60420557 |
Oct 22, 2002 |
|
|
|
Current U.S.
Class: |
392/340 ;
257/E23.089 |
Current CPC
Class: |
H01L 23/345 20130101;
H01L 2224/16225 20130101; H01L 21/4882 20130101; H01L 2924/00014
20130101; H01L 2924/00014 20130101; H01L 23/4275 20130101; H01L
2224/73253 20130101; H01L 2224/0401 20130101 |
Class at
Publication: |
392/340 |
International
Class: |
F24H 007/00 |
Claims
What is claimed is:
1. A method of removeably coupling a heat rejecting device to a
heat producing device comprising: a. configuring the heat rejecting
device to include at least one heating element; b. applying a
thermal interface material to an interface surface of the heat
producing device, a first surface of the heating rejecting device
in contact with the thermal interface material, the thermal
interface material configured to allow engagement and disengagement
of the heat rejecting device above a predetermined temperature; and
c. applying a current to the at least one heating element for a
predetermined amount of time, wherein the at least one heating
element heats the thermal interface material above the
predetermined temperature.
2. The method according to claim 1 further comprising positioning
the heat rejecting device at a predetermined location with respect
to the heat producing device.
3. The method according to claim 1 wherein the thermal interface
material undergoes a phase change between a first temperature below
the predetermined temperature and a second temperature above the
predetermined temperature.
4. The method according to claim 3 wherein engagement of the heat
rejecting device with the heat producing device further comprises
pressing the heat rejecting device and the thermal interface
material against one another until the temperature of the thermal
interface material is substantially at the first temperature.
5. The method according to claim 3 wherein disengagement of the
heat rejecting device with the heat producing device further
comprises removing the heat rejecting device and the thermal
interface material against one another when the temperature of the
thermal interface material is substantially at the second
temperature.
6. The method according to claim 1 wherein the at least one heating
element is positioned on the first surface of the heat rejecting
device.
7. The method according to claim 1 wherein the at least one heating
element is positioned on a heat rejecting device surface opposite
of the first surface of the heat rejecting device.
8. The method according to claim 1 wherein the at least one heating
element is positioned within the heat rejecting device.
9. The method according to claim 1 wherein the at least one heating
element heats the thermal interface material in predetermined zone
locations.
10. The method according to claim 1 wherein the at least one
heating element applies heat to the thermal interface material in a
substantially uniform manner.
11. The method according to claim 1 wherein the at least one
heating element applies heat to the thermal interface material by a
plurality of heat pulses, each heat pulse being of a predetermined
time duration.
12. The method according to claim 1 further comprising configuring
the heat rejecting device to include at least one electrical
contact positioned on a predetermined surface, wherein the current
is applied through the at least one electrical contact.
13. A heat rejector device configured to be removeably coupled to a
thermal interface material, the thermal interface material
configurable to engage and disengage the heat rejector device above
a predetermined temperature, the heat rejector device comprising at
least one heating element, wherein a current applied to the at
least one heating element for a predetermined amount of time
produces an adequate amount of heat in the at least one heating
element to heat the thermal interface material above the
predetermined temperature.
14. The heat rejector device according to claim 13 wherein the
thermal interface material undergoes a phase change between a first
temperature below the predetermined temperature and a second
temperature above the predetermined temperature.
15. The heat rejector device according to claim 14 wherein the
thermal interface material engages the heat rejecting device by
being pressed against the heat rejecting device until the thermal
interface material reaches to the first temperature.
16. The heat rejector device according to claim 14 wherein the
thermal interface material disengages the heat rejecting device by
removing the heat rejecting device and the thermal interface
material from one another when the thermal interface material is at
the second temperature.
17. The heat rejector device according to claim 13, wherein the at
least one heating element is configured to be in contact with the
thermal interface material.
18. The heat rejector device according to claim 13 wherein the at
least one heating element is positioned on a surface of the heat
rejector device opposite of the thermal interface material.
19. The heat rejector device according to claim 13 wherein the at
least one heating element is positioned within the heat rejector
device.
20. The heat rejector device according to claim 13 wherein the at
least one heating element heats the thermal interface material in
predetermined zone locations.
21. The heat rejector device according to claim 13 wherein the at
least one heating element applies heat to the thermal interface
material in a substantially uniform manner.
22. The heat rejector device according to claim 13 wherein the at
least one heating element applies heat to the thermal interface
material by a plurality of heat pulses, each heat pulse being of a
predetermined time duration.
23. The heat rejector device according to claim 13 further
comprising at least one electrical contact positioned on a
predetermined surface, wherein the current is applied through the
at least one electrical contact.
24. A heat rejector device coupled to an interface material,
wherein the heat rejector device is secured to the interface
material in a first phase state and configured to be removeable
from the interface material in a second phase state, the heat
rejector device comprising at least one heating element for
applying a predetermined amount of heat to the interface material
such that the interface material undergoes a phase change from the
first phase state to the second phase state in response to the
predetermined amount of heat applied thereto by the at least one
heating element.
25. The heat rejector device according to claim 24 wherein the
interface material is in the first phase state when below a
predetermined phase change temperature.
26. The heat rejector device according to claim 25 wherein the
interface material is in the second phase state when above the
predetermined phase change temperature.
27. The heat rejector device according to claim 24 wherein the
interface material undergoes the phase change between the first
phase state and the second phase state within an appropriate amount
of time.
28. The heat rejector device according to claim 24 wherein the at
least one heating element heats the interface material in
predetermined zone locations.
29. The heat rejector device according to claim 24 wherein the at
least one heating element applies heat to the interface material in
a substantially uniform manner.
30. The heat rejector device according to claim 24 wherein the at
least one heating element applies heat to the interface material by
a plurality of heat pulses, each heat pulse being of a
predetermined time duration.
31. The heat rejector device according to claim 24 wherein the at
least one heating element is configured to be in contact with the
interface material.
32. The heat rejector device according to claim 24 wherein the at
least one heating element is positioned on a surface of the heat
rejector device opposite of the interface material.
33. The heat rejector device according to claim 24 wherein the at
least one heating element is positioned within the heat rejector
device.
34. The heat rejector device according to claim 24 further
comprising at least one electrical contact positioned on a
predetermined surface, wherein the current is applied through the
at least one electrical contact.
35. An assembly for removeably coupling a heat rejecting device to
a heat producing device, wherein a thermal interface material
having a predetermined phase change temperature is applied between
the heat rejecting device and the heat producing device, the
assembly comprising: a. means for holding an interface surface of
the heat rejecting device in contact with the thermal interface
material, wherein at least one heating element configured on the
interface surface is in contact with the thermal interface
material; and b. means for energizing the at least one heating
element for a predetermined amount of time, wherein the at least
one heating element transforms the thermal interface material to
undergo a phase change the thermal interface material substantially
reaches the predetermined phase change temperature.
36. A method of removeably coupling a heat rejecting device with a
heat producing device, wherein a thermal interface material having
a predetermined phase change temperature is between the heat
rejecting device and the heat producing device, the method
comprising: a. configuring the heat rejecting device to include at
least one heating element; and b. energizing the at least one
heating element for a predetermined amount of time, wherein a
current applied to the at least one heating element heats the at
least one heating element until the thermal interface material
substantially reaches the predetermined phase change temperature.
Description
RELATED APPLICATION
[0001] This Patent Application claims priority under 35 U.S.C. 119
(e) of the co-pending U.S. Provisional Patent Application, Serial
No. 60/420,557 filed Oct. 22, 2002, and entitled "VAPOR ESCAPE
MICROCHANNEL HEAT EXCHANGER WITH SELF ATTACHMENT MEANS". The
Provisional Patent Application, Serial No. 60/420,557 filed Oct.
22, 2002, and entitled "VAPOR ESCAPE MICROCHANNEL HEAT EXCHANGER
WITH SELF ATTACHMENT MEANS" is also hereby incorporated by
reference.
FIELD OF THE INVENTION
[0002] The invention relates to a method and apparatus for
attaching and detaching two or more devices to one another in
general, and specifically, to a method and apparatus for removeably
coupling a heat rejection device to a heat producing device.
BACKGROUND OF THE INVENTION
[0003] High power integrated circuits have evolved in recent years
towards ever increasing transistor density and clock speed. The
result of this trend is a rapid increase in the power and heat
density of modern microprocessors and an emerging need for new
cooling technologies. One aspect of this problem is addressed by
the development of novel heat rejection devices or structures
including, but not limited to heat pipes, fin-arrays with fans or
microchannel liquid coolers. All of these structures are efficient
at transporting the heat to some remote location. In all of these
cases, heat is deposited in a liquid, solid or gas medium and that
medium provides transport of the heat by conduction or
convection.
[0004] A more fundamental aspect of this problem relates to the
transfer of the heat from an electronic device through a coupling
thermal interface into the heat rejection device. A schematic of
this configuration is illustrated in FIG. 1A. The thermal interface
between the heat rejection device and the heat producing electronic
device is a critical layer in this overall system. In particular,
the interface's characteristics can place severe limits on the
overall performance of the system, regardless of the heat removing
capabilities of the heat rejection device or structure. Typically,
thermal interfaces include a thin film of material that is
positioned between contacting surfaces of the heat producing device
and the heat rejection structure, whereby the heat producing device
and the heat rejection structure may or may not be made of the same
material having a same thermal expansion coefficient.
[0005] There are cases in which the heat producing device and the
heat rejection structure are made of different materials and thus
have different thermal expansion coefficients. One example is where
the heat producing device is made from Silicon and the heat
rejection device is made from Copper. In these cases where the heat
rejection structure has a different thermal expansion coefficient
than the electronic device, the thermal interface material must be
able to maintain contact and allow shear between both of the
surfaces. Thermal greases are often used in such applications, as
the grease is "liquid" and can be sheared without losing contact
with either surface. In addition, the thermal grease has a high
viscosity such that the surfaces of the heat producing device and
heat rejection device do not separate or slide laterally when the
heat producing device is operating. FIGS. 1A and 1B illustrate a
Copper heat rejection device attached to the backside of a Silicon
chip with a layer of thermal grease in between. As shown in FIG.
1B, the copper is heated and expands due to the temperature being
produced from the Silicon chip. Since Copper has a larger thermal
expansion coefficient than Silicon, the thermal grease in between
the chip and the rejection device allows the heat rejection device
to expand without exerting force on the Silicon, as shown in FIG.
1B.
[0006] In addition, it is possible to engineer a high performance
heat rejection structure that has a thermal expansion coefficient
which matches the heat producing device. Both structures having the
same thermal expansion coefficient allows thermal interface
material to be used, whereby the thermal interface material does
not shear. Examples of these thermal attaches such as thin, solid
adhesives, include, but are not limited to metal layers, eutectic,
solder and direct fusion bonding. The thermal resistance of these
thin solid layers is lower than thermal grease. In addition, the
thermal resistance for metal attaches can be significantly lower
than thermal grease.
[0007] However, use of a thin, solid adhesive between the Silicon
device and the Copper heat rejection device causes the
Copper-Silicon sandwich to curl due to the thermal expansion
coefficient mismatch between the Silicon heat producing device and
the Copper heat rejection device. This is shown in FIG. 1C. As
shown in FIG. 1C, the differential thermal expansion between the
Copper heat rejection device and the Silicon chip results in a
bimetal bending that causes some of the bumpbonds between the
Silicon chip and the circuit board to fail.
[0008] An issue with using a metal, eutectic, or fusion bond
between the Silicon heat producing device and the metal-type heat
rejection device is the high temperature needed to form the bond
between the two devices. Melting the metal or the eutectic thermal
interface requires temperatures that exceed the thermal limitations
of the electronic device or its supporting package. This is a
reason that a eutectic or solder bond is not in wide use as a
thermal interface attach between an electronic device and a heat
rejection device, despite the performance advantages of such an
interface. In addition, melting the metal thermal interface renders
the thermal interface between the heat producing device and the
heat rejecting device to be permanent and non-reworkable. Thus, use
of a metal or eutectic as a thermal attach is not currently a
preferred material in the industry for applications requiring
repeated removal and attachment of a heat rejecting device to a
heat producing device.
[0009] What is needed is a method and apparatus for easily coupling
a heat rejection device with a heat producing electronic device
having a thermal interface therebetween, whereby the thermal
interface has a very low thermal resistance. What is also needed is
a method and apparatus for enabling a heat rejection device to be
removeably coupled with a heat producing electronic device, whereby
the heat rejection device is reworkable and can be easily removed
from the electronic device using high heating temperatures without
damaging the electronic device or the packaging and surrounding
electronics.
SUMMARY OF THE INVENTION
[0010] In one aspect of the invention, a method of removeably
coupling a heat rejecting device to a heat producing device
comprising configuring at least one heating element. The method
including applying a thermal interface material between the heat
rejecting device and the heat producing device. The thermal
interface material is configured to allow engagement and
disengagement of the heat rejecting device therewith above a
predetermined temperature. The method includes applying a current
to the heating element, via at least one electrical contact, for a
predetermined amount of time, wherein the heating element heats the
thermal interface material above the predetermined temperature. The
method further comprises positioning the heat rejecting device at a
predetermined location with respect to the heat producing device.
The thermal interface material undergoes a phase change between a
first temperature below the predetermined temperature and a second
temperature above the predetermined temperature. Engagement between
the heat rejecting device with the heat producing device further
comprises pressing the heat rejecting device and the thermal
interface material against one another until the temperature of the
thermal interface material is substantially at the first
temperature. Disengagement of the heat rejecting device with the
heat producing device further comprises removing the heat rejecting
device and the thermal interface material against one another when
the temperature of the thermal interface material is substantially
at the second temperature. The at least one heating element is
located on an interface surface in contact with the thermal
interface material, although alternatively on an opposite surface,
or within the apparatus. The heating element heats the thermal
interface material in predetermined zone locations. The heating
element applies heat to the thermal interface material in a
substantially uniform manner. The heating element applies heat to
the thermal interface material by a plurality of heat pulses, each
heat pulse being of a predetermined time duration.
[0011] In another aspect of the invention, a heat rejector device
is coupled to an interface material. The heat rejector device is
secured to the interface material in a first phase state and is
configured to be removeable from the interface material in a second
phase state. The heat rejector device comprises at least one
heating element which applies a predetermined amount of heat to the
interface material such that the interface material undergoes a
phase change from the first phase state to the second phase state
in response to the predetermined amount of heat applied thereto by
the heating element. The thermal interface material undergoes a
phase change between a first temperature, which is below the
predetermined temperature, and a second temperature, which is above
the predetermined temperature. The thermal interface material
engages the heat rejecting device by being pressed against the heat
rejecting device until the thermal interface material reaches to
the first temperature. The thermal interface material disengages
the heat rejecting device by removing the heat rejecting device and
the thermal interface material from one another when the thermal
interface material is at the second temperature. The at least one
heating element is configured to be in contact with the thermal
interface material, although the at least one heating element is
alternatively positioned on a surface of the heat rejector device
opposite of the thermal interface material or within the heat
rejector device. The at least one heating element heats the thermal
interface material in predetermined zone locations, in a
substantially uniform manner or by a plurality of heat pulses,
whereby each heat pulse is of a predetermined time duration. The
heat rejector device further comprises at least one electrical
contact positioned on a predetermined surface, wherein the current
is applied through the at least one electrical contact.
[0012] In another aspect of the invention, an assembly for
removeably coupling a heat rejecting device to a heat producing
device, wherein a thermal interface material having a predetermined
phase change temperature is applied between the heat rejecting
device and the heat producing device. The assembly comprises means
for holding an interface surface of the heat rejecting device in
contact with the thermal interface material, wherein at least one
heating element configured on the interface surface is in contact
with the thermal interface material. The assembly comprises means
for energizing the heating element for a predetermined amount of
time, wherein the at least one heating element transforms the
thermal interface material to undergo a phase change the thermal
interface material substantially reaches the predetermined phase
change temperature. The interface material is in the first phase
state when it is below a predetermined phase change temperature.
The interface material is in the second phase state when it is
above the predetermined phase change temperature. The interface
material undergoes the phase change between the first phase state
and the second phase state within an appropriate amount of time.
The at least one heating element heats the interface material in
predetermined zone locations, in a substantially uniform manner,
and/or a plurality of heat pulses, each heat pulse is of a
predetermined time duration. The at least one heating element is
configured to be in contact with the interface material, positioned
on a surface of the heat rejector device opposite of the interface
material, or positioned within the heat rejector device. The heat
rejector device including at least one electrical contact
positioned on a predetermined surface, wherein the current is
applied through the at least one electrical contact.
[0013] In another aspect of the invention, a method of removeably
coupling a heat rejecting device with a heat producing device,
wherein a thermal interface material having a predetermined phase
change temperature is applied between the heat rejecting device and
the heat producing device. The method comprising: configuring the
heat rejecting device to include at least one heating element. The
method comprises energizing the heating element for a predetermined
amount of time, wherein a current applied to the heating element
heats the heating element until the surface of the thermal
interface material substantially reaches the predetermined phase
change temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1A illustrates a Copper heat rejection device attached
to the backside of a Silicon chip with a layer of thermal grease in
between.
[0015] FIG. 1B illustrates a Copper heat rejection device attached
to the backside of a Silicon chip with a layer of thermal grease in
between and expanding due to heating.
[0016] FIG. 1C illustrates a Copper heat rejection device attached
to the backside of a Silicon chip with a layer of thermal grease in
between and undergoing bi-metal bending.
[0017] FIG. 2A illustrates a general schematic of a heat rejector
device separated from a heat producing device in accordance with
the preferred embodiment of the present invention.
[0018] FIG. 2B illustrates a general schematic of a heat rejector
device coupled to a heat producing device in accordance with the
preferred embodiment of the present invention.
[0019] FIG. 3A illustrates a schematic of a preferred coupling
method in accordance with the present invention.
[0020] FIG. 3B illustrate a schematic of a preferred coupling
method in accordance with the present invention.
[0021] FIG. 4 illustrates a flow chart describing the method of
coupling the heat rejecting device with the heat producing
device.
[0022] FIG. 5 illustrates a flow chart describing the method of
removing the heat rejecting device with the heat producing
device.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0023] FIG. 2A illustrates a general schematic of a heat rejector
device separated from a heat producing device in accordance with
the preferred embodiment of the present invention. FIG. 2B
illustrates a general schematic of a heat rejector device coupled
to a heat producing device in accordance with the preferred
embodiment of the present invention.
[0024] In particular, FIG. 2A shows a heat producing device 100,
such as an electronic device that is coupled to a circuit board 99
by an array of pins or bumpbonds98. FIG. 2A also illustrates a thin
film of thermal interface 102 applied to a top surface 101 of the
electronic device 100. As shown in FIGS. 2A-2B, the heat rejecting
device 104 or heat rejector is configured to be coupled to the
electronic device 100 via the thermal interface 102. As stated
above, the heat rejector 104 is preferably a heat sink which allows
heat to transfer from the electronic device 100 through the thermal
interface 102. Alternatively, the heat rejector 104 is any other
heat exchanger. Alternatively, the heat rejector 104 is a vapor
escape heat exchanger described in co-pending U.S. patent
application Ser. No. ______ filed ______ and entitled "______"
which is hereby incorporated by reference. As shown in FIG. 2A, the
heat rejector 104 is coupled to the thermal interface 102, whereby
heat produced by the electronic device 100 is transferred by
convection and conduction through the thermal interface 102 to the
heat rejector 104.
[0025] The thermal interface 102 is preferably a phase change
material, such as solder, whereby an attach layer 103 and the
thermal interface 102 preferably undergoes a phase change from
solid to liquid when a sufficient amount of heat is applied to it.
Alternatively, the entire thermal interface 102 undergoes a phase
change from solid to liquid when a sufficient amount of heat is
applied to it. The thermal interface 102 has small thermal
resistance and allows shear without undergoing bilateral bending.
For exemplary purposes, solder is referred to in the present
description in relation to the thermal interface 102 although any
other material which has a small thermal resistance and allows the
heat rejector 104 to be easily removeable therefrom.
[0026] As shown in FIGS. 2A and 2B, the heat rejector 104
preferably includes a series of heating elements 106 in the bottom
surface 108 of the heat rejector 104. Alternatively, as shown in
FIGS. 2A and 2B, the heating element 106' is on the upper surface
112 of the heat rejector device 104, whereby heat applied from the
heating element 106' propagates through the heat rejector device
104 to the interface 108. Alternatively, as shown in FIGS. 2A and
2B, the heating element 106" is within the heat rejector device
104, whereby heat applied from the heating element 106" propagates
through the heat rejector device 104 to the interface 108.
Alternatively, the heating elements 106 are configured within, on
the top surface 112, on the bottom surface 108, or in any
combination thereof, of the heat rejection device 104.
[0027] It is preferred that the heating elements 106 are electronic
circuits having one or more resistors, such as polysilicon
resistors. Alternatively, the heating elements 106 are wire
heaters. Alternatively, the heating elements 106 utilize any other
appropriate components which produce an adequate amount of heat, as
discussed below. Although several heating elements 106 are shown in
FIGS. 2A and 2B, any number of heating elements 106 are
contemplated within the present invention.
[0028] In addition, as shown in FIGS. 2-3, the heat rejection
device 104 includes two electrical contacts or terminals 110 on one
of its surfaces which allow current to flow to the heating elements
106. These electrical contacts 110 preferably have a dimension of
approximately 100 microns, although other sized contacts 110 are
contemplated. These electrical contacts 110 allow a brief,
high-current to flow to the heating element 106, whereby the
heating element 106 generates heat which passes to the thermal
interface 102. The heating of heating element 106 sufficiently
melts or "softens" the interface material 106 without heating the
entire electronic device 100. As a result, the heat rejector device
102 is able to be coupled to the electronic device 100 without
subjecting the electronic device 100 to unacceptable temperatures
which may damage the system.
[0029] Alternatively, the electrical contacts 110 are in the bottom
surface 108 or side surfaces or a combination of surface on the
heat rejecting device 104, as shown in FIGS. 2A-2B. Although only
two electrical terminals 110 are shown in FIGS. 2 and 3, any number
of electrical contacts are alternatively present in the heat
rejection device 104. The heating elements 106 are preferably
manufactured into the surface of the heat rejector device 104 using
standard bonding technology or other semiconductor wafer
manufacturing methods which will not be discussed in detail here.
In addition, the electrical contacts 110 are manufactured on or in
the heat rejector device 104 using started deposition and
lithography techniques. Alternatively, the electrical contacts 110
are manufactured on or in the device 104 using screen printing,
solder re-flow or any other conventional process known by one
skilled in the art.
[0030] To couple the heat rejection device 104 to the thermal
interface 102 and eventually to the electronic device 100, a
current is applied to the heating element 106 through the
electrical terminals 110. The current causes the heating element
106 to heat up to a temperature which is preferably slightly higher
than the melting point or phase change temperature of the thermal
interface 106 material. Alternatively, the temperature of the
heating element 106 is substantially higher than the phase change
temperature of the thermal interface 102. Thus, the present
invention utilizes the heat rejection device 104 as a source of
heat which causes the heat rejection device 104 to form the
engagement with the interface. In addition, the characteristics of
the thermal interface 104 cause the thermal interface 104 to
undergo a reverse phase change or "harden" when it is cooled or
returns to its equilibrium state. The hardening of the thermal
interface 104 thereby secures and holds the heat rejection device
104 to the heat producing device 102.
[0031] In the preferred embodiment, the heating element 106 is
heated to a predetermined temperature for a time period of a few
microseconds to a few minutes, depending on a variety of factors.
The temperature output required from the heater element 104 depends
on, but is not limited to, the type of thermal interface material
102 used, the amount of thermal interface material between the
electronic device 100 and heat rejector 104 and the desired
strength of the engagement between the electronic device 100 and
heat rejector device 104. Additionally, the time period of heating
the thermal interface depends on, but is not limited to, the type
of thermal interface material 102 used between the electronic
device 100 and heat rejector 104; the amount of current applied to
the heater element 106; and the heat output capacity of the heater
element 106. Nonetheless, the heating element 106 is heated to the
predetermined temperature before the electronic device 100 or the
pins 99 and circuit board 98 become warm.
[0032] In the preferred embodiment, current is steadily applied to
the heating element 106 for an appropriate amount of time,
depending on several factors, some of which are discussed above, to
heat the heating element 106 to slightly above the phase change
temperature of the interface 102. Thus, the steadily increasing
temperature of the heating element 106 is sufficiently large enough
to melt the attach layer 103 of the interface 102 without allowing
the heat to spread to the underlying package and the surrounding
components on the circuit board 99. Alternatively embodiment,
current is applied to the heating element 106 via the electrical
terminals 110, whereby the heating element 106 is heat pulsed for a
very brief time, ranging from a few microseconds to a few seconds,
depending on the factors discussed above. In this embodiment, the
heat pulse from the heating element 106 is slow enough to heat the
attach layer 103 of the interface 102. However, the heat pulse is
brief enough and low-enough in total energy that the active regions
of the electronic device 100 do not exceed their thermal budget and
thereby overheat. It should be noted that the nature of the heat
rejection device 104 dissipates the heat created by the heating
elements 106. Thus, the timing of the heating pulse is set such
that the thermal interface 102 is sufficiently heated to undergo a
phase change without the electronic device 100 and heat rejector
device 104 reaching an excessively high temperature. In other
words, the temporal duration of the heating pulse is substantially
shorter than the thermal diffusion time from the thermal interface
102 to the top surface 101 of the electronic device 100, which is
approximately 1 second.
[0033] It is preferred that the heating elements 106 are all heated
to the same temperature for the same amount of time. This method
causes the interface material 102 to uniformly undergo the phase
change across the entire surface of the attach layer 103 of the
thermal interface 102. Alternatively, the heating elements 106 heat
the attach layer 103 of the interface 102 in zones, such as
quadrants. This alternative method allows the entire interface 103
to then be formed incrementally in zones. This alternative method
also allows large amount of heat to be applied to a particular zone
of the interface 102 in a single pulse, whereby the single pulse of
heat has a temperature that is far below the amount that would
overheat the electronic device 100.
[0034] The process of coupling the heat rejector device with the
electronic device will now be discussed in detail. FIGS. 3A and 3B
illustrate a schematic of a preferred coupling method in accordance
with the present invention. As shown in FIGS. 3A and 3B, a mounting
tool 201 is in electrical contact with the terminals 210 on the
lower surface 208 of the heat rejection device 204. Alternatively,
as discussed above and shown in FIGS. 2A and 2B, the electrical
terminals are positioned on the side and/or top surfaces of the
heat rejection device 204. In addition, a pair of spring members
208 are shown in FIGS. 3A and 3B, whereby the spring members allow
the mounting tool 200 to press the heat rejection device 212 to the
thermal interface 202 and the electronic device 200. Similarly, the
spring members 208 allow the mounting tool 201 to easily remove the
heat rejection device 204 from the thermal interface 202 and the
electronic device 200, as will be discussed below. It should be
noted that the mounting tool 201 shown in FIGS. 3A and 3B is only
for exemplary purposes and any different type of geometric
arrangements of the mounting tool 201 to removeably couple the heat
rejector device 204 to the electronic device 200 is
contemplated.
[0035] FIG. 4 illustrates a flow chart of the coupling method
discussed in relation to FIGS. 3A and 3B according to the preferred
embodiment of the present invention. The heat rejector device 204
itself, along with the electrical contacts 210 and heating elements
206 is manufactured using known methods, as discussed above.
Initially, in the preferred method, the electronic device 200 is
coupled to the circuit board 99, whereby the array of pins 98 hold
the electronic device 200 into the circuit board 99 (step 300).
Alternatively, the electronic device 200 is coupled to the circuit
board 99 after the thermal interface 202 is applied to the
electronic device 200 and the heat rejection device 204 is also
coupled thereto.
[0036] Following, the thermal interface 202 is preferably applied
to the top surface of the electronic device 200 (step 302).
Alternatively, the thermal interface 202 is applied to the bottom
of the electronic device 200. Alternatively, the thermal interface
202 is applied to the top surface and the bottom surfaces,
individually or in combination on the heat rejection device 204. As
stated above, the thermal interface 202 is applied to the
electronic device 200 using technologies and methods known in the
art. The thermal interface 202, preferably solder, is in a solid
state and is susceptible to phase change when heated to its phase
change temperature.
[0037] Once the electronic device 200 is prepared to engage the
heat rejector device 204, the external mounting tool 201 (FIGS. 3A
and 3B) moves the heat rejector device 204 to an predetermined
position to couple the heat rejector device 204 to the electronic
device 200 (step 304). Preferably, the appropriate position of the
heat rejector device 204 is above the electronic device 200.
Alternatively, the appropriate position of the heat rejector device
204 is adjacent or below the electronic device 200.
[0038] The mounting tool 201 utilizes a power source 220 to move
and position the heat rejector device 204 as well as engage the
heat rejector device 204 with the thermal interface 202. In
addition, the mounting tool 201 is coupled to a heating element
power source 224 which supplies a current to the heating element
206 via the electrical contacts 208. The electrical contacts 208
complete the electrical circuit to heat the heating elements 206
and thereby engage the heat rejector device 204 with the electronic
device 200. Alternatively, the electrical contacts 210 are
positioned on the top surface or adjacent surface of the heat
rejection device 204 as discussed above. The heating element power
source 220 is preferably coupled to a control circuit 222 which
activates and controls the heating element 206. In addition, the
control circuit 222 controls the amount of time that the heating
element 206 is activated as well as whether the heating element 206
heats the thermal interface 202 gradually or in brief pulses.
[0039] As shown in FIG. 4B, the electronic device 200 is coupled to
the circuit board 99 when the heat rejection device 204 is removed
therefrom. Alternatively, the electronic device 200 is first
removed from the circuit board 99 and the heat rejection device 204
is removed thereafter. the mounting tool 201 positions the heat
rejector device 204 in contact with the attach layer 203 of the
thermal interface 202 (step 306). Power is supplied from the
heating element power source 224 and controlled by the control
circuit 222, whereby current is supplied to the heating element 206
for an appropriate amount of time, depending on the factors
discussed above (step 308). The current flowing through the heating
element 206 causes the heating element 206 to produce a sufficient
amount of heat to raise the temperature of the thermal interface
202 to above its phase change temperature (step 310). The rise in
temperature causes the thermal interface 202 to undergo a phase
change from a solid to a liquid. However, the heating element 206
produces the adequate amount of heat in a brief enough period of
time such that the heat does not pass to and thereby damage the
electronic device 200, circuit board 99 or heat rejector device
204. As stated above, the heat produced by the heating element 206
may be controlled by the controller circuit 222 to be a gradual,
uniform heating. Alternatively, the heat produced by the heating
element 206 may be controlled by the controller circuit 222 to be a
brief pulses of a predetermined time duration. In addition, as
discussed above, the heating element 206 may be configured to heat
the thermal interface 202 directly or alternatively in quadrants or
zones.
[0040] The heat rejector device 204 is then pressed against the
electronic device 200 utilizing the springs 208, whereby the
heating element 206 is at least partially embedded in the thermal
interface material 202 (step 312). The thermal interface 202, after
transforming into the liquid or softened state, allows the bottom
surface of the heat rejector device 204 to be easily pressed into
contact with the thermal interface 202. After the appropriate
amount of time of heating, the control circuit 222 terminates
supply of current to the heating element 206, thereby allowing the
heating element 206 to cool (step 314). The termination of current
in effect lowers the temperature of the thermal interface 202 below
the phase change temperature. As the temperature of the thermal
interface 202 drops below its phase change temperature, the thermal
interface 202 undergoes a reverse phase change from a liquid back
to a solid, preferably within a matter of seconds (step 316). It
should be noted that the cool down time period varies depending on
the type of thermal interface 202, thickness of the thermal
interface 202 layer, as well as other factors discussed above.
Alternatively, the thermal interface 202 rapidly cooled by a fan or
other cooling device (not shown).
[0041] Once the thermal interface 202 cools back into the solid
state, the heat rejection device 204 becomes engaged with and
secured to the electronic device 200. The properties of the solid
phase thermal interface 202 securely hold the heat rejection device
204 in place and allows heat to easily transfer from the electronic
device 200 to the heat rejection device 204 due to the low thermal
resistance of the thermal interface 202. Thereafter, the tool 200
releases the heat rejector device 204, whereby the rest of the
assembly of the system proceeds (step 316).
[0042] The process of removing the heat rejector device 204 from
the electronic device 100 will now be discussed. FIG. 5 illustrates
a flow chart of the removal method discussed in relation to FIGS.
3A and 3B according to the preferred embodiment of the present
invention. To remove the heat rejector device 104 from the heat
producing device 200, the mounting tool 201 moves and positions
itself to engage the heat rejector device 204, as shown in FIG. 3B
(step 400). Once the tool 201 engages the heat rejector device 104,
the electrodes 211 on the engaging arms of the tool 201 come into
contact with the electrical terminals 210 shown on the bottom
surface of the heat rejector device 204. Power is then supplied to
the tool 201 from the power source 224, whereby current passes
through the electrodes 211 to the heating element 206 via the
electrical terminals 110 (step 402).
[0043] The current flowing through the heating element 206 causes
the heating element 206 to produce enough heat to raise the
temperature of the thermal interface 202 above the phase change
temperature (step 404). As stated above, the heat produced by the
heating element 206 may be controlled by the controller circuit 222
to be a gradual, uniform heating. Alternatively, the heat produced
by the heating element 206 may be controlled by the controller
circuit 222 to be a brief pulses of a predetermined time duration.
In addition, as discussed above, the heating element 206 may be
configured to heat the thermal interface 202 directly or
alternatively in quadrants or zones.
[0044] The rise in temperature causes the thermal interface 202 to
undergo a phase change from solid to liquid state. However, as
stated above, the heating element 206 produces enough heat in a
brief enough period of time such that the heat minimally passes or
does not pass to the electronic device 200 or heat rejector device
204. The phase change of the thermal interface 202 into the liquid
or softened state thereby releases the heat rejector device 204
from the secured engagement (step 406). The springs shown in FIGS.
3A and 3B along the mounting arms of the tool 201 in effect pull
the heat rejector device 204 from the thermal interface 202,
thereby disengaging the hear rejector device 204 from the
electronic device 200. Once the heat rejector device 204 is removed
from the electronic device 200, the heating element 206 is no
longer in contact with the thermal interface 202. Alternatively,
after the appropriate amount of time that the thermal interface 102
has become liquid, the control circuit 206 terminates supplying the
current to the heating element 106 and disengages the heat rejector
device 104 from the electronic device 100. The termination of heat
supplied to the thermal interface 102 lowers the temperature of the
thermal interface 102, whereby the thermal interface 102 undergoes
a phase change from a liquid back to a solid preferably within a
matter of seconds (step 408).
[0045] The present invention has been described in terms of
specific embodiments incorporating details to facilitate the
understanding of the principles of construction and operation of
the invention. Such reference herein to specific embodiments and
details thereof is not intended to limit the scope of the claims
appended hereto. It will be apparent to those skilled in the art
that modification s may be made in the embodiment chosen for
illustration without departing from the spirit and scope of the
invention.
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