U.S. patent application number 09/942115 was filed with the patent office on 2002-06-13 for thermal transfer plate.
This patent application is currently assigned to Intel Corporation. Invention is credited to Turner, Leonard.
Application Number | 20020070444 09/942115 |
Document ID | / |
Family ID | 23806280 |
Filed Date | 2002-06-13 |
United States Patent
Application |
20020070444 |
Kind Code |
A1 |
Turner, Leonard |
June 13, 2002 |
Thermal transfer plate
Abstract
A thermal transfer plate (TTP) includes a thermally conductive
plate, at least one footpad and at least one reference protrusion.
The footpad includes a spring zone and a standoff member. In an
implementation, the reference protrusion contacts a top surface of
a substrate. In another implementation, the reference protrusion
contacts a top surface of an integrated circuit. Both
implementations permit the thickness of the gap between the
integrated circuit and the TTP to be optimized for efficient
transfer of heat from an integrated circuit.
Inventors: |
Turner, Leonard; (Sherwood,
OR) |
Correspondence
Address: |
SCOTT C. HARRIS
Fish & Richardson P.C.
Suite 500
4350 La Jolla Village Drive
San Diego
CA
92122
US
|
Assignee: |
Intel Corporation
|
Family ID: |
23806280 |
Appl. No.: |
09/942115 |
Filed: |
August 29, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09942115 |
Aug 29, 2001 |
|
|
|
09454829 |
Dec 6, 1999 |
|
|
|
Current U.S.
Class: |
257/713 ;
257/E23.101; 438/122 |
Current CPC
Class: |
H01L 2224/16 20130101;
H01L 2224/0401 20130101; H01L 2224/73253 20130101; H01L 2924/00014
20130101; H01L 2924/00014 20130101; H01L 23/36 20130101; H01L
2924/3011 20130101 |
Class at
Publication: |
257/713 ;
438/122 |
International
Class: |
H01L 021/48; H01L
021/44; H01L 021/50 |
Claims
What is claimed is:
1. A thermal transfer plate, comprising: a thermally conductive
plate having a top side and a bottom side; at least one footpad
connected to the plate and including a spring zone and a standoff
member; and at least one reference protrusion.
2. The thermal transfer plate of claim 1 further comprising a
reference protrusion positioned to contact a top surface of a
substrate.
3. The thermal transfer plate of claim 1 further comprising a die
cavity in the bottom side of the plate.
4. The thermal transfer plate of claim 3 further comprising a
reference protrusion positioned in the die cavity.
5. The thermal transfer plate of claim 1 further comprising a
thermal hardware mounting point on the footpad.
6. The thermal transfer plate of claim 1 further comprising four
footpads connected to the plate in a substantially square
arrangement.
7. The thermal transfer plate of claim 1 further comprising a
spring zone formed in the plane of the plate.
8. A method for coupling a thermal transfer plate to an integrated
circuit package, comprising: depressing plate foot pads having
spring zones to bend towards a module substrate; and inserting
standoff members of the foot pads into mounting locations in the
module substrate.
9. The method of claim 8, further comprising permanently securing
the standoff members to a module substrate.
10. The method of claim 8, further comprising aligning reference
protrusions of the plate with the integrated circuit package before
depressing the footpads.
11. The method of claim 8, further comprising aligning a die cavity
with an integrated circuit of the integrated circuit package before
depressing the foot pads.
12. The method of claim 11, further comprising depositing a thermal
conducting material on the top surface of the integrated circuit
before aligning the die cavity.
13. The method of claim 8, further comprising connecting thermal
management hardware to mounting points on the footpads.
14. An assembly, comprising: a module substrate; an array substrate
including an integrated circuit; and a thermal transfer plate
connected to the module substrate, the thermal transfer plate
including a thermally conductive plate having a top side and a
bottom side, at least one footpad that includes a spring zone and a
standoff member, and at least one reference protrusion.
15. The assembly of claim 14 further comprising a reference
protrusion of the thermal transfer plate positioned to contact a
top surface of the array substrate.
16. The assembly of claim 14 further comprising a reference
protrusion of the thermal transfer plate positioned to contact a
top surface of the integrated circuit.
17. The assembly of claim 14 further comprising a die cavity in the
bottom side of the plate.
18. The assembly of claim 14 further comprising a thermal hardware
mounting point on the footpad.
19. The assembly of claim 14 further comprising four footpads
arranged in a substantially square configuration.
20. The assembly of claim 14 wherein the spring zone is formed in
the plane of the plate.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a thermal transfer plate
(TTP) for coupling a thermal hardware element to an integrated
circuit package. In particular, the thermal transfer plate includes
protrusions that control the spacing between the integrated circuit
and the TTP.
[0002] Semiconductor chips produce heat when powered up and
operated. Consequently, a thermally conductive plate having a
surface area larger than the semiconductor chip is typically used
to transfer heat to a heat sink or another type of thermal
management hardware. FIG. 1 is a side view of a prior art
electrical assembly 10 including a semiconductor chip 2 that
generates heat, a printed circuit board (PCB) 4, a thermally
conductive plate 5, a heat sink 6, and a clamping structure 7. The
semiconductor chip 2 is thermally coupled to the thermal plate 5 by
a thin layer of conductive material 8 or thermal grease, which
minimizes the thermal impedance between the two components. The
chip 2 is connected to the substrate 4 by means of an array of
solder ball connections 9. The thermal plate 5 contains mounting
points for the heat sink 6. Screws 11 connect the plate 5 to the
circuit board 4 through fixed standoffs 12.
[0003] The gap between the conductive plate 5 and the top surface
of the semiconductor chip 2 must not be too close because the two
surfaces should be covered entirely by the thermal grease.
Non-wetted areas increase the effective thermal resistance between
the plate and the semiconductor chip in those areas. Care must also
be taken to ensure that the gap between the top surface of the
integrated circuit and the thermal plate is not too wide because
wider gaps, even when they are filled with thermal grease, degrade
thermal performance.
[0004] The electrical assembly 10 is typically incorporated into a
computer which may be subjected to external shock and vibration
loads. Such external vibrations may create a physical separation
between the thermal plate 5 and the semiconductor chip 2. Any
separation will increase the thermal impedance between the thermal
plate and the semiconductor chip and cause an increase in the
junction temperatures of the integrated circuit. In addition, any
relative movement between the thermal plate and the semiconductor
chip may "pump" the thermal grease out of the thermal interface. A
reduction in thermal grease will also increase the thermal
impedance, resulting in an increase in the junction temperatures of
the integrated circuit.
[0005] Since the thermal plate 5 mounts on fixed standoffs 12, the
stand-off height 14 must be great enough to assure that the top
surface of the integrated circuit component 2 on the substrate 4
does not bottom out against a bottom surface of the thermal plate
5. Thus, when an electrical assembly 10 is being designed, a
designer must compensate for varying tolerances. In particular,
using the printed circuit board 4 as the references, a designer
must consider the tolerances in the flatness of the PCB, the
semiconductor thickness tolerance, the collapsed solder-ball-height
tolerance, the thermally conductive plate flatness, the thermal
plate standoff-height tolerance and several other tolerance
measures.
[0006] New generation integrated circuits, such as faster CPU
semiconductor chips, generate more heat. It would thus be desirable
to modify the assembly shown in FIG. 1 to optimize and control the
gap between the semiconductor chip and the thermally conductive
plate, and to prevent separation between the thermal element and
the integrated circuit package to ensure adequate cooling of the
integrated circuit. It would also be desirable to mitigate or
eliminate substantially all of the tolerance accumulations
described above.
SUMMARY OF THE INVENTION
[0007] Presented is a thermal transfer plate for coupling thermal
hardware to a substrate that includes an integrated circuit. The
thermal transfer plate includes a thermally conductive plate and at
least one footpad. The footpad is connected to the plate by way of
a spring zone and a standoff member. The TTP includes at least one
reference protrusion. In one implementation, the reference
protrusion contacts a top surface of a substrate. In another
implementation, the TTP includes a die cavity having at least one
reference protrusion for contacting a top surface of an integrated
circuit die.
[0008] A thermal transfer plate according to the invention
substantially eliminates tolerance accumulations which plague the
design of electrical assemblies. Further, if the reference
protrusions are formed by using a precision forming-die, then the
gap between the top portion of the integrated circuit and the plate
can be reduced. Such thin gaps transfer more heat which permits use
of the thermal transfer plate with faster running, and thus hotter,
semiconductor devices. Yet further, a TTP according to the
invention prevents an inverted impact shock from separating the TTP
from the integrated circuit die.
[0009] Other advantages and features of the invention will be
apparent from the following description and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a side view of a prior art electrical
assembly.
[0011] FIG. 2A is a simplified, exploded, perspective view of an
embodiment of an electrical assembly according to the
invention.
[0012] FIG. 2B is a perspective view of the opposite side of the
thermal transfer plate depicted in FIG. 2A.
[0013] FIG. 3A is a simplified, exploded, perspective view of
another embodiment of an electrical assembly according to the
invention.
[0014] FIG. 3B is a perspective view of the opposite side of the
thermal transfer plate depicted in FIG. 3A.
DETAILED DESCRIPTION
[0015] FIG. 2A is a simplified, exploded, perspective view of an
embodiment of an Organic-Land-Grid Array (OLGA) reference
electrical assembly 20. The OLGA component package 24 is connected
to the top surface of a module substrate 22. A semiconductor device
23, such as a central processing unit (CPU), is connected to the
top surface of the OLGA substrate 24. A thermal transfer plate
(TTP) 30 may be composed of a thermally conducting material such as
copper, and includes three reference protrusions 32 which appear as
dimples on the top side of the plate. The protrusions 32 extend to
touch the OLGA substrate 24 from the bottom of the TTP (best seen
in FIG. 2B), so that the TTP is held a specific distance from the
OLGA substrate. The protrusions may be formed with a precision
forming-die so that the height of the protrusions would be
substantially uniform making any added tolerance consideration a
relatively small number. As a result, the semiconductor 23 to
thermal transfer plate 30 gap tolerance is reduced which permits
design of a thinner gap. A thinner gap in combination with thermal
grease allows for more efficient transfer of heat which permits
hotter semiconductors to operate safely.
[0016] FIG. 2B is a perspective view of the opposite side of the
TTP 30 depicted in FIG. 2A. A die cavity 31 is dimensioned to
encase the top surface of the CPU die 23 shown in FIG. 2A. The
protrusions 32 extend out from the TTP and bottom out on the top
surface of the OLGA substrate 24 when installed. The reference
protrusions 32 fix the vertical relationship of the TTP to the
semiconductor die 23. During installation, a thermally conductive
material is deposited on the top surface of the CPU die 23 for
contacting the die cavity when the TTP plate is installed.
[0017] Referring again to FIG. 2A, the TTP 30 also includes a
plurality of footpads 34 on the outside edge portion of the plate.
Each footpad includes a spring zone 36 and a standoff member 40.
The standoff members 40 are deliberately too short to reach down to
the top surface of the module substrate 22 when the TTP is placed
on top of the OLGA substrate, to assure that the reference
protrusions 32 will bottom out on the top surface of the OLGA
substrate 24. The standoff members 40 and footpads 34 are connected
to the TTP 30 via spring zones 36 which permit depression of the
footpads toward the module substrate 22 during installation. During
installation the standoff members are permanently secured through
apertures 21 in the module substrate 22.
[0018] FIG. 2A also depicts thermal mounting points 42 on two of
the footpads 34 which are available for connection to system-level
thermal management hardware (not shown), such as a heat sink or the
like. Each mounting point 42 is located on an indented portion of
the footpad in between the spring zone 36 and the standoff member
40. Thus, when such thermal hardware is mounted to the mounting
points, a "box clamp" structure is formed. The thermal hardware
becomes one member of the box clamp structure and the module
substrate 22 becomes the other member. The box-clamp presses upward
on the solder joints of the semiconductor component and downward on
the top surface of the thermally active portion of the TTP 30. The
clamping force thus generated keeps the reference protrusions 32 in
contact with the top surface of the OLGA substrate 24. This assures
that any force exerted by the thermal hardware, such as that
produced by an upside-down product drop (for example, when a
consumer drops her laptop) will be transferred to the module
substrate 22 without disturbing the position of the thermally
active portion of the TTP 30. In addition, this footpad and
reference protrusion structure compensates for tolerance variations
in the thickness of the CPU chip 23, the variations in the
solder-ball attachment process of the CPU to the OLGA substrate 24,
and for variations in bump height or die cavity depth in the TTP
30.
[0019] The OLGA referenced electrical assembly 20 of FIGS. 2A and
2B greatly reduces the tolerance of the gap thickness between the
semiconductor die and the TTP in comparison to conventional thermal
plates. Therefore, a TTP plate may be designed to provide adequate
heat dissipation for faster semiconductor chips.
[0020] FIG. 3A is a simplified, exploded, perspective view of an
implementation of a die-referenced electrical assembly 50. (Like
reference numbers are used when describing the same elements
referred to in FIG. 2A.) An OLGA component package 24 is connected
to the top surface of a module substrate 22, and a thermal transfer
plate (TTP) 52 is shown. A semiconductor device 23, such as a
central processing unit (CPU), is connected to the top surface of
the OLGA substrate.
[0021] FIG. 3B is a perspective view of the opposite side of the
TTP 52 depicted in FIG. 3A. A die cavity 53 is dimensioned to
encase the CPU die 23 and includes reference protrusions 54 that
bottom out on the top surface of the CPU die itself when installed.
The protrusions 54 fix the relationship of the TTP to the CPU die
23, and may be formed with a precision forming-die so that the
height of the protrusions would be substantially uniform. Thus, any
added tolerance would be a very small number. Consequently, the CPU
die 23 to TTP 52 gap tolerance would be reduced which permits
design of a thinner gap to optimize heat transfer of hotter
(faster) operating semiconductors. A thermally conductive material
such as thermal grease would be deposited on the top surface of the
CPU die 23 during installation, for contacting the die cavity and
the TTP plate surface.
[0022] Referring again to FIG. 3A, the TTP 52 also includes a
plurality of footpads 34 that each include a spring zone 36 and a
standoff member 40. The standoff members 40 are deliberately too
short to reach down to the top surface of the module substrate 22
when the TTP is placed on top of the OLGA substrate 24, to assure
that the protrusions 54 of the die cavity 53 will bottom out on the
top surface of the semiconductor die 23. The standoff members 40
and footpads 34 are connected to the TTP 52 via spring members 36
which permit depression of the footpads toward the module substrate
22 during installation. The standoff members are permanently
secured through apertures 21 in the module substrate 22 when
installed.
[0023] FIG. 3A also depicts thermal mounting points 42 on two of
the footpads 34 which are available for connection to system-level
thermal management hardware (not shown), such as a heat sink or the
like. Each mounting point 42 is located on an indented portion of
the footpad in between the spring zone 36 and the standoff member
40. Thus, when such thermal hardware is mounted to the mounting
points, a "box clamp" structure is formed. The hardware becomes one
member of the box clamp structure and the module substrate 22
becomes the other member. The box-clamp presses upward on the
solder joints of the semiconductor component and downward on the
top surface of the thermally active portion of the TTP 52. The
clamping force thus generated keeps the reference protrusions 54 in
contact with the top surface of the semiconductor die 23. The
structure compensates for tolerance variations in the height of the
reference protrusions 54. Thus, the die-referenced electrical
assembly 50 eliminates all of the tolerance considerations except
for reference protrusion height variations. Consequently,
substantially all of the gap tolerance considerations of
conventional thermal plate assemblies are eliminated so that a
designer can optimize the gap thickness and thus the thickness of
the thermal grease to provide adequate heat dissipation for fast
semiconductor chips.
[0024] While exemplary implementations have been described and
shown in the drawings, such implementations are merely illustrative
and are not restrictive of the broad invention. Thus, it should be
understood that various other modifications may occur to those of
ordinary skill in the art that fall within the scope of the
following claims.
* * * * *