U.S. patent application number 13/737123 was filed with the patent office on 2013-05-16 for thermal interface material application for integrated circuit cooling.
This patent application is currently assigned to International Business Machines Corporation. The applicant listed for this patent is International Business Machines Corporation. Invention is credited to Michael Anthony Gaynes, Dong Gun Kam, Duixian Liu, Scott Kevin Reynolds.
Application Number | 20130118008 13/737123 |
Document ID | / |
Family ID | 45806543 |
Filed Date | 2013-05-16 |
United States Patent
Application |
20130118008 |
Kind Code |
A1 |
Gaynes; Michael Anthony ; et
al. |
May 16, 2013 |
THERMAL INTERFACE MATERIAL APPLICATION FOR INTEGRATED CIRCUIT
COOLING
Abstract
Techniques provide improved thermal interface material
application in an assembly associated with an integrated circuit
package. For example, an apparatus comprises an integrated circuit
module, a printed circuit board, and a heat transfer device. The
integrated circuit module is mounted on a first surface of the
printed circuit board. The printed circuit board has at least one
thermal interface material application via formed therein in
alignment with the integrated circuit module. The heat transfer
device is mounted on a second surface of the printed circuit board
and is thermally coupled to the integrated circuit module. The
second surface of the printed circuit board is opposite to the
first surface of the printed circuit board.
Inventors: |
Gaynes; Michael Anthony;
(Vestal, NY) ; Kam; Dong Gun; (White Plains,
NY) ; Liu; Duixian; (Scarsdale, NY) ;
Reynolds; Scott Kevin; (Amawalk, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
International Business Machines Corporation; |
Armonk |
NY |
US |
|
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
45806543 |
Appl. No.: |
13/737123 |
Filed: |
January 9, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12882362 |
Sep 15, 2010 |
8411444 |
|
|
13737123 |
|
|
|
|
Current U.S.
Class: |
29/836 |
Current CPC
Class: |
H05K 2201/10098
20130101; Y10T 29/49137 20150115; H01L 2924/15321 20130101; H05K
3/0061 20130101; H05K 1/183 20130101; H01L 2224/131 20130101; H01L
2924/15153 20130101; H01L 2224/16225 20130101; H01L 2224/73253
20130101; H05K 1/0206 20130101; H05K 3/30 20130101; H05K 2201/10477
20130101; Y10T 29/49128 20150115; H01L 2223/6677 20130101; H01L
2224/131 20130101; H05K 1/141 20130101; H01L 2924/014 20130101 |
Class at
Publication: |
29/836 |
International
Class: |
H05K 3/30 20060101
H05K003/30 |
Claims
1. A method, comprising: forming at least one thermal interface
material application via in a printed circuit board; mounting an
integrated circuit module on the printed circuit board, the
integrated circuit module being mounted on a first surface of the
printed circuit board in alignment with the at least one thermal
interface material application via formed therein; mounting a heat
transfer device on a second surface of the printed circuit board in
alignment with the at least one thermal interface material
application via formed therein, the second surface of the printed
circuit board being opposite to the first surface of the printed
circuit board.
2. The method of claim 1, further comprising applying a thermal
interface material through the at least one thermal interface
material application via formed in the printed circuit board prior
to mounting the heat transfer device on a second surface of the
printed circuit board.
3. The method of claim 2, wherein the thermal interface material is
applied through the at least one thermal interface material
application by injecting the thermal interface material through the
at least one thermal interface material application via.
4. The method of claim 2, wherein the thermal interface material is
applied through the at least one thermal interface material
application via formed in the printed circuit board after one or
more components are surface-mounted on the printed circuit
board.
5. The method of claim 4, wherein the one or more components are
surface-mounted on the printed circuit board via a reflow soldering
process.
6. A method, comprising: forming at least one non-plated through
via in a printed circuit board; mounting an integrated circuit
module on the printed circuit board, the integrated circuit module
being mounted on a first surface of the printed circuit board in
alignment with the at least one non-plated through via formed
therein; mounting one or more components on the printed circuit
board via a reflow soldering process; injecting a thermal interface
material through the at least one non-plated through via; and
mounting a heat transfer device on a second surface of the printed
circuit board in alignment with the at least one non-plated through
via formed therein, the second surface of the printed circuit board
being opposite to the first surface of the printed circuit board.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a Divisional of U.S. patent application
Ser. No. 12/882,362, filed on Sep. 15, 2010, the disclosure of
which is fully incorporated herein by reference.
FIELD
[0002] The field relates generally to integrated circuit package
cooling and, more particularly, to techniques for providing
improved thermal interface material application in an assembly
including an integrated circuit package.
BACKGROUND
[0003] In today's portable electronic devices, there are typically
one or more radio frequency (RF) modules that serve to provide
wireless data exchange between the device and its operating
environment. Such an RF module requires one or more antennas to
transmit/receive data signals. The RF module and antennas are
mounted in some manner on a printed circuit board (PCB).
[0004] Until recently, the one or more antennas have been designed
independently as a printed shape on the (PCB) or as an individual
component to be assembled near an RF integrated circuit (RFIC) die.
However, the assembly of the individual antenna or antennas on the
board is problematic in the context of mass production.
[0005] Recently, it has become popular to integrate the one or more
antennas into the RF module. It is understandable that the
integration of the one or more antennas into the module brings a
huge advantage in terms of cost and performance. However, cooling
becomes very challenging since cooling devices used to transfer
heat away from the RF module, such as heat sinks and heat
spreaders, should be mounted so as not to electromagnetically
interfere with the signal transmission/reception of the one or more
antennas.
[0006] To address this interference problem, cavity-down type
integrated circuit packages have been proposed. In such a package,
the antenna-embedded package has a cavity formed on its bottom
surface in which the RFIC die is mounted. This cavity-down type
integrated circuit package is mounted on a top surface of the PCB
with a heat sink or heat spreader mounted below the PCB. This way,
the heat sink or heat spreader does not electromagnetically
interfere with the signal transmission/reception of the one or more
antennas. However, there must be some type of heat transfer
mechanism/medium employed between the components to effectively
transfer heat away from the RFIC die.
SUMMARY
[0007] Techniques provide improved thermal interface material
application in an assembly including an integrated circuit
package.
[0008] For example, in a first aspect of the invention, an
apparatus comprises an integrated circuit module, a printed circuit
board, and a heat transfer device. The integrated circuit module is
mounted on a first surface of the printed circuit board. The
printed circuit board has at least one thermal interface material
application via formed therein in alignment with the integrated
circuit module. The heat transfer device is mounted on a second
surface of the printed circuit board and is thermally coupled to
the integrated circuit module. The second surface of the printed
circuit board is opposite to the first surface of the printed
circuit board.
[0009] In one embodiment, the integrated circuit module comprises
at least one radio frequency integrated circuit (RFIC) die and at
least one embedded antenna package. The at least one RFIC die and
the at least one embedded antenna package may be electrically
coupled via a flip-chip type connection or via a wire- bond type
connection. Further, the at least one embedded antenna package may
comprise a substrate and at least one antenna embedded in the
substrate. The substrate may comprise an organic material or a
ceramic material. The at least one embedded antenna package may
comprise a surface mounting feature for mounting to the first
surface of the printed circuit board, wherein the surface mounting
feature of the substrate is one of a ball grid array, a land grid
array, and a quad flat package. Still further, the integrated
circuit module may be a cavity-down type integrated circuit
package.
[0010] In a second aspect of the invention, an antenna assembly
comprises an antenna package, a printed circuit board, and a heat
transfer device. The antenna package is mounted on a first surface
of the printed circuit board. The printed circuit board has at
least one thermal interface material application via formed therein
in alignment with the antenna package. The heat transfer device is
mounted on a second surface of the printed circuit board and is
thermally coupled to the antenna package. The second surface of the
printed circuit board is opposite to the first surface of the
printed circuit board. In one embodiment, the antenna package is a
millimeter wave antenna package.
[0011] In a third aspect of the invention, a method comprises the
following steps. At least one thermal interface material
application via is formed in a printed circuit board. An integrated
circuit module is mounted on the printed circuit board. The
integrated circuit module is mounted on a first surface of the
printed circuit board in alignment with the at least one thermal
interface material application via formed therein. A heat transfer
device is mounted on a second surface of the printed circuit board
in alignment with the at least one thermal interface material
application via formed therein. The second surface of the printed
circuit board is opposite to the first surface of the printed
circuit board.
[0012] In one embodiment, the method further comprises applying a
thermal interface material through the at least one thermal
interface material application via formed in the printed circuit
board prior to mounting the heat transfer device on a second
surface of the printed circuit board. The thermal interface
material may be applied through the at least one thermal interface
material application by injecting the thermal interface material
through the at least one thermal interface material application
via. Further, the thermal interface material may be applied through
the at least one thermal interface material application via formed
in the printed circuit board after one or more components are
surface-mounted on the printed circuit board. The one or more
components may be surface-mounted on the printed circuit board via
a reflow soldering process.
[0013] In a fourth aspect of the invention, a method comprises the
following steps. At least one non-plated through via is formed in a
printed circuit board. An integrated circuit module is mounted on
the printed circuit board. The integrated circuit module is mounted
on a first surface of the printed circuit board in alignment with
the at least one non-plated through via formed therein. One or more
components are mounted on the printed circuit board via a reflow
soldering process. A thermal interface material is injected through
the at least one non-plated through via. A heat transfer device is
mounted on a second surface of the printed circuit board in
alignment with the at least one non-plated through via formed
therein. The second surface of the printed circuit board is
opposite to the first surface of the printed circuit board.
[0014] Advantageously, the above-described techniques provide for
improved application of thermal interface material in an integrated
circuit package assembly such that the thermal interface material
is not degraded or otherwise compromised by other assembly steps.
For example, illustrative embodiments of the invention provide
efficient cooling paths within an RF module between a cooling
device (heat transfer device) and an RFIC. With the inventive
fabrication and structural arrangements, the efficiency of heat
removal is greatly improved.
[0015] These and other objects, features, and advantages of the
present invention will become apparent from the following detailed
description of illustrative embodiments thereof, which is to be
read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 illustrates an example of a placement on a printed
circuit board of a heat transfer device with respect to an
integrated circuit package, in accordance with one embodiment of
the invention.
[0017] FIG. 2 illustrates a cavity-down type integrated circuit
package, in accordance with one embodiment of the invention.
[0018] FIG. 3 illustrates a printed circuit board assembly with a
cavity-down type integrated circuit package and heat transfer
device, in accordance with one embodiment of the invention.
[0019] FIGS. 4A through 4E illustrate a method of fabricating the
printed circuit board assembly of FIG. 3.
DETAILED DESCRIPTION
[0020] Principles of the present invention will be described herein
in the context of illustrative integrated circuit packages such as
a cavity-down type integrated circuit package and illustrative
integrated circuit dies such as a radio frequency integrated
circuit (RFIC) die. However, it is to be appreciated that the
principles of the present invention are not limited to any
particular package type or IC die. Rather, the principles of the
invention are directed broadly to techniques for improved thermal
interface material application in the fabrication process of a
printed circuit board assembly that includes an integrated circuit
package and a heat transfer device. While principles of the
invention are not limited to any particular package or die types,
they are well-suited for use in millimeter (mm) wave antenna
assemblies.
[0021] As will be illustratively described herein, in the context
of various illustrative embodiments, principles of the invention
provide techniques that provide efficient dissipation of heat
generated by a semiconductor die such as an RFIC die.
[0022] Recall, as mentioned above, that when one or more antennas
are integrated into an RFIC package, such as a cavity-down type
integrated circuit package, cooling becomes very challenging since
heat transfer devices used to transfer heat away from the RF
module, such as heat sinks and heat spreaders, should be mounted so
as not to electromagnetically interfere with the signal
transmission/reception of the one or more antennas.
[0023] FIG. 1 illustrates an example of a placement of components
on a printed circuit board that accomplishes a goal of eliminating
electromagnetic interference caused by the heat transfer
device.
[0024] As shown, the printed circuit board assembly 100 in FIG. 1
comprises an integrated circuit package 102, which could be an RFIC
module that has an embedded antenna array (e.g., a mmWave package),
mounted on a first (e.g., top) surface of a printed circuit board
104. The assembly 100 also comprises a heat transfer device (heat
sink or heat spreader) 106 mounted on a second (e.g., bottom)
surface of the printed circuit board 104.
[0025] With the heat transfer device 106 mounted on the side of the
printed circuit board 104 opposite to the side of the printed
circuit board to which the integrated circuit package 102 is
mounted, the embedded antenna array in the integrated circuit
package 102 is able to transmit/receive signals without
experiencing electromagnetic interference due to the heat transfer
device 106.
[0026] FIG. 2 illustrates an example of a cavity-down type
integrated circuit package, in accordance with one embodiment of
the invention. The cavity-down type integrated circuit package 200
shown in FIG. 2 is one example of an integrated circuit package 102
(FIG. 1).
[0027] As shown, the cavity-down type integrated circuit package
200 comprises an antenna array package 202 and an RFIC die 204. The
antenna array package 202 comprises a substrate 203. The substrate
203 can comprise an organic material such as, by way of example
only, liquid-crystal polymer, polytetrafluoroethylene, or an FR4
based laminate. Alternatively, the substrate 203 can comprise a
ceramic material.
[0028] An antenna (or an antenna array with more than one antenna)
206 is embedded at the top part of the substrate 203. The RFIC die
204 and a ball grid array (BGA) 212 (or any other surface mount
packages such as land grid array (LGA) and quad flat package (QFP))
are attached to the bottom side of the substrate 203.
[0029] In this embodiment, the RFIC die 204 is flip-chip mounted so
that the backside 205 of the die is exposed and available for heat
removal. A flip-chip type connection is a method for
interconnecting semiconductor devices, such as integrated circuit
dies, to external circuitry with solder bumps that are deposited
onto the chip pads. These solder bumps (210 in FIG. 2) electrically
connect with copper pads 208 of the external circuitry, in this
case, the antenna array package 202. The copper pads are
electrically connected with the one or more antennas 206. The
solder bumps 210 are typically deposited on the chip pads on the
top side 207 of the die 204 during the final die processing step.
Thus, in order to mount the RFIC die 204 to the antenna array
package 202, the die is flipped over so that it faces down, and
aligned so that its pads align with matching pads on the antenna
array package 202, and then the solder is flowed to complete the
interconnect.
[0030] This is in contrast to wire bonding, in which the chip is
mounted upright and wires are used to interconnect the chip pads to
external circuitry. Such a wire-bond type connection may
alternatively be used to connect the RFIC die 204 and the antenna
array package 202.
[0031] FIG. 3 illustrates a printed circuit board assembly with a
cavity-down type integrated circuit package and heat transfer
device, in accordance with one embodiment of the invention. The
printed circuit board assembly 300 in FIG. 3 comprises a
cavity-down type integrated circuit package 302 mounted on a top
surface of a printed circuit board 304, and a heat transfer device
(cooling device) 306 mounted on the bottom surface of the printed
circuit board 304. Note that the cavity-down type integrated
circuit package 302 corresponds to the cavity-down type integrated
circuit package 200 in FIG. 2.
[0032] As shown in FIG. 3, the printed circuit board 304 comprises
at least one thermal interface material application via 307 formed
in alignment with the integrated circuit package 302 and the heat
transfer device 306. While only one via 307 is shown in FIG. 3, it
is understood that more than one such via 307 may be formed in the
printed circuit board 304. Via 307 is preferably non-plated. The
printed circuit board 304 also has one or more plated thermal vias
308 that connect copper pads 309 with the heat transfer device 306.
These plated thermal vias 308 are also positioned in alignment with
the integrated circuit package 302 and the heat transfer device
306.
[0033] Also as shown, a thermal interface material (TIM) 305 is in
contact with the RFIC die of the integrated circuit package 302 and
the copper pads 309. As will be explained below in the fabrication
process of FIGS. 4A through 4E, the TIM 305 is applied by injecting
the TIM through the bottom of the thermal interface material
application via 307 before the heat transfer device 306 is mounted
to the bottom of the printed circuit board 304. Examples of TIM may
include, but are not limited to, silicone oil filled with aluminum
oxide, zinc oxide, or boron nitride, micronized or pulverized
silver, and phase-change materials. TIM is used as a heat transfer
medium that allows heat energy to move from the RFIC die to the
copper pads 309 and plated thermal vias 308 of the printed circuit
board 304 to the heat transfer device 306.
[0034] FIGS. 4A through 4E illustrate a method of fabricating the
printed circuit board assembly of FIG. 3.
[0035] As shown in FIG. 4A, a ball grid array 404 is attached to
the bottom of the substrate that is part of the integrated circuit
package 402 (i.e., package 302 in FIG. 3). This is referred to as
the BGA balling process.
[0036] Next, as shown in FIG. 4B, the integrated circuit package
402 is mounted on the top surface of the printed circuit board 406
(i.e., printed circuit board 306) with the thermal interface
material application via(s) 407 (i.e., thermal interface material
application via(s) 307) formed therein. The integrated circuit
package 402 is electrically connected to the printed circuit board
406 by a reflow soldering process, in this case, a BGA reflow. As
is known, reflow soldering is a process in which a solder paste,
such as an adhesive-like mixture of powdered solder and flux, is
used to temporarily attach one or more electrical components to
their contact pads, after which the entire assembly is subjected to
controlled heat (e.g., reflow oven or some other heat source). The
controlled heat melts the solder thereby permanently connecting the
joint(s).
[0037] Then, as shown in FIG. 4C, one or more components 410 are
surface-mounted to the printed circuit board 406. These components
may be other IC chips that are part of the printed circuit board.
They are typically surface-mounted using a reflow soldering process
(similar to the one described above for BGA reflow), in this case,
an SMT (surface mount technology) reflow.
[0038] In FIG. 4D, thermal interface material (TIM) 412 (i.e., TIM
305) is injected through the bottom of the thermal interface
material application via 407 using a syringe (not shown). The TIM
412 contacts the RFIC die of the integrated circuit package 402 and
provides a thermal conduit between the RFIC die and the heat
transfer device 414 (i.e., heat transfer device 306), which is then
mounted on the bottom surface of the printed circuit board 406, as
shown in FIG. 4E. The TIM 412 establishes a low-thermal-resistance
interface between the RFIC die and the heat transfer device.
[0039] In existing fabrication processes, it is known that the TIM
is applied to the RFIC die and the corresponding area of the top
surface of the printed circuit board prior to the BGA reflow and
the SMT reflow. In such cases, the TIM is exposed to solder reflow
conditions several times. We have realized that, when using such an
existing fabrication process, the TIM fails to maintain suitable
heat transfer properties after exposure to the solder reflow. That
is, the TIM becomes degraded and non-stable. As such, with existing
fabrication processes, an extensive production qualification test
(PQT) is required to confirm TIM stability before going into
production.
[0040] However, in accordance with principles of the invention as
illustrated in FIGS. 4A through 4E, the TIM is applied after the
BGA and SMT reflows, which is made possible by the formation of
non-plated application via(s) 407 in the printed circuit board 406,
thus allowing injection of the TIM after the reflow steps but
before attachment of the heat transfer device. Since the TIM can be
injected near the very end of the assembly process and need not to
be exposed to solder reflow, the time-consuming PQT processes are
eliminated.
[0041] In one embodiment, the size of BGA balls is chosen to ensure
that the combined height of the flip-chip mounted RFIC die is less
than the BGA stand-off. In another embodiment, the package
substrate has an open cavity to accommodate the RFIC die. In such a
case, the die need not be thinned. In yet another embodiment, the
printed circuit board can have a recess larger than the size of the
die. During the BGA reflow, the die would slip into the recess.
Still further, the package substrate and the board substrate can be
made of any materials including, but not limited to, FR4,
polytetrafluoroethylene, liquid-crystal polymer based laminates or
build-up organics, as well as ceramic substrates. Also, principles
of the invention can be applied to any cavity-down type packages
for any semiconductor die.
[0042] It will be appreciated and should be understood that the
exemplary embodiments of the invention described above can be
implemented in a number of different fashions. Given the teachings
of the invention provided herein, one of ordinary skill in the
related art will be able to contemplate other implementations of
the invention. Indeed, although illustrative embodiments of the
present invention have been described herein with reference to the
accompanying drawings, it is to be understood that the invention is
not limited to those precise embodiments, and that various other
changes and modifications may be made by one skilled in the art
without departing from the scope or spirit of the invention.
* * * * *