U.S. patent application number 10/709931 was filed with the patent office on 2005-12-08 for method and structure for selective thermal paste deposition and retention on integrated circuit chip modules.
This patent application is currently assigned to INTERNATIONAL BUSINESS MACHINES CORPORATION. Invention is credited to Lee, Tim H., Lei, Chon C., Papae, Donald J., Szenher, Francis F..
Application Number | 20050269716 10/709931 |
Document ID | / |
Family ID | 35266366 |
Filed Date | 2005-12-08 |
United States Patent
Application |
20050269716 |
Kind Code |
A1 |
Lee, Tim H. ; et
al. |
December 8, 2005 |
METHOD AND STRUCTURE FOR SELECTIVE THERMAL PASTE DEPOSITION AND
RETENTION ON INTEGRATED CIRCUIT CHIP MODULES
Abstract
An integrated circuit (IC) chip module includes at least one
integrated circuit chip mounted upon a substrate, and a plurality
of passive components mounted upon the substrate. A polymer based
bib has at least one opening formed therein, the at least one
opening configured to accommodate the at least one integrated
circuit chip therein, and the bib further configured for attachment
to one or more of the plurality of passive components. A protective
cap is mounted over the at least one integrated circuit chip and
attached to the substrate, wherein the bib is configured to retain
thereon a thermally conductive paste initially applied to at least
one of the integrated circuit chip and the protective cap.
Inventors: |
Lee, Tim H.; (New Paltz,
NY) ; Lei, Chon C.; (Poughkeepsie, NY) ;
Papae, Donald J.; (Hopewell Junction, NY) ; Szenher,
Francis F.; (Fishkill, NY) |
Correspondence
Address: |
CANTOR COLBURN LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
US
|
Assignee: |
INTERNATIONAL BUSINESS MACHINES
CORPORATION
New Orchard Road
Armonk
NY
|
Family ID: |
35266366 |
Appl. No.: |
10/709931 |
Filed: |
June 7, 2004 |
Current U.S.
Class: |
257/783 ;
257/E23.104; 257/E23.105 |
Current CPC
Class: |
H01L 23/3677 20130101;
H01L 2224/73253 20130101; H01L 2224/16225 20130101; H01L 2924/15311
20130101; H01L 2924/3011 20130101; H01L 23/3675 20130101 |
Class at
Publication: |
257/783 |
International
Class: |
H01L 023/02 |
Claims
What is claimed is:
1. (canceled)
2. A structure for retaining a thermally conductive paste used in
an integrated circuit module, comprising: a polymer based bib
having an opening formed therein, said opening being configured to
accommodate an integrated circuit chip therein; and said bib
further configured for attachment to a plurality of support
structures proximate the integrated circuit chip; wherein said bib
further comprises an adhesive surface on one side thereof, and an
opposite side thereof is configured for retaining the thermally
conductive paste initially applied to the integrated circuit
chip.
3. The structure of claim 2, wherein said bib has an operating
temperature up to at least about 260.degree. C.
4. The structure of claim 2, wherein said bib is inert with respect
to a synthetic oil.
5. The structure of claim 2, wherein said bib further comprises a
polyimide film.
6. (canceled)
7. An integrated circuit (IC) chip module, comprising: at least one
integrated circuit chip mounted upon a substrate; a plurality of
passive components mounted upon said substrate; a polymer based bib
having at least one opening formed therein, said at least one
opening configured to accommodate said at least one integrated
circuit chip therein, and said bib further configured for
attachment to one or more of said plurality of passive components;
and a protective cap mounted over said at least one integrated
circuit chip and attached to said substrate; wherein said bib is
configured to retain thereon a thermally conductive paste initially
applied to at least one of said integrated circuit chip and said
protective cap; and wherein said bib further comprises an adhesive
surface on one side thereof, and an opposite side thereof is
configured for retaining said thermally conductive paste.
8. The IC chip module of claim 7, wherein said bib has an operating
temperature up to at least about 260.degree. C.
9. The IC chip module of claim 7, wherein said bib is inert with
respect to a synthetic oil.
10. The IC chip module of claim 7, wherein said bib further
comprises a polyimide film.
11. The IC chip module of claim 7, wherein said bib is attached to
decoupling capacitors located proximate corners of said at least
one integrated circuit chip.
12. (canceled)
13. A method for selective thermal paste deposition and retention
on an integrated circuit chip module, the method comprising:
positioning a polymer based bib around an integrated circuit chip
mounted to a substrate, said bib having at least one opening formed
therein to accommodate said integrated circuit chip therein;
attaching said bib to one or more of a plurality of passive
components mounted on said substrate; and applying a thermally
conductive paste to at least one of said integrated circuit chip
and a protective cap; and mounting said protective cap over said
integrated circuit chip and attaching said protective cap to said
substrate; wherein said bib is configured to retain thereon excess
portions of said thermally conductive paste displaced by said
mounting said protective cap over said integrated circuit chip; and
wherein said bib further comprises an adhesive surface on one side
thereof, and an opposite side thereof is configured for retaining
said thermally conductive paste.
14. The method of claim 13, wherein said bib has an operating
temperature up to at least about 260.degree. C.
15. The method of claim 13, wherein said bib is inert with respect
to a synthetic oil.
16. The method of claim 13, wherein said bib further comprises a
polyimide film.
17. The method of claim 13, wherein said bib is attached to
decoupling capacitors located proximate corners of said at least
one integrated circuit chip.
Description
BACKGROUND OF INVENTION
[0001] The present invention relates generally to semiconductor
device packaging, and, more particularly, to a method and structure
for selective thermal paste deposition and retention on integrated
circuit chip modules.
[0002] The removal of heat from electronic components is a problem
continuously faced by electronic packaging engineers. As electronic
components have become smaller and more densely packed on
integrated boards and chips, designers and manufacturers now are
faced with the challenge of how to dissipate the heat generated by
these components. It is well known that many electronic components,
especially semiconductor components such as transistors and
microprocessors, are more prone to failure or malfunction at high
temperatures. Thus, the ability to dissipate heat often is a
limiting factor on the performance of the component.
[0003] Electronic components within integrated circuits have been
traditionally cooled via forced or natural convective circulation
of air within the housing of the device. In this regard, cooling
fins have been provided as an integral part of the component
package or as separately attached elements thereto for increasing
the surface area of the package exposed to convectively developed
air currents. Electric fans have also been employed to increase the
volumetric flow rate of air circulated within the housing. For high
power circuits (as well as smaller, more densely packed circuits of
presently existing designs), however, simple air circulation often
has been found to be insufficient to adequately cool the circuit
components.
[0004] It is also well known that heat dissipation, beyond that
which is attainable by simple air circulation, may be effected by
the direct mounting of the electronic component to a thermal
dissipation member such as a "cold-plate" or other heat sink. The
heat sink may be a dedicated, thermally conductive metal plate, or
simply the chassis of the device. However, the thermal interface
surfaces of an electronic component and associated heat sink are
typically irregular, either on a gross or a microscopic scale. When
these interfaces surfaces are mated, pockets or void spaces are
developed there in-between in which air may become entrapped. These
pockets reduce the overall surface area contact within the
interface, which, in turn, reduces the efficiency of the heat
transfer therethrough. Moreover, as is also well known, air is a
relatively poor thermal conductor. Thus, the presence of air
pockets within the interface reduces the rate of thermal transfer
through the interface.
[0005] To improve the efficiency of the heat transfer through the
interface, a layer of a thermally conductive material typically is
interposed between a heat sink device and electronic component to
fill in any surface irregularities and eliminate/reduce air
pockets. For example, IBM's ATC 3.8 (advanced thermal compound) is
a thermal paste applied to the surface of a chip or protective
metal cap of a single chip module (SCM) or multichip module (MCM).
The amount of paste volume applied is typically 2 to 3 times the
volume of the gap between the chip surface and the pedestal of the
protective metal cap. Once the metal cap is pressed onto the top
surface of the module during a cap attachment operation, the
thermal paste fills the gaps between the chip surface and pedestal
of the metal cap for effective thermal management.
[0006] However, as a result of the cap attachment process, some
volume of the excess thermal paste is typically squeezed out from
the chip surface and deposited onto the module surfaces adjacent to
the chip. For those module configurations where there are
separately mounted passive components (e.g., capacitors and
resistors) in close proximity to the chip (and the chip is not
underfilled), the excess paste squeezed out from the attachment
process may be deposited on the passive components and underneath
the chip. Unfortunately, the presence of thermal paste upon certain
passive components can degrade the frequency response of analog as
well as digital chip modules. In particular, passive components
(such as resistors located on the module top surface or signal
lines buried in the module substrate) can carry signals in the
gigahertz range. If covered by a thermal paste, absorption of the
high-frequency signal can take place. This in turn can have a
negative effect on the module performance and cause the module not
to meet designed electrical specifications.
[0007] Accordingly, it would be desirable to be able to implement
the application of a thermal paste for integrated circuit chip
module in a manner that prevents the paste from spreading to
unwanted areas such as on passive components, substrate wiring
traces, and beneath the chip(s).
SUMMARY OF INVENTION
[0008] The foregoing discussed drawbacks and deficiencies of the
prior art are overcome or alleviated by a structure for retaining a
thermally conductive paste used in an integrated circuit module. In
an exemplary embodiment, the structure includes a polymer based bib
having an opening formed therein, the opening being configured to
accommodate an integrated circuit chip therein. The bib further is
configured for attachment to a plurality of support structures
proximate the integrated circuit chip.
[0009] In another embodiment, an integrated circuit (IC) chip
module includes at least one integrated circuit chip mounted upon a
substrate, and a plurality of passive components mounted upon the
substrate. A polymer based bib has at least one opening formed
therein, the at least one opening configured to accommodate the at
least one integrated circuit chip therein, and the bib further
configured for attachment to one or more of the plurality of
passive components. A protective cap is mounted over the at least
one integrated circuit chip and attached to the substrate, wherein
the bib is configured to retain thereon a thermally conductive
paste initially applied to at least one of the integrated circuit
chip and the protective cap.
[0010] In still another embodiment, a method for selective thermal
paste deposition and retention on an integrated circuit chip module
includes positioning a polymer based bib around an integrated
circuit chip mounted to a substrate. The bib has at least one
opening formed therein to accommodate the integrated circuit chip
therein, and is attached to one or more of a plurality of passive
components mounted on the substrate. A thermally conductive paste
is applied to at least one of the integrated circuit chip and a
protective cap. The protective cap is mounted over the integrated
circuit chip and attached to the substrate, wherein the bib is
configured to retain thereon excess portions of the thermally
conductive paste displaced by the mounting of the protective cap
over the integrated circuit chip.
BRIEF DESCRIPTION OF DRAWINGS
[0011] Referring to the exemplary drawings wherein like elements
are numbered alike in the several Figures:
[0012] FIG. 1 is a plan view of an exemplary integrated circuit
chip module, suitable for use in accordance with an embodiment of
the invention;
[0013] FIG. 2 is a cross-sectional view of the integrated circuit
chip module, illustrating a conventional application of a
protective cap with a thermally conductive paste interface;
[0014] FIG. 3 is a plan view of a protective bib having an opening
defined therein, in accordance with an embodiment of the
invention;
[0015] FIG. 4 is a cross-sectional view of the exemplary IC chip
module, utilizing the protective bib of FIG. 3;
[0016] FIG. 5 is a process flow diagram illustrating a method for
selective thermal paste deposition and retention on integrated
circuit chip module, in accordance with a further embodiment of the
invention; and
[0017] FIG. 6 is a graph illustrating a comparison of frequency
response curves between an exemplary IC chip module utilizing the
protective bib of FIG. 3 with no underfill material, and a module
utilizing both thermal paste and underfill material.
DETAILED DESCRIPTION
[0018] Referring initially to FIG. 1, there is shown a plan view of
an exemplary integrated circuit chip module 100, suitable for use
in accordance with an embodiment of the invention. The module 100
includes a substrate 102 having one or more integrated circuit (IC)
chips 104 mounted thereon. In addition, a plurality of discrete,
stand-alone electronic components are included on the substrate
including, for example, surface mounted resistors 106, decoupling
capacitors 108, and conductive microstrip traces 110. As shown in
the cross-sectional view of FIG. 2, a metallic cap 112 or lid is
attached to the surface of the substrate 102 for mechanically
protecting the chip 104, and to provide a heat transfer path from
the back of the chip 104 to the external cooling environment. In
order to enhance heat transfer, a highly thermally conductive paste
114 containing ceramic, metal and/or metal oxide particles or the
like (e.g., ATC 3.8) is applied between the back of the chip 104
and the cap 112. In a conventional application of the thermal
paste, the compression of the cap 112 causes excess paste material
to be squeezed beyond the boundaries of the chip surface and onto
the passive components, such as resistors 106 and decoupling
capacitors 108.
[0019] As indicated previously, the thermal paste 114 used to
provide a low thermal resistive path between the chip 104 and the
package lid 112 contains metal oxides. Thus, the smearing of the
thermal paste 114 from the chip 104 onto the top surface of the
substrate 102 changes the electrical characteristics of the chip
104, as well as the surface mounted passive components and the
microstrip transmission line traces on or below the top surface the
substrate 102. In a linear wideband amplifier circuit (e.g., DC to
about 7 GHz or more) this change in electrical characteristics
causes changes in gain over the desired frequency band, thereby
severely limiting the bandwidth of the device and the gain flatness
over the frequency band.
[0020] Moreover, for certain mixed signal and analog devices, it is
detrimental to the overall operation of the module to have the chip
(die) underfilled with an epoxy during the module fabrication
process. More specifically, the inherent dielectric constant of
underfill material reduces the effective bandwidth of the device
and can adversely affect input and output impedance matching.
Accordingly, unwanted underfill material (such as excess thermal
paste and/or epoxy) may change the impedance of chip top level
metal interconnects, as well as change the distributed capacitance
of top level inductor structures used as filters or for
input/output impedance matching. In other words, for certain
integrated circuit applications, it is desirable to maintain an air
gap between the chip and the substrate.
[0021] Therefore, in accordance with an embodiment of the
invention, there is disclosed a structure and method for retaining
thermal paste upon application of a protective lid to an integrated
circuit module. In this regard, a polymer based protective "bib" is
applied around the perimeter of the IC chip (or chips) on the
module and mounted over a plurality of individual surface-mounted
components such as the decoupling capacitors. In this manner, the
bib supports the excess thermal paste displaced by the contact
between the protective lid and the IC chip, thus keeping the paste
from forming over the surface mounted components and beneath the
chip to maintain desired device performance.
[0022] FIG. 3 is a plan view illustrating a protective bib 200
having an opening 202 defined therein to accommodate the dimensions
of the IC chip. The opening 202 in the bib 200 is generally sized
in accordance with x-y dimensions of the chip, accounting for an
additional tolerance (e.g., 0.001 inch) in each direction. Again,
since the exemplary embodiment illustrates a single chip module, it
will be appreciated that for multichip modules, the bib 200 would
be patterned with an appropriate number of openings to accommodate
each chip on the module. In an exemplary embodiment, the bib 200 is
formed from a thin piece of plastic film having an operating
temperature up to about 260.degree. C., that is inert with respect
to a synthetic oil, and that has an adhesive coating on a back side
thereof. Accordingly, one suitable material for the bib 200 is
Kapton.RTM., a polyimide insulating film available from DuPont.
Other types of material, however, are also contemplated.
[0023] FIG. 4 is a cross-sectional view of the IC chip module 100,
utilizing the protective bib 200 of FIG. 3. Prior to the
application of the protective bib 200, the chip 104 and other
passive components mounted on the surface of the substrate 102 are
subjected to normal joining and reflow processes. Then, the bib is
manually applied around the chip 104 by pressing the bottom
adhesive of the bib 200 against the top surface of surrounding
surface mounted components, such as the decoupling capacitors 108.
In an exemplary embodiment, there is at least one surface mounted
structure proximate each corner of the chip 104 on which the bib
200 may be affixed. In the embodiment illustrated in FIG. 4, the
height of the surrounding decoupling capacitors 108 exceeds the
height of the chip 104. Accordingly, some slack is left in the bib
200 so that it surrounds the chip at about the midpoint of its
thickness.
[0024] Once the bib 200 is mounted, the thermal paste is then
applied onto the top of the chip 104 and/or the inside surface 116
of the cap 112. The cap 112 is then applied to the chip and
substrate surfaces in a conventional manner. As further shown in
FIG. 4, the bib 200 prevents the excess thermal paste 114 from
being displaced and reformed directly atop the surface mounted
components, as well as underneath the chip itself.
[0025] FIG. 5 is a process flow diagram illustrating a method 400
for selective thermal paste deposition and retention on integrated
circuit chip module, in accordance with a further embodiment of the
invention. In block 402, one or more integrated circuit chips and
passive components are joined with the surface of a substrate.
While the passive components (e.g., resistors, capacitors, etc.)
may be arranged on the substrate an any number of configurations,
it will be noted that there should be sufficient structures
surrounding the chip(s) for subsequent mounting and placement of
the bib. Once the devices are formed on the substrate, electrical
testing of the chip(s) and passive components may take place, as
shown in block 404.
[0026] Assuming satisfactory performance of the chip(s) and passive
components, the bib is then positioned around the perimeter of the
chip(s) and adhered to the passive components (e.g., decoupling
capacitors), as shown in block 406. As such, the passive components
to which the bib is mounted serve a dual purpose (i.e., a support
structure as well for electrical performance of the module). Then,
at block 408, a suitable thermally conductive paste (e.g., ATC 3.8)
is applied to the top of the chip(s) and/or the protective cap.
Finally, as indicated at block 410, the protective cap is secured
to the substrate through the application of an adhesive material
such as, for example, Sylgard.RTM. (a silicone elastomer adhesive
available from Dow Corning) to the perimeter of the substrate. A
mechanical retaining assembly, such a spring clip may be applied to
the cap/module during the adhesive curing process. Once cured, the
electrical components of the IC module may be retested to verify
the application of the thermally conductive paste has not degraded
the device performance.
[0027] Through the application of the above described protective
bib, no changes in "rise time" frequency have been observed during
electrical testing subsequent to the application of the thermal
paste and cap attachment, as illustrated by the frequency response
curves in FIG. 6. Moreover, the removal of the protective cap from
module substrate reveals the absence of thermal paste from the
surface of the separately mounted resistors and underneath the
integrated circuit chips.
[0028] While the invention has been described with reference to a
preferred embodiment or embodiments, it will be understood by those
skilled in the art that various changes may be made and equivalents
may be substituted for elements thereof without departing from the
scope of the invention. In addition, many modifications may be made
to adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
* * * * *