U.S. patent application number 09/814589 was filed with the patent office on 2002-09-26 for stress-relieving heatsink structure and method of attachment to an electronic package.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Alcoe, David J., Stutzman, Randall J..
Application Number | 20020135052 09/814589 |
Document ID | / |
Family ID | 25215495 |
Filed Date | 2002-09-26 |
United States Patent
Application |
20020135052 |
Kind Code |
A1 |
Alcoe, David J. ; et
al. |
September 26, 2002 |
STRESS-RELIEVING HEATSINK STRUCTURE AND METHOD OF ATTACHMENT TO AN
ELECTRONIC PACKAGE
Abstract
A stress-relieving heatsink structure and method of forming
thereof for an electronic package, for instance, that including a
semiconductor chip package which is mounted on a wired carrier,
such as a circuitized substrate. The heatsink structure is
constituted from a plurality of base structures which are joined
along slits so as to impart a degree of flexibility to the
electronic package inhibiting the forming of stresses tending to
cause delamination of the package components.
Inventors: |
Alcoe, David J.; (Vestal,
NY) ; Stutzman, Randall J.; (Vestal, NY) |
Correspondence
Address: |
Richard L. Catania, Esq.
Scully, Scott, Murphy & Presser
400 Garden City Plaza
Garden City
NY
11530
US
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
25215495 |
Appl. No.: |
09/814589 |
Filed: |
March 22, 2001 |
Current U.S.
Class: |
257/678 ;
257/E23.087; 257/E23.102 |
Current CPC
Class: |
H01L 2924/0002 20130101;
H01L 2924/0002 20130101; H01L 23/367 20130101; H01L 23/42 20130101;
H01L 2924/00 20130101 |
Class at
Publication: |
257/678 |
International
Class: |
H01L 023/02 |
Claims
What is claimed is:
1. An arrangement for dissipating heat generated by an electronic
package including a circuitized substrate and at least one
semiconductor chip package having a first surface positioned to
face said substrate, said heat-dissipating arrangement comprising:
a heatsink structure including a plurality of discrete base members
being arranged in spaced relationship from an opposite surface of
said at least one semiconductor chip package, said plurality of
separate base members joined in an edge- contacting relationship
with each other so as to form a stress-relieving combination of
said heatsink base members imparting an enhanced flexibility to
said electronic package inhibiting delamination between said
circuitized substrate and said at least one semiconductor chip
package while maintaining the thermal conductivity for heat
dissipation thereof.
2. An arrangement for dissipating heat from an electronic package
as claimed in claim 1, wherein each of said base members comprises
an essentially rigid rectangular base member, said plurality of
base members being located in edge-to-edge positions so as to form
slits therebetween; and connecting means filling said slits for
adhering said plurality of base members together to form said
heatsink structure.
3. An arrangement for dissipating heat from an electronic package
as claimed in claim 2, wherein said connecting means comprises an
adhesive material.
4. An arrangement for dissipating heat from an electronic package
as claimed in claim 3, wherein said adhesive material comprises a
silicone adhesive.
5. An arrangement for dissipating heat from an electronic package
as claimed in claim 3, wherein said adhesive material comprises an
epoxy resin composition.
6. An arrangement for dissipating heat from an electronic package
as claimed in claim 3, wherein said adhesive material comprises a
solder adhesive having a high degree of thermal conductivity.
7. An arrangement for dissipating heat from an electronic package
as claimed in claim 6, wherein said solder adhesive possesses
hierarchial melt temperatures.
8. An arrangement for dissipating heat from an electronic package
as claimed in claim 2, wherein said plurality of base members are
joined through mechanical engaging means located in each of the
slits.
9. An arrangement for dissipating heat from an electronic package
as claimed in claim 8, wherein said mechanical engaging means
comprises snap fits, milled interlocking clearance slots or hinge
structures.
10. An arrangement for dissipating heat from an electronic package
as claimed in claim 1, wherein upstanding spaced fin or pin
elements are formed on each of said base members to assist in the
dispersion and dissipation of heat generated by said electronic
package.
11. An arrangement for dissipating heat from an electronic package
as claimed in claim 1, wherein said base members are each
constituted of aluminum.
12. An arrangement for dissipating heat from an electronic package
as claimed in claim 1, wherein said base members are each
constituted of copper.
13. A method for dissipating heat generated by an electronic
package including a circuitized substrate and at least one
semiconductor chip package having a first surface positioned to
face said substrate, said heat-dissipating method comprising: (a)
arranging a heatsink structure including a plurality of discrete
base members in spaced positions at an opposite surface of said at
least one semiconductor chip; and (b) and joining said plurality of
separate base members imparting an enhanced flexibility to said
electronic package inhibiting delamination between said circuitized
substrate and said at least one semiconductor chip package while
maintaining the thermal conductivity for heat dissipation
thereof.
14. A method for dissipating heat from an electronic package as
claimed in claim 13, wherein each of said base members comprises an
essentially rigid rectangular base member, locating said plurality
of said base members in edge-to-edge positions so as to form slits
therebetween; and filling said slits with connecting material for
adhering said plurality of base members together to form said
heatsink structure.
15. A method for dissipating heat from an electronic package as
claimed in claim 14, wherein said connecting method comprises an
adhesive material.
16. A method for dissipating heat from an electronic package as
claimed in claim 15, wherein said adhesive material comprises a
silicone adhesive.
17. A method for dissipating heat from an electronic package as
claimed in claim 15, wherein said adhesive material comprises an
epoxy resin composition.
18. A method for dissipating heat from an electronic package as
claimed in claim 15, wherein said adhesive material comprises a
solder adhesive having a high degree of thermal conductivity.
19. A method for dissipating heat from an electronic package as
claimed in claim 18, wherein said solder adhesive possesses
hierarchical melt temperatures.
20. A method for dissipating heat from an electronic package as
claimed in claim 13, wherein said plurality of base members are
joined through mechanical engaging structure located in each of the
slits.
21. A method for dissipating heat from an electronic package as
claimed in claim 20, wherein said mechanical engaging structure
comprises snap fits, milled interlocking clearance slots or hinge
structures.
22. A method for dissipating heat from an electronic package as
claimed in claim 13, wherein upstanding spaced fin or pin elements
are formed on each of said base members to assist in the dispersion
and dissipation of heat generated by said electronic package .
23. A method for dissipating heat from an electronic package as
claimed in claim 13, wherein said base members are each constituted
of aluminum.
24. A method for dissipating heat from an electronic package as
claimed in claim 13, wherein said base members are each constituted
of copper.
25. A heatsink structure comprising a plurality of discrete base
members for joining said plurality of separate base members so as
to impart an enhanced degree of flexibility to said base members
relative to each adjoining base member.
26. A heatsink structure as claimed in claim 25, wherein each of
said base members comprises an essentially rigid rectangular base
member, said plurality of base members being located in
edge-to-edge positions so as to form slits therebetween; and said
joining means filling said slits for adhering said plurality of
base members together to form said heatsink structure.
27. A heatsink structure as claimed in claim 25, wherein said
connecting means comprises an adhesive material.
28. A heatsink structure as claimed in claim 27, wherein said
adhesive material comprises a silicone adhesive.
29. A heatsink structure as claimed in claim 27, wherein said
adhesive material comprises an epoxy resin composition.
30. A heatsink structure as claimed in claim 27, wherein said
adhesive material comprises a solder adhesive having a high degree
of thermal conductivity.
31. A heatsink structure as claimed in claim 30, wherein said
solder adhesive possesses hierarchial melt temperatures.
32. A heatsink structure as claimed in claim 26, wherein said
plurality of base members are joined through mechanical engaging
means located in each of the slits.
33. A heatsink structure as claimed in claim 32, wherein said
mechanical engaging means comprises snap fits, milled interlocking
clearance slots or hinge structures.
34. A heatsink structure as claimed in claim 25, wherein upstanding
spaced fin or pin elements are formed on each of said base members
to assist in the dispersion and dissipation of heat..
35. A heatsink structure as claimed in claim 25, wherein said base
members are each constituted of aluminum.
36. A heatsink structure as claimed in claim 25, wherein said base
members are each constituted of copper.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a stress-relieving heatsink
structure for an electronic package, for instance, that includes a
semiconductor chip which is mounted on a wired carrier, such as a
circuitized substrate. Moreover, the invention is also directed to
a method of attaching a stress-relieving heatsink structure to an
electronic package.
[0003] The utilization of heatsink structures which are adapted to
remove and dissipate heat generated by electronic packages, such as
those comprising printed or wired circuit boards mounting one or
more a semiconductor chips is well known in the technology.
Generally, heatsink configurations include either flat cap
structures which are arranged above the semiconductor chip and heat
conductively attached thereto; or heatsinks which are constituted
of relatively thick and stiff base structures having pins or fins
projecting therefrom in a direction or directions facing away from
the electronic package or semiconductor chip so as to afford a good
heat spreading capability while concurrently enabling the low cost
manufacture thereof through the intermediary of suitable extrusion
forming methods.
[0004] Ordinarily, in order to provide good thermal absorption of
heat from the electronic package, the heatsink structure is
adhesively attached through the interposition of a thin layer of a
thermally conductive adhesive. However, depending upon the type of
electronic package, the stiffness of the base portion of the
heatsink structure may prevent achievement of very high reliability
of the electronic package due to a constraining effect produced by
the structure thereof. The constraining effect can contribute to
delamination and higher internal stresses, which can lead to
eventual thermal fatigue of the electronic package components, in
accelerated life testing.
[0005] Flexible electronic packages, (such as may have organic
components in the form of the substrates or carriers mounting the
integrated or printed circuits and forming integrated circuit
boards), are more vulnerable to the constraining effect of the
heatsink arrangement and can benefit by the use of a heatsink which
does not create high stresses in the package and package
interconnections.
[0006] In essence, heatsinks which have a high bending stiffness
can contribute to high stresses during operation of the electronic
package, which causes a significant amount of strain and stress to
be imparted to the thermal adhesive which is employed in order to
attach the heatsink to the electronic package, whereby the relative
deformation encountered among the various components causes failure
in the operation thereof.
[0007] Currently employed heatsinks fail to provide for structures
which are designed to adequately reduce stresses and strains
generated during the operation of the electronic package as a
result of generated heat, and which would tend to prevent
delamination or fatigue of the electronic package components.
[0008] In particular, even present heatsink structures which are
joined to each other fail to provide low stress joining
arrangements in forming the combination thereof which would reduce
stresses and strains to acceptable levels. These known structures
do not address themselves to deriving the advantages which are
obtainable by combining several heatsinks together prior to the
assembly thereof with the electronic package components, which
would require only a single location joining operation to be
utilized during assembly, and a well controlled placement of the
heatsinks relative to each other.
[0009] 2. Discussion of the Prior Art
[0010] Thus, Hamburgen, et al. U.S. Pat. No. 6,034,430 discloses an
integrated thermal coupling for a heat generating device wherein
heatsink structures include fins which are adapted to be
interleaved to provide for enhanced heat dissipation. Although this
provides an extensive degree of thermal contact between two
separable heatsinks, the structure thereof is lightly complex, and
fails to disclose the use of the effects of an adhesive
interconnection between adjoining heatsink components, whereas
contrastingly, the present invention teaches the mitigation of
stress caused through the use of a heat conductive adhesive between
the electronic package components and a composite heatsink
arrangement.
[0011] Chaney, et al. U.S. Pat. No. 5,985,697 discloses heatsink
consisting of a plate-like base member having a plurality of fins
projecting therefrom, and which is adapted to dissipate heat
generated by the electronic package. The structure disclosed in
this patent fails to provide a multi-segmented heatsink arrangement
which is adapted to reduce thermal mechanical stresses of the
heatsink when coupled to the electronic package component.
[0012] Tzu, et al. U.S. Pat. No. 5,973,407 discloses a heat
spreader arrangement which is integrally connected to a
semiconductor package, and wherein a plurality of bumps and
heatsink plate portions are adapted to disperse and dissipate heat
to the exterior environment. There is no disclosure of a segmented
heatsink arrangement which incorporates low-stress interconnections
in order to avoid or reduce to tenable levels and the stresses and
strains encountered during the generation of heat by the electronic
package.
[0013] Similarly, Lee U.S. Pat. No. 5,641,987 discloses a heat
spreader for semiconductor packages which includes different pad
sizes adapted to conjointly dissipate heat generated by the
package. However, as in the previously discussed prior art
publications, there is no low-stress interconnection between
various discrete heatsink segments which are combined to form an
overall heatsink arrangement which would prevent delamination of
the components of the electronic package caused by heat generated
by the package.
[0014] Other patents for example, such as Lester U.S. Pat. No.
5,043,796 disclose multiple component heatsink structures which are
interconnected in various regions so as to provide stress relief
fracture paths. However, the stress-relief interconnections are
merely constituted by reducing the thickness of part of the
heatsink element to provide some bending ability, and does not in
actuality produce a separate components which are adapted to be
combined with other separate components to form a complete
structure.
[0015] Similarly, Leecraft, et al. U.S. Pat. No. 4,296,455 also
discloses a plurality of discrete heatsink components which do not,
in actuality enable the reduction of stresses tending to delaminate
the heatsink structure from the remaining portions of the
electronic package to which they are fastened through the
intermediary of an adhesive material, but which does not provide a
unitarily connected entity.
SUMMARY OF THE INVENTION
[0016] Accordingly, pursuant to the present invention, there is
provided a novel heatsink structure which incorporates a base
structure incorporating stress-relieving slits forming discrete
heatsink segments, whereby there is effectively reduced the
constraining effect of a single large-sized heatsink with no
appreciable loss in the thermal performance of the electronic
package. Through the incorporation of low-stress adhesives, or
possibly in some instances, snap fits, milled interlocking
clearance slots, hinges or other low stress joining structures as
the stress relieving slits provided intermediate various separate
components of the heat sink structure or arrangement, a plurality
of essentially smaller-sized separate heat sinks can be combined
into one larger-sized low-stress heatsink structure which is
pre-assembled and attached to the electronic package to enable the
maximum heat-dissipation therefrom.
[0017] Pursuant to preferred embodiments of the invention, an
advantageous, choice for a low-stress adhesive material which may
be used as connective material in the stress relieving slits
intermediate the various separate heatsink substructures, there may
be provided silicone or epoxy resin adhesives which are potentially
constituted from the same type of material as the adhesive which is
utilized to join the heatsink structure to the electronic package,
such as the printed circuit or wiring board and the electronic
component, such as the semiconductor chip or chips.
[0018] Accordingly, it is an object of the present invention to
provide a novel heatsink structure for an electronic package which
includes stress-relieving slits formed in the heatsink structure to
form a plurality of essentially combinable discrete or separate
smaller heatsink substructure, and which upon being adhesively
attached to each other will provide for a stress-relieving
arrangement while still maintaining good thermal conductivity in
the heat dissipation from the electronic package.
[0019] Another object of the present invention is to provide a
heatsink structure constituted of a plurality of combined
smaller-sized heatsink devices or substructures which are joined
along slitted edges through the intermediary of a low-stress
adhesive or suitable engaging means, which will enable a certain
degree of flexibility to be imparted to the overall heatsink
structures so as to prevent delamination caused by heat-induced
strains and stresses encountered during operation of the electronic
component on which the heatsink is mounted, by a resultant
reduction of the strains due to an enhanced flexibility and
bendability of the heatsink structure.
[0020] Still another object of the present invention is to provide
a method of forming the novel heatsink structure which is
constituted of a plurality of joined or adhesively interconnected
smaller heatsink components or substructures in a stress-relieving
manner while the thermal conductivity of the electronic package is
essentially maintained.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0021] Reference may now be made to the following detailed
description of preferred embodiments of the invention, taken in
conjunction with the accompanying drawings; in which:
[0022] FIGS. 1a and 1b illustrate, respectively, a top plan and
elevational sectional view showing, diagrammatically, a heatsink
structure constructed pursuant to the prior art as bonded to an
electronic package;
[0023] FIGS. 2a and 2b illustrate, respectively, a top plan and an
elevational sectional view of a diagrammatic representation of a
low stress heatsink structure bonded to an electronic package
pursuant to the invention;
[0024] FIGS. 3a and 3b illustrate, respectively, a top plan and an
elevational sectional view of a further embodiment of the inventive
heatsink arrangement, showing solder-filled slits as part of a
low-stress configuration attached to a lower melt solder interface
with an electronic package.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0025] Referring now in specific detail to the drawings, and
particularly FIGS. 1a and 1b, there is illustrated an electronic
package which includes a heatsink in accordance with the prior
art.
[0026] In particular, the electronic package 10 includes a printed
or wired circuit board or card 12 which has a semiconductor chip
package 14 positioned thereon, with the interposition of solder
balls 16 and underfill material (not shown), as is well known in
the technology.
[0027] Arranged above the semiconductor chip package 14, and facing
the surface 18 thereof opposite the side 20 facing the circuit
board or card 12, there is provided a heatsink structure 22 for
dissipating heat generated by the electronic package 10 during
operation thereof.
[0028] The heatsink structure 22, in this instance, is constituted
of a relatively thick unitary base member 24 of generally flat or
planar configuration, preferably constituted of a copper or
aluminum material or composition, which extends in spaced
relationship over and possibly beyond the peripheral confines of
the semiconductor chip package 14. The heatsink structure 22 has
the unitary base member 24 equipped with a plurality of upstanding
spaced fins or pin members 26, which are intended to assist in
further enhancing the dispersing and dissipating of heat from the
electronic package 10. Interposed between the semiconductor chip
package 14 and the facing surface of the heatsink base member 24 is
a suitable adhesive 28, which may be of a heat conductive nature,
such as a silicone or an epoxy resin adhesive, and which may be of
a similar material as an adhesive (not shown) which interconnects
and encapsulates the semiconductor chip package 14 with the
substrate or printed circuit board 12, and the semiconductor chip
package 14 with the base member 24 or heat sink structure 22.
[0029] As may be ascertained from the prior art, during
heat-generating operation of the electronic package 10, and
depending upon the type of electronic package, the stiffness of the
base member 24 of the heatsink structure 22, due to its relatively
rigid or inflexible nature, and the generally flexible or organic
laminated electronic package substrates 12 which are frequently
utilized in this technology, the differences in the bending
properties and possibly coefficients of thermal expansion (CTE) may
cause delamination and a significant loss of reliability of the
electronic package due to the constraining effect caused by the
rigidity of the unitarily constructed heatsink element or structure
22.
[0030] In order to ameliorate the problems encountered in the
employment of a unitary or single heatsink base member 22, which is
inherently of a considerable greater degree of thickness relative
to the remaining components of the electronic package 10, pursuant
to the present invention it has been proposed to provide
stress-relieving slits in a heatsink member, having particular
reference to FIGS. 2a and 2b of the drawings, wherein components
which are similar to or identical with those shown in FIGS. 1a and
1b are identified by the same reference numerals.
[0031] In FIGS. 2a and 2b, as illustrated, the use of stress
relieving slits or grooves 30 between adjoining heatsink base
segments 32, may significantly reduce any strains on the thermal
adhesive which is employed for attaching the heatsink structure 34
to the electronic package 10, in effect the adhesive which bonds
the lower surface 36 of each separate of the base segments 32 of
the heatsink structure 34 to the facing surface 38 of the
semiconductor chip package 14.
[0032] Heretofore, grooving which has been employed in the prior
art as in Lester U.S. Pat. No. 5,043,796, has to some extent
relieved delamination-causing stresses. However, this has not been
adequate to prevent fatiguing of the adhesive material and the
resultant failure in the operation of the electronic package, or at
least in reducing the reliability thereof, because bending
stiffness of the heatsink base 24 was not significantly reduced as
in the present invention.
[0033] In accordance with the present invention, the heat
stress-relieving heatsink component is formed by means of separate
heatsink base segments 32, which are separately produced and then
assembled with each other prior to being positioned on and attached
to the electronic package 10. In this connection, each of the base
segments 32 of the heatsink structure 34 provides a portion of the
generally flat base thereof, analogous to that shown in FIGS. 1a
and 1b, and wherein the smaller segments 32 are initially
preassembled and combined with each other with the edges in the
form of the slits 30 adhesively connected to each other, preferably
by means of a silicone or epoxy adhesive 42 which is heat
conductive so as not to reduce the heat dissipating properties and
characteristics of the entire heatsink structure 34, while
concurrently providing for a stress relieving property which
significantly reduces strains on the thermal adhesive 44 normally
used to attach the lower stress heatsink to the electronic package.
This particular type of slitted construction, and the forming of
separate heatsink segments which are adhesively preassembled into
the overall heatsink arrangement or structure 34, enables the
utilization of a highly-filled thermally-efficient adhesive, such
as a silicone or epoxy resin, for the electronic package and which
generally can tolerate less strain to failure during operation.
[0034] Rather than utilizing an adhesive 42 in the slits 30 between
the heatsink segments 32, it is also possible that the separate
base members 32 of the heatsink structure 34 may be interconnected
along the separating lines or slits 30 through the intermediary of
snap fits, milled interlocking clearance slots, hinges or other
low-stress joining means rather than an adhesive provided at the
stress-relieving slits so as to assemble several smaller-sized heat
sink elements or segments 32 into one large-sized low-stress
heatsink structure 34. However, although this may of course, assist
in reducing the potential for failure due to the generation of
strains or stresses which would tend to delaminate the adhesive
interconnecting the heatsink base 32 to the semiconductor chip
package 14 or components of the electronic package 10, these
alternative mechanical methods may require machining or other
methods of production which may be somewhat more expensive and
complicated in comparison with simply applying a good
heat-conductive adhesive material 42 interconnecting the base
segments 32 of the heatsink structure 34 in the slits 30
thereof.
[0035] In particular, it would be advantageous and inexpensive in
connection with the production, if the adhesive material 42 which
is used as a low-stress component in the stress-relieving slits 30
between the various heatsink segments 32 be constituted of an
adhesive including silicones, potentially of the same type of
adhesive 44 utilized to attach the heatsink base component to the
electronic package 10; in effect, that used to interconnect the
semiconductor chip package 14 with the facing surface of the
heatsink structure 34.
[0036] Pursuant to a further embodiment of the invention, as
disclosed in FIGS. 3a and 3b of the drawings, there is disclosed
the provision of solder-filled slits 50 intermediate the various
base segments 32 forming the overall heatsink structure 34. In this
connection, this type of construction enables the use of a solder
adhesive interface for the attachment of the heatsink. Although
solder is known to frequently fatigue and fracture under strain,
and consequently it is critical to relieve any thermal strains
imposed on a solder interface layer, the present invention provides
for a construction which reduces the strain on the solder
interface. Inasmuch as solder is relatively hard, in comparison
with silicone adhesives, it is thus important to ameliorate the
stiffness of the heatsink base structure, whereby the electronic
package 10 becomes is acceptable as to its reliability and
operation. This is rendered possible through the combination of the
solder adhesive interface 52 in the slits 50 with stress-relieving
features, such as the solder-filled slits of the heatsink
components, inasmuch as the solder possesses a relatively good
thermal conductivity, such that a high-thermal performance heatsink
with low-stress when attached to the electronic package 10 can be
readily attained. In particular, solder with hierarchial melt
temperatures would provide an excellent alternative to adhesives
constituted of silicone, and with the lower-melt solder being also
utilized to attach the low stress heatsink base segments 32 of the
structure 34 to the electronic package 10.
[0037] From the foregoing, it becomes readily apparent that by
means of the slits which are formed in the heatsink arrangement,
whereby a plurality of smaller heatsink elements are preassembled
with each other to form a larger heatsink structure extending over
the entire surface area of the semiconductor chip, and with the
interposition in the slits of either a thermally conductive
adhesive constituted of a silicone, or possibly a solder- type
adhesive as described hereinabove, or mechanical interconnections
this would readily mitigate any formation of strains and stresses
during operation of the electronic package normally tending to
delaminate the package components.
[0038] While the invention has been particularly shown and
described with respect to preferred embodiments thereof, it will be
understood by those skilled in the art that the foregoing and other
changes in form and details may be made therein without departing
form the spirit and scope of the invention.
* * * * *