U.S. patent application number 13/848960 was filed with the patent office on 2014-09-25 for heat spreading layer with high thermal conductivity.
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 Evan G. Colgan, Taryn J. Davis, Chenzhou Lian, Yi Pan, Kamal K. Sikka, Jeffrey A. Zitz.
Application Number | 20140284040 13/848960 |
Document ID | / |
Family ID | 51568264 |
Filed Date | 2014-09-25 |
United States Patent
Application |
20140284040 |
Kind Code |
A1 |
Colgan; Evan G. ; et
al. |
September 25, 2014 |
HEAT SPREADING LAYER WITH HIGH THERMAL CONDUCTIVITY
Abstract
Embodiments of the invention comprise a homogeneous heat
spreading cap element in chip packages to facilitate better heat
spreading and dissipation. The heat spreading cap comprises a
single high-K graphite layer supported by a copper frame for
increased stability and reduced thermal warpage during handling and
operation while minimizing thermal penalty by reducing the amount
of material having a relatively low heat conductivity that is
needed in conventional heat spreading caps.
Inventors: |
Colgan; Evan G.; (Chestnut
Ridge, NY) ; Davis; Taryn J.; (Beacon, NY) ;
Lian; Chenzhou; (Poughquag, NY) ; Pan; Yi;
(Poughkeepsie, NY) ; Sikka; Kamal K.;
(Poughkeepsie, NY) ; Zitz; Jeffrey A.;
(Poughkeepsie, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INTERNATIONAL BUSINESS MACHINES CORPORATION |
Armonk |
NY |
US |
|
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
51568264 |
Appl. No.: |
13/848960 |
Filed: |
March 22, 2013 |
Current U.S.
Class: |
165/185 ;
257/712 |
Current CPC
Class: |
H01L 23/373 20130101;
H01L 2224/32225 20130101; H05K 7/20509 20130101; H01L 25/0655
20130101; H01L 2224/48091 20130101; H01L 24/73 20130101; H01L 23/34
20130101; H01L 23/367 20130101; H01L 2224/73253 20130101; H01L
24/32 20130101; H01L 2224/16225 20130101; H01L 2224/73265 20130101;
H01L 2924/00014 20130101; H01L 2924/00014 20130101; H01L 2224/73265
20130101; H01L 2924/00012 20130101; H01L 2224/32225 20130101; H01L
2224/45015 20130101; H01L 2924/00014 20130101; H01L 2224/45099
20130101; H01L 2224/16225 20130101; H01L 2924/207 20130101; H01L
2924/00012 20130101; H01L 2224/48227 20130101; H01L 2224/32225
20130101; H01L 2224/48091 20130101; H01L 24/16 20130101; H01L
2224/73204 20130101; H01L 2924/00014 20130101; H01L 2924/3511
20130101; H01L 2224/73215 20130101; H01L 23/36 20130101; H01L
2224/48227 20130101; H01L 24/48 20130101; H01L 2224/73204
20130101 |
Class at
Publication: |
165/185 ;
257/712 |
International
Class: |
H01L 23/373 20060101
H01L023/373 |
Claims
1. A cooling system for a semiconductor package comprising: a heat
spreading layer partially encased in a supporting frame, the heat
spreading layer including a perimeter, the supporting frame being
configured to encase the perimeter and an adjacent portion of the
heat spreading layer, defining centrally exposed top and bottom
portions of the heat spreading layer; and a heat generating element
thermally connected to the centrally exposed bottom portion of the
heat spreading layer.
2. The system of claim 1, wherein the semiconductor package is a
flip chip ball grid array package, a flip chip land grid array
package, or a flip chip pin grid array package.
3. The system of claim 1, wherein the semiconductor package is a
wire bonding assembly package.
4. The system of claim 3, wherein the centrally exposed bottom
portion of the heat spreading layer further comprises a centrally
protruding portion connected to a central portion of a top surface
of the heat generating element.
5. The system of claim 1, wherein the heat spreading layer is made
from graphite.
6. The system of claim 5 wherein the heat spreading layer is
positioned to have high thermal conductivity in a first direction
being substantially perpendicular relative to the substrate, and
relatively high thermal conductivity in at least a second direction
substantially parallel relative to the substrate.
7. The system of claim 1, wherein the heat spreading layer is made
from pyrolytic graphite.
8. The system of claim 1, wherein the heat spreading layer is
attached to the supporting frame using an adhesive material.
9. The system of claim 1, wherein the supporting frame is a single
piece having a cavity for encasing the heat spreading layer.
10. The system of claim 1, wherein the supporting frame comprises
at least a first piece and a second piece.
11. The system of claim 10, wherein the first piece and the second
piece of the supporting frame are joined mechanically, by an
adhesive material, and/or by a thermally conductive adhesive
material.
12. The system of claim 1, wherein the supporting frame is made
from a polymer.
13. The system of claim 1, wherein the supporting frame is made
from a metal.
14. The system of claim 13, wherein the supporting frame is made
from copper.
15. The system of claim 1, wherein a top surface of the supporting
frame is flush relative to a top surface of the heat spreading
layer.
16. The system of claim 1, wherein at least a portion of a top
surface of the supporting frame is raised relative to a top surface
of the heat spreading layer.
17. The system of claim 1, wherein an inner perimeter of a top
portion of the supporting frame surrounds the centrally exposed top
portion of the heat spreading layer, and the inner perimeter is
beveled.
18. The system of claim 1, wherein a portion of the top surface of
the supporting frame extends over a portion of the top surface of
the heat spreading layer.
19. The system of claim 1, further comprising a heat dissipating
element thermally connected to a top surface of the heat spreading
layer, the heat dissipating element having a centrally protruding
portion on a bottom surface thereof, wherein the centrally
protruding portion is beveled.
20. The system of claim 1, wherein a top surface and/or a bottom
surface of the heat spreading layer is chamfered.
21. The system of claim 1, wherein a top surface and/or a bottom
surface of the heat spreading layer has rabbet edges.
22. A semiconductor package, comprising: a substrate; a chip
electrically connected to the substrate; a thermal module having a
heat spreading layer partially encased in a supporting frame, the
heat spreading layer including a perimeter, the supporting frame
being configured to encase the perimeter and an adjacent portion of
the heat spreading layer, defining centrally exposed top and bottom
portions of the heat spreading layer, wherein the chip is thermally
connected to the centrally exposed bottom portion of the heat
spreading layer; and a circuit board electrically connected to the
substrate and the chip.
23. The semiconductor package of claim 22, further comprising: a
plurality of the chips electrically connected to the substrate; and
a plurality of the thermal modules corresponding to each of the
chips, wherein each chip is thermally connected to the centrally
exposed bottom portion of each of a plurality of the heat spreading
layers, respectively, of each of the thermal modules.
24. A method for cooling a heat generating element in a
semiconductor package, comprising: partially encasing a heat
spreading layer in a supporting frame, the heat spreading layer
including a perimeter, the supporting frame being configured to
encase the perimeter and an adjacent portion of the heat spreading
layer, defining centrally exposed top and bottom portions of the
heat spreading layer; and thermally connecting a heat generating
element to the centrally exposed bottom surface of the heat
spreading layer.
25. The method of claim 23, wherein the semiconductor package
operates under a hygrothermal condition with a temperature between
approximately -40.degree. C. and 125.degree. C. and relative
humidity of up to 85%.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to the field of controlling
thermal conduction in computer chip packaging, and more
specifically to a heat spreading cap structure having high thermal
conductivity.
BACKGROUND
[0002] Innovations in semiconductor fabrication and packaging
technologies have enabled development of high performance, densely
integrated semiconductor chip modules. The downscaling of chip
geometries and the increase in operating speeds lead to increased
power densities, resulting in more heat generation per unit area.
The increased power density poses practical limitations to the
level of integration density and performance that may be achieved.
The ability to implement chip modules with higher densities and
higher performance is limited primarily by the ability to
effectively cool the chip modules during normal operation. For
instance, as heat is generated by integrated circuit ("IC") chips
during normal operation, cooling structures must be employed to
provide sufficiently low thermal resistance paths between the chips
and ambient air or a circulating liquid coolant to adequately
remove heat and maintain the operating temperature of the chips low
enough to assure continued reliable operation.
[0003] In conventional packaging technologies, chip level packages
can be constructed with one or more chips mounted on a thin
flexible first level package substrate, such as an organic laminate
build up package substrate, using micro solder bump connections,
referred to as C4's (controlled collapse chip connection). The
packages are often bonded to a cap, which provides structural
stability to the package by reducing warpage, and by spreading heat
along a plane, thereby improving the package thermal performance.
The cap, in turn, is attached to a secondary cooling structure,
such as a heat sink or a liquid cooling system.
[0004] Referring now to FIG. 1, a flip chip ball grid array (BGA)
package 100, according to the prior art, comprises a chip die 112
having an operational surface mounted onto a substrate 106 via a
series of C4's 108 encased in an underfill layer 110. These
components are operatively connected to a circuit board 102 via a
separate series of solder balls 104. The die 112 is said to be
flipped because its operational connections face down towards the
substrate 106 and the circuit board 102, and its other side is
connected to a heat sink 140 via a protective heat spreading cap
114. Several layers of the package 100 are connected using layers
of material, including, for example, the thermal interface material
(TIM1) 132 connecting the die 112 to the cap 114, the adhesive
layer 130 connecting the cap 114 to the substrate 106, and the
thermal interface material (TIM2) 134 connecting the cap 114 the
heat sink 140.
[0005] In conventional implementations, the heat spreading cap 114
may be made from copper, having a thermal conductivity of 400
W/m-.degree. C., at 300.degree. K. Although copper has relatively
high structural stability and extends that stability to the package
100, it is not the most thermally conductive material available.
Some forms of graphite, for example, have much higher thermal
conductivity across at least one spatial plane. Other forms of
graphite exhibit thermal conductivity above 1200 W/m-.degree. C.
These materials generally are referred to as high-k materials, or
high-k graphite.
[0006] According to an aspect of the prior art (for example, as
disclosed by U.S. Pat. No. 6,758,263 B2 entitled "HEAT DISSIPATING
COMPONENT USING HIGH CONDUCTIVE INSERTS"), a heterogeneous planar
graphite element includes a high-conductivity graphite layer having
a cavity for housing an insert. The graphite layer exhibits high
thermal conductivity in the x and y planes, but low thermal
conductivity in the z plane. The insert layer has relatively higher
thermal conductivity across the z plane, but not across the x or y
planes.
[0007] Traditional designs and methods in the prior art face
significant challenges, particularly because known structures using
high-k material exhibit weak structural stability, and experience
warpage under normal operating temperatures. This warpage leads to
device defects and even to device failure. In fact, the relative
instability of these structures also makes more prone to damage
during manufacturing processes. Furthermore, prior art solutions
using graphite employ one or more heterogeneous layers, adding to
device complexity but taking advantage of graphite's thermal
conductivity in a limited way.
[0008] Therefore, it is desirable to manage heat spreading and
dissipation in semiconductor packaging technology by taking
advantage of the relatively high thermal conductivity of available
material, such as graphite, while at the same time maintaining
structural integrity of the package and its constituent
components.
SUMMARY
[0009] Embodiments of the invention include a cooling system for a
semiconductor package comprising a heat spreading layer partially
encased in a supporting frame along an outer perimeter, the
supporting frame encasing the perimeter and an adjacent portion of
the heat spreading layer to define centrally exposed top and bottom
portions of the heat spreading layer; and a heat generating element
thermally connected to the centrally exposed bottom portion of the
heat spreading layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Elements of the figures are not necessarily to scale and are
not intended to portray specific parameters of the invention. For
clarity and ease of illustration, scale of elements may be
exaggerated. The detailed description should be consulted for
accurate dimensions. The drawings are intended to depict only
typical embodiments of the invention, and therefore should not be
considered as limiting the scope of the invention. In the drawings,
like numbering represents like elements.
[0011] FIG. 1 is a cross sectional front elevational view of a flip
chip ball grid array package assembly, according to the prior
art;
[0012] FIG. 2 is a partial cross sectional front elevational view
of a flip chip package assembly, having a heat spreading layer
encased in a supporting frame, wherein the supporting frame extends
over a portion of the heat spreading layer, according to an
embodiment of the disclosed invention;
[0013] FIG. 3 is a cross sectional front elevational view of the
flip chip package assembly depicted in FIG. 2, and further depicts
a heat sink, according to an embodiment of the disclosed
invention;
[0014] FIG. 4 is a cross sectional front elevational view of the
flip chip package assembly depicted in FIG. 2, wherein the
supporting frame comprises a plurality of interconnected pieces,
according to an embodiment of the disclosed invention;
[0015] FIG. 5 is a cross sectional front elevational view of the
flip chip package assembly depicted in FIG. 2, wherein the
supporting frame comprises a plurality of interconnected pieces,
according to an embodiment of the disclosed invention;
[0016] FIG. 6 is a partial cross sectional front elevational view
of a flip chip package assembly, having a heat spreading layer
encased in a supporting frame, wherein the supporting frame extends
over a portion of the heat spreading layer, according to an
embodiment of the disclosed invention;
[0017] FIG. 7 is a partial cross sectional front elevational view
of a flip chip package assembly, having a heat spreading layer
encased in a supporting frame, wherein the edges of a top surface
of the heat spreading layer are chamfered, and a top surface of the
supporting frame is flush with a top surface of the heat spreading
layer, according to an embodiment of the disclosed invention;
[0018] FIG. 8 is a partial cross sectional front elevational view
of a flip chip package assembly, having a heat spreading layer
encased in a supporting frame, wherein the edges of a top and a
bottom surface of the heat spreading layer are chamfered, and a top
surface of the supporting frame is flush with a top surface of the
heat spreading layer, according to an embodiment of the disclosed
invention;
[0019] FIG. 9 is a partial cross sectional front elevational view
of a flip chip package assembly, having a heat spreading layer
encased in a supporting frame, wherein the edges of a top and
bottom surface of the heat spreading layer are chamfered, and a top
surface of the supporting frame is flush with a top surface of the
heat spreading layer, according to an embodiment of the disclosed
invention;
[0020] FIG. 10 is a partial cross sectional front elevational view
of a flip chip package assembly, having a heat spreading layer
encased in a supporting frame, wherein the edges of a top surface
of the heat spreading layer are modified to form a rabbet, and a
central portion of a top surface of the supporting frame is flush
with the top surface of the heat spreading layer, according to an
embodiment of the disclosed invention;
[0021] FIG. 11 is a partial cross sectional front elevational view
of a wire bonding chip assembly package, having a heat spreading
layer encased in a supporting frame, wherein the supporting frame
extends over a portion of the heat spreading layer, and central
portion of a bottom surface of the heat spreading layer is
connected to a central portion of a chip, according to an
embodiment of the disclosed invention;
[0022] FIG. 12 is an aerial view of a multi-core processor having a
series of heat spreading layers encased in a supporting frame,
according to an embodiment of the disclosed invention; and
[0023] FIG. 13 is a partial cross sectional front elevational view
of the multi-core processor depicted in FIG. 12.
DETAILED DESCRIPTION
[0024] Referring now to FIG. 2, a subset 200 of a flip chip
package, according to an embodiment of the disclosed invention,
comprises a chip die 112 mounted onto a substrate 106 via a series
of C4's 108 encased in an underfill layer 110. A top surface of the
chip die 112 is connected to a lid comprising a homogeneous,
thermally conductive heat spreading layer 114a housed within a
supporting frame 114b. A bottom surface of the heat spreading layer
114a is connected to the top surface of the chip die 112 via a
thermal interface material ("TIM1") 132. A bottom surface of the
supporting frame 114b is connected to the top surface of the
substrate 106 via an adhesive layer 130. The heat spreading layer
114a and the interior cavity of the supporting frame 114b are also
connected via an adhesive layer 136. The purpose the adhesive layer
136 is, in part, to form a strong interaction between the heat
spreading layer 114a and the supporting frame 114b, and to maintain
the integrity of these two components, particularly in light of
structural stresses, such as heat fluctuations, exerted upon the
chip package during manufacturing and operation. One example of the
material that can be used to form the layer 136 is epoxy based
adhesive.
[0025] Further referring to FIG. 2, the supporting frame 114b is
formed as a single piece, as is the heat spreading layer 114a. It
is not necessary to bond these two components via the adhesive
layer 136, particularly if the supporting frame 114b is molded onto
and around the heat spreading layer 114a during the fabrication
process. According to an aspect of the disclosed invention, the
heat spreading layer 114a is made from a material having relatively
high thermal conductivity, such as graphite, some forms of which
exhibit conductivity above 1200 W/m-.degree. C.
[0026] The graphite heat spreading layer 114a is effective in
spreading heat generated by the chip die 112 and its surrounding
components across the z plane, and at least one of the x or y
planes. By using a high-k material such as graphite, the heat
spreading layer 114a provides greater heat spreading and
dissipation compared to the prior art where a customary choice of
chip cap/lid material is copper. In fact, the graphite heat
spreading layer 114a has double the thermal conductivity of copper
given an equal shape and thickness. Consequently, it is a suitable
choice for forming the heat spreading layer 114a.
[0027] According to an aspect of the disclosed invention, the
graphite heat spreading layer 114a may be formed using two smaller
graphite pieces joined at two adjacent edges by an adhesive (not
shown) to form a single planar graphite layer. Each pyrolytic
graphite piece may be grown to a thickness of about 25 mm, where
its high thermal conductivity is in the horizontal plane and its
low thermal conductivity is in the vertical, or growth, direction.
Thereafter, each piece is orientated such that the low thermal
conductivity of the graphite is in the x direction. A 50.times.50
mm graphite heat spreader may be constructed by cutting out two
pieces that are 25 mm tall, 4 mm thick, and 50 mm long where the
thermal conductivity is high in the 4 mm and 50 mm directions.
These pieces are glued together side-by-side (i.e. by joining their
respective 4.times.50 mm faces) to produce the 50.times.50.times.4
mm single, planar layer heat spreader. Other embodiments of the
invention may have additional pieces in the single planar layer and
oriented and joined in a manner different from the described
configuration, without departing from the scope or the spirit of
the invention.
[0028] Although graphite has desirable high thermal conductivity,
it is generally susceptible to thermal warpage and cracking or
breaking during device operation. Failure of the heat spreading
layer 114a due to warpage in typical operational conditions may be
virtually eliminated by encasing it in the supporting frame 114b.
According to an embodiment of the invention, the supporting frame
114b is made from copper, and encompasses the side, and parts of
the top and bottom surfaces of the layer 114a, leaving a central
portion of both the top and bottom surfaces of the graphite
exposed. By retaining an exposed portion of graphite, the heat
spreading layer 114a remains twice as effective as conventional
copper caps in thermal conductivity at the exposed area. The
supporting frame 114b gives the heat spreading layer 114a
sufficient rigidity at its outer surfaces and edges without
creating a thermal penalty at its exposed regions.
[0029] Other embodiments may employ other metals, such as stainless
steel, or polymers that are sufficiently strong to provide
structural stability to the highly conductive layer 114a.
[0030] Referring now to FIG. 3, a subset 300 of a flip chip package
is similar to the elements recited above in connection with FIG. 2,
wherein like elements have been similarly marked. Additionally, the
subset 300 comprises a heat sink 140 having a bottom surface
contoured to fit into the opening of the exposed area of the top
surface of the heat spreading layer 114a and the top surface of the
frame 114b, via a TIM2 layer 134. Contouring the bottom surface of
the heat sink 140 to the top surface of the lid is beneficial
because it fills a gap that would otherwise form between the heat
sink 140 and the top surface of the heat spreading layer 114a due
to the asymmetrical shapes of the two surfaces. Without contouring
the bottom surface of the heat sink 140, the gap may be filled with
a TIM2 layer, a solution that likely would create an increased
thermal penalty.
[0031] Referring now to FIG. 4, a further embodiment of the
disclosed invention comprises a subset 400 of a flip chip package,
as described and depicted in FIG. 2. Additionally, rather than
using a single-piece supporting frame (the supporting frame 114b as
shown in FIG. 2), the supporting frame of the subset 400 comprises
a top frame 114c and a foot frame 114d, joined at a junction point
114e. The two layers may be joined using an adhesive layer (not
shown), or mechanically. Embodiments of the disclosed invention may
comprise top frames 114c and foot frames 114d made from, for
example, copper or stainless steel.
[0032] Further referring to FIG. 4, the design of the two-piece
supporting frame (114c and 114d) may be used where manufacturing
considerations make it less desirable to form a single piece frame.
For example, it may not be feasible to implement a molding
mechanism that would form a single-piece frame around the layer
114a due to equipment cost, or the unavailability of a polymer
ideal for manufacturing a molded frame.
[0033] Referring now to FIG. 5, a subset 500 of a flip chip
package, according to an embodiment of the disclosed invention,
comprises the elements recited and described with respect to FIG.
4, except that the junction point 114e between the top frame 114c
and the foot frame 114d is vertically aligned with the outer edges
of the heat spreading layer 114a, and the foot frame 114d forms an
"L" shape in a cross sectional view.
[0034] Further referring to FIGS. 4 and 5, the position of the
junction point 114e may be changed according to cost, ease of
design, and other manufacturing considerations, without departing
from the spirit and scope of the disclosed invention.
[0035] Referring now to FIG. 6, a further embodiment of the
disclosed invention comprises a subset 600 of a flip chip package,
as described in connection with FIG. 2. In the disclosed
embodiment, the supporting frame 114b is a single piece having a
top portion that is substantially thinner than the side or foot
portions of the structure. Moreover, the top portion of the
supporting frame 114b extends onto the top surface of the heat
spreading layer 114a at a fraction of the distance it covers on the
bottom surface of the heat spreading layer 114a. Consequently, the
disclosed embodiment allows for greater spreading and dissipation
of heat generated by the chip die 112 by allowing a larger surface
area of the heat spreading layer 114a to connect to a heat
sink.
[0036] Referring now to FIG. 7, a further embodiment of the
disclosed invention comprises a subset 700 of a flip chip package,
as recited and described with respect to FIG. 2. In the depicted
embodiment, the top surface of the heat spreading layer 114a is
chamfered such that the frame 114b extends over a portion of the
layer 114a. The top surface of the supporting frame 114b is flush
with a central portion of the top surface of the heat spreading
layer 114a, and extends over its chamfered edges. The bottom
surface of the heat spreading layer 114a is substantially flat.
Chamfering the heat spreading layer 114a increases the surface area
at which the supporting frame 114b contacts the heat spreading
layer 114a, improving the supporting frame's 114b grip, without
necessarily reducing the surface area of the heat layer 114a that
remains exposed. Since the exposed portion of the heat spreading
layer 114a contacts the heat sink 140, it is desirable to maintain
as much contact area as possible. Moreover, according to the
disclosed embodiment, the heat sink 140 has a flat bottom surface,
since the layer 114a is flush with the supporting frame 114b.
[0037] Referring now to FIG. 8, a further embodiment of the
disclosed invention comprises a subset 800 of a flip chip package,
as recited and described with respect to FIG. 2. In the depicted
embodiment, the heat spreading layer 114a is chamfered along its
top surface, and housed within the supporting frame 114b, as
depicted in FIG. 7, and described in connection therewith.
Additionally, the bottom surface of the heat spreading layer 114a
is also chamfered along its outer edges, with the supporting frame
114b extending over the chamfered edges. In the depicted
embodiment, the chamfered surface on the top surface of the heat
spreading layer 114a is larger than the chamfered surface of the
bottom surface.
[0038] Referring now to FIG. 9, a further embodiment of the
disclosed invention comprises a subset 900 of a flip chip package,
as recited and described with respect to FIG. 2. Furthermore, in
the depicted embodiment, the top and bottom surfaces of the heat
spreading layer 114a are symmetrically chamfered and encased by the
supporting frame 114b. The top surface of the supporting frame 114b
is flush with a central portion of the top surface of the heat
spreading layer 114a.
[0039] Referring now to FIG. 10, a further embodiment of the
disclosed invention comprises a subset 1000 of a flip chip package,
as recited and described with respect to FIG. 2. Furthermore, in
the depicted embodiment, the top surface of the heat spreading
layer 114a is processed to form rabbet edges, and encased in the
supporting frame 114b, such that the supporting frame 114b extends
over the rabbet edges. Moreover, the top surface of the supporting
frame 114b is flush with a central portion of the top surface of
the heat spreading layer 114a.
[0040] Referring now to FIG. 11, a further embodiment of the
disclosed invention comprises a subset 1100 of a wire bonding chip
assembly package similar to the flip chip assembly package depicted
in FIG. 6, wherein like elements are similarly referenced. However,
according to the depicted embodiment, the heat spreading layer 114a
further comprises a protruding central portion on its lower
surface, whereby the heat spreading layer 114a connects to a
central portion of a top surface of the chip 112. The chip 112 is
operatively connected to the substrate layer 106 via a plurality of
wire connections 142, with the active side of the chip 112 facing
the heat spreading layer 114a. According to the depicted
embodiment, the heat spreading layer 114a is in contact with a
central region of the top surface of the chip 112 so as to provide
space for the wire connections 142 in a typical wire bonding
package. The wire connections 142 may be encapsulated in a molding
compound.
[0041] Although the embodiments depicted in FIGS. 2-11 reference an
adhesive layer 136 connecting the heat spreading layer 114a to the
supporting frame 114b (or to the top frame 114c and the foot frame
114d in embodiments having a two-piece frame), forming the adhesive
layer 136 is not necessary to practice the invention. Whether the
adhesive layer 136 is used and at what thickness may be varied
without departing from the spirit or the scope of the disclosed
invention.
[0042] Furthermore, although the embodiments of the disclosed
invention depicted in FIGS. 2-10 are based primarily on a flip chip
package, it will be understood by a person of ordinary skill in the
art, in light of the present disclosure, that the features of the
depicted embodiments (including, without limitation, the shape of
the heat spreading layer 114a or the supporting frame 114b) can be
incorporated into corresponding embodiments using a wire bonding
assembly package, as described with respect to FIG. 11, without
departing from the spirit or scope of the disclosed invention.
[0043] In addition, although the embodiments of the disclosed
invention depicted in FIGS. 2-11 are discussed in reference to the
package 100 using BGA interconnections between the substrate 106
and the circuit board 102, as depicted in FIG. 1, these embodiments
can be incorporated into a land grid array (LGA) package or a pin
grid array (PGA) package. In contrast to a BGA package, wherein the
substrate 106 is electrically connected to the circuit board 102
via a grid of solder ball connections 104, LGA packages use surface
contact areas on the underside of the substrate 106 to connect to a
corresponding grid of contacts on the circuit board 102. The
connection may be implemented using a variety of methods such as
LGA sockets, or solder paste. The substrate 106 surface contacts in
LGA packages are relatively flat compared to the solder ball
connections in BGA packages. In PGA packages, the surface contacts
on the underside of the substrate 106 are not flat, but instead are
pin shaped protrusions arranged in an array, and may connect to a
socket mounted on the circuit board 102.
[0044] Furthermore, although most of the disclosed embodiments
depict a single-piece frame, it will be understood by a person of
ordinary skill in the art that the multi-pieced frames, such as
those depicted in FIGS. 4 and 5, may be employed in the other
depicted embodiments, and any other embodiments as claimed, without
departing from the spirit or scope of the disclosed invention.
[0045] Referring now to FIG. 12, a multichip module ("MCM") 1200
comprises four chips 112 (not shown) mounted onto a substrate layer
1200 (via, for example, a flip chip package) and thermally
connected to respective heat spreading layers 114a, wherein the
heat spreading layers 114a are encased in a supporting frame 114b.
As described with respect to other embodiments of the invention
(and FIGS. 4 and 5 in particular), above, the supporting frame may
be formed as a single piece through, for example, a molding
manufacturing process using a polymer; or it may be formed as
multiple pieces using additional manufacturing methods, such as a
high pressure metal press. According to one embodiment, the
supporting frame 114b may comprise a top frame and a foot frame
(not shown), similar to similarly referenced components depicted in
FIGS. 4 and 5.
[0046] Referring now to FIG. 13, the multichip module ("MCM") 1200
comprises additional sets of components beneath top surfaces of the
supporting frame 114b and heat spreading layers 114a depicted in
FIG. 12. According to the depicted embodiment, each set of
components in the MCM 1200 is similar to the embodiment shown in
FIG. 6, wherein like elements have been similarly referenced.
According to the embodiment depicted in FIG. 13, each shared
portion of the supporting frame 114b situated between each pair of
chips 112 (making a total of four shared portions) is a continuous
portion of the entire supporting frame 114b structure. According to
related embodiments, each heat spreading layer 114a may be encased
by a corresponding supporting frame 114b, wherein the supporting
frames 114b are thermally or mechanically joined to one another to
form the MCM 1200.
[0047] The disclosed invention, including the depicted embodiments,
employ a single high-k layer supported by a frame having a stronger
structural stability. By using a single graphite layer, for
example, the disclosed invention allows for high heat dissipation
across at least two planes, including the z plane, and at least the
x or y planes. Consequently, the disclosed invention allows for
effective thermal conduction overall across the entirety of the
heat spreading layer, without sacrificing structural integrity or
incurring a thermal penalty by covering the high-k material with
another material having relatively low thermal conductivity.
Embodiments of the disclosed invention increase the thermal
conductivity of semiconductor packages in which they are employed,
and allow for reliable operation in hygrothermal operating
conditions, which include temperatures between -40.degree. C. and
125.degree. C., and as much as 85% relative humidity.
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