Note: Descriptions are shown in the official language in which they were submitted.
~3~
This invention relates generally to heat exchange of an electrical
article and more particularly to coollng an integrated circuit chip.
The temperature of integrated circuit chips mus~ be ]cept below speci-
fied limits to ensure proper function, reliability and useul life. The trend
in integrated circuit technology is toward large scale integration which results
in increased functions per chip. Also, system designers are molmting chips
closer together (high density packaging) to minimize propagation delays in the
circuit interconnections. As a result of the foregoing, heat is not only in-
creased for each chip but is also concentrated due to the closely mounted chips.
Cooling of these chips is a problem.
Cooling of high density packaging has been achieved by placing a
liquid cooled~ cold plate in direct contact with a circuit package. A limita-
tion of this is that the circuit componen*s have various heights and shapes.
A compliant interface has been used between the cold plate and the circuit com-
ponents to accommodate these variations. The interface is heat conductive and
electrically insulative and comprises a paste and film.
A limitation of this compliant interface is that it has high thermal
resistance and does not spread *he heat uniformly. ~oreover, if the paste
breaks down ~chemically), the temperature of the components may rise to unde-
sirable levels.
The foregoing illustrates limitations of the known prior art. Thus,
it is apparent that it would be advantageous to provide an alternative directed
to overcoming one or more of the limitations as set forth above. Accordingly~
a suitable alternative is provided including features more fully disclosed here-
inafter.
In one aspect of the present invention, this is accomplished by pro-
\ viding an apparatus for cooling integrated circuit chips comprising a cold plate;
,:
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a first film of paste in contact with said plate, said first film
being heat conduc-tive and elecL~rically insula.tive; a second film
in ~ontact with said firs-t film, said second fil.m haviny a pre
determined array of interconnected me~.allic pads; a third film
in contact with said second filml said third film being heat
conductive and el.ectrically insulative, said first, second and
third films to~ether comprising a compliant mat; a substrate
having a plurality of circuit packages including integrated cir-
cuit chips in a predetermined array corresponding to said array
of metallic pads; and each of said circuit packages being in con~
tact with said third film adjacent an associa-ted metallic pad.
The invention will now be described in greater detail
with reference to the accompanying drawings, in which:
Figure 1 is a perspective view diagrammatically illus-
trating apparatus for cooling integrated circuit packages carried
by substrates;
Figure 2 is a side view illustrating an embodiment of
the invention;
Figure 3 is a plan view illustrating an e-tched configur-
~0 ation of a metallic film used in the invention;
E`igure 4 is a perspective view to an enlarged scaleillustrating a portion of the etched film of Figure 3 and a por-
tion of an associated substrate;
Figure 5 is a cross-sectional side view illustrating an
embodimen~ of the various layers of this invention and an asso-
ciated substrate; and
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36~
Figure 6 is plan view illustrating an embodiment of a
substrate and a predetermined array of integra-ted circuit packages
includi~g a superimposed correspondin~ array of pads formed on the
etched film.
Apparatus for use in coolin~ integrated circuit chips is
generally designated 10 in Figure 1, and includes a well-known
cold plate 12 of a suitable material such as aluminum having a
~irst portion 12a connected and sealed to a second opposed portion
12b. An inlet port 14 is connected to an ou-tlet port 16 by an
exemplary conduit 18, extending through cold plate 12 in a manner
suitable for conducting a fluid, such as cold water, -therethrough
so as to avoid leakage within cold plate 12. A pair of openings
20 forme~ through cold plate 12, are provided to accommodate
electrical connectors between a pair o~ well-known substrates
mounted on opposite portions of cold plate 12. The substrates
and known associated integrated circuit packages connected thereto,
appear in the following discussion in greater detail.
A compliant mat 21 r Figures 1 and 2, is in contac-t with
side each 12a and 12b. Each mat 21 comprises a first film of
paste 26, which adheres to portions12a, 12b. Paste 26 is a com-
mercially available heat conductive paste. A second, metallic
film 28 which may be aluminum but is preferabl~ a ~ilm of copper
adheres to paste ~6 and is laminated to a third film 30 by a well-
known process called *MICR~CLAD. Third film 30 is a commercially
available plastic material and may be the product *TEDLAR/ a
polyvinylfluoride, but is preferably the product *KAPTON, a poly-
amide. The laminated second and third films 28, 30, respectively,
* Trade Mark 3
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are sold by Fortin Laminating Co. of Sylmar, California, U.S.A.
The thickness of the paste 26 is about .040 inches, the thickness
of the copper 28 is about .001 inches, and the thickness o~ the
polyamide 30 is about .001 inches.
A well-known substrate 32 associated with por-tions 12a,
12b of cold plate 12 is shown in Figure 2. Each substrate 32
includes a plurali-ty of co~nercially available integrated circuit
packages 34 which may be of varying shapes and sizes. As it is
well known, such substrates 32 are urged into contact with cold
plate 12 for cooling packages 34. Substrates 32 are maintained
connected to plate 12 by bolts or some suitable means and are
electrically interconnected by connections extending through open-
ings 20.
Since mat 21 is compliant, the various shaped and sl~ed
packages 34 are able to make contact with a portion of mat 21
at film 30 and therefore the~mal conducti~ity via mat 21 is
assured. In order to limit stiffness of mat 21, metallic film
28 is etched, by a suitable process, to a prede-termined array
having a plurality of metallic pads 36 interconnected by metallic
~0 branches 38, see Figure 3. The invention contempla-tes that the
array of interconnected pads 36 may vary from that shown in the
drawings. Also, it is anticipated that it may be desired to i
interconnect less than all the pads 36~ In this manner, as illus-
trated in Figure 4, metallic portions 40 of film 28 are etched
away to e~pose film 30 thus substantially reducing the stiffness
of mat 21. As a result of the etched removal of metallic portions
40, pads 36 and interconnecting arms 38 of ~ilm ~8 remain to
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provide an arra~ suitable for improving a spread of heat Elux
through mat 21.
Packages 34 are usually Eoxmed of an insula-tor material
such as Alumina or Berylia and include integrated circuit chips
42 imbedded therein, as is well known. These packages 34 are
provided on substrate 32 in a predetermined array corresponding
to the array of pads 36, see Figures 4, 5 and 6. In this manner,
a metallic pad 36 is adjacent a respective package 34. I'hus, heat
generated by a chip ~2 is conducted through packa~e 34, film 30,
film 28, paste 26, cold plate 12 and is eventually carried from
cold plate 12 by fluid such as cold water being forced -through
conduit 18.
Si~nificantly, heat may vary between each package 34,
therefore, the interconnecting branches 38, aid in spreading heat
between various pads 36 thus promoting uniform thermal distribu-
tion of mat 21.
In addition to removing stiffness -from mat 21, etching
exposes portions of film 28 thus permit-ting visual inspection for
bubbles, or air pockets, in paste 26 which are not desired since
they are insulative rather than conductive. The copper branches
38 which interconnect the copper pads 36 offer an al-ternat~ ther-
mal path between packages 34~ The alternate pa-th concep-t is bene-
ficial especially where all of the chips ~2 are not dissipating
similar power. Temperature distribution will be substantially
unified in paste 26 and the life of paste 26 will therefore be
prolonged.
6~V
The foregoing has described apparatus for cooling inte-
grated circuit chips which are in contact with a compliant mat
including a thermal paste, a metallic film for promoting -the even
distribution of heat flux through film 21 and another film for
making contact with the integrated circuit packages.
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