High conduction flexible fin cooling module

An apparatus for removing heat from a heat generating device. The apparatus includes at least one heat conductive finned thermal device insert including a base having at least one first fin, and preferably haing a plurality of first fins, on a first surface and a second surface which is flat and a heat conductive second thermal device, preferably a cooling hat, having a plurality of second fins. The first fins are interspersed with the second fins. At least one of the first and second fins is of a thermally conductive, flexible material so that a gap otherwise existing between the interspersed fins is substantially eliminated. Finally, at least a portion of the first and second fins are biased against one another.

BACKGROUND OF THE INVENTION 
This invention relates to conduction cooling of small, flat, heat 
generating devices such as integrated circuit (IC) chips, and more 
particularly, to an improved cooling device having a very low thermal 
resistance path between the heat generating devices and heat sink. 
The introduction of large scale integration (LSI) and very large scale 
integration (VLSI) at the chip level and very large scale integration at 
the module level by packaging multiple chips on a single multilayer 
substrate has significantly increased both circuit and power densities. As 
a consequence, there arises the need to remove heat flux densities on the 
order of 1000kw/square meter at the chip level. To remove these high heat 
flux densities, there have been proposed various means of dissipating the 
heat. One limitation is that the cooling fluid (e.g., water) cannot come 
into direct contact with the chips or the area wherein the chips are 
mounted. Thus, a cooling hat must be incorporated between the chips and 
fluid which may be contained in a detachable or integral cold plate. 
As VLSI chips increase in circuit density, switching speed and 
corresponding power, the thermal resistance of heat conduction systems, 
wherein an internal thermal device insert is placed between the chips and 
cooling hat, must be further reduced. In the thermal conduction module of 
Chu et al. U.S. Pat. No. 3,993,123, the internal thermal device insert is 
a piston which contacts the chip at one point. The thermal conduction 
module is very useful and successful in VLSI systems of the present but is 
not easily extendable to future high powered systems in all applications. 
In the present state of the art there are many structures for achieving 
enhanced heat transfer Among these are intermeshed fin structures wherein 
the internal thermal device insert has substantially rigid fins which mate 
with corresponding fins in the cooling hat. One such fin structure is that 
disclosed in Horvath et al. U.S. patent application Ser. No. 198,962, 
filed May 26, 1988, the disclosure of which is incorporated by reference 
herein. These structures have the potential to provide improved thermal 
performance over single-surface structures, such as the piston in the 
thermal conduction module, because they comprise means for increasing the 
heat transfer area between the internal thermal device insert, which 
contacts the chip, and the cooling hat. Consequently, the thermal 
resistance between the chip and the cooling hat is lowered. 
An inherent feature of these substantially rigid fin structures is that 
there will always be a gap, sometimes relatively large, between the 
intermeshed fins to accommodate chip tilt. This gap may be compensated by 
side-biasing or by filling the gap with a compliant, thermally conductive 
medium such as disclosed in Horvath et al. While such a fin structure does 
provide a low thermal resistance, the thermal resistance of the structure 
may be decreased by decreasing or, more preferably, substantially 
eliminating this gap. 
An alternative structure has been proposed in Mansuria et al. U.S. Pat. No. 
4,263,965 wherein a plurality of thermally conductive thin leaf shaped 
members are positioned within mating recesses of a cooling hat. Each of 
the thin leaf shaped members is independently spring-loaded against the 
chip. Chip tilt is accommodated at the chip-to-leaf interface. Thus, this 
design often times results in line-contact of the thin leaf shaped members 
against the chip, leading to a decrease in thermal efficiency of the 
module. Further, and perhaps most importantly, the leaf shaped members, 
while being thin, are nevertheless rigid as are the mating recesses of the 
cooling hat. Due to manufacturing tolerances, there will always be a 
considerable gap between the leaf shaped members and the cooling hat, 
thereby contributing to increased thermal resistance. 
It has been proposed in certain structures to make the fins out of a 
flexible material 
Thus, in Lipschutz U.S. Pat. No. 4,498,530, a plurality of flexible leaf 
elements are sandwiched between rigid spacer elements. The end result is a 
relatively rigid package, which is placed between the chip and the cold 
plate. Due to the fact that the flexible elements do not make good thermal 
contact with their corresponding flexible elements, the thermal resistance 
of this arrangement is unacceptably high. Also, since the entire structure 
is separate and distinct from the cold plate, an additional thermal 
resistance (i.e., arising from the interface between the cold plate and 
the structure) is included. 
Tinder U.S. Pat. No. 4,707,726 discloses a heat sink having a channel 
therein and a plurality of semiconductor devices which are positioned 
within the channel. The semiconductor devices are side-biased against the 
side of the channel by a flexible member. 
Berg U.S. Pat. No. 4,447,842 discloses a thermal device in contact with a 
chip. The thermal device has flexible fins which fit into channels of a 
cooling module. The cooling module is fitted with an expansible conduit 
which, upon expansion, causes the flexible fins to be forced against the 
sides of the cooling module, thereby aiding in the cooling of the chip. 
Hanlon U.S. Pat. No. 4,190,098 discloses a cooling device for cooling a 
plurality of semiconductor devices. The cooling device comprises flexible 
fins which fit into the channels formed by the semiconductor devices. 
Notwithstanding the previously described state of the art, there remains a 
need to increase the power dissipation capability of the cooling 
arrangement so as to be able to accommodate higher power chips. 
It is thus a primary object of the present invention to have an improved 
cooling arrangement with increased power dissipation capability and 
decreased thermal resistance. 
This and other objects of the invention will become more apparent after 
referring to the following description considered in conjunction with the 
accompanying drawings. 
BRIEF SUMMARY OF THE INVENTION 
The object of the invention has been achieved by providing, according to 
the invention, an apparatus for removing heat from a heat generating 
device comprising: 
at least one heat conductive thermal device insert comprising a base having 
at least one first fin on a first surface and a second surface which is 
flat; 
a second heat conductive thermal device having a plurality of second fins; 
said at least one first fin being interspersed with said second fins; 
wherein at least one of said first and second fins is of a thermally 
conductive, flexible material so that a gap otherwise existing between 
said interspersed fins is substantially eliminated and wherein at least a 
portion of said first and second fins are biased against one another. 
Preferably, there are a plurality of said first fins.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the Figures in more detail, and particularly referring to FIG. 
1, there is shown an exploded view illustrating the overall mechanical 
assembly of the specific elements of an apparatus, more specifically, a 
high conduction flexible fin cooling module, generally indicated by 10, 
built in accordance with the present invention for removing heat from heat 
generating devices such as semiconductor chips. In FIG. 1, a chip 12 that 
must be maintained below a specific temperature is mounted on a substrate 
14. Preferably, the chips are mounted to substrate 14 by solder balls 
(also known as controlled collapse chip connections or C-4s as disclosed 
in U.S. Pat. No. 3,495,133, the disclosure of which is incorporated by 
reference herein) in a face down orientation. Substrate 14 sits in frame 
22. 
The substrate 14 is preferably a multilayer ceramic (MLC) substrate. The 
substrate may comprise ceramic and/or glass materials. Some of the more 
common materials for the substrate are alumina, cordierite glass-ceramic, 
mullite and borosilicate glasses. It should be understood that the present 
invention is not dependent on the substrate material per se and so would 
be expected to work well with a variety of substrates. 
A finned internal thermal device insert 16 having at least one first fin 17 
on a rigid base is positioned over each chip 12 and is able to move 
laterally in a plane parallel to the chip. Preferably, there will be a 
plurality of first fins 17. Since there are normally a plurality of chips 
in today's high performance modules, there will be a plurality of internal 
thermal device inserts so that each chip is matched with an insert. Second 
thermal device 18 has a plurality of second fins 20 which intermesh with 
the first fins 17 of the internal thermal device insert 16. Second thermal 
device 18 is preferably a cooling hat and will be referred to as such 
hereafter. Upon assembly of the module 10, cooling hat 18 is connected to 
frame 22 by suitable fastening means. Cooling hat 18 may be connected to, 
or be an integral part of, a cold plate (not shown) which provides a 
cooling fluid for dissipating heat from the cooling hat. Alternatively, 
cooling hat 18 may be provided with air cooling fins in the event that 
liquid cooling of the cooling hat is not required. 
The underside of cooling hat 18 is shown more clearly in FIG. 2. As can be 
seen, second fins 20 have been positioned in the cooling hat and are now 
ready for mating with the finned thermal device inserts 16. Second fins 20 
may be retained in the cooling hat 18 by, for example, soldering them in 
fixed relation to the hat. 
An important feature of the present invention is that at least one of the 
first 17 and second 20 fins is a thermally conductive, flexible material 
so that a gap otherwise or normally existing between the interspersed 
sometimes also called intermeshed or interdigitated) fins is substantially 
eliminated. Further, at least a portion and usually all of the first and 
second fins are biased against one another. As will become more apparent 
hereafter, these important improvements lead to a marked decrease in the 
thermal resistance of the cooling apparatus over previous high conduction 
cooling modules. 
While at least one of the first 17 and second 20 fins is a flexible 
material, it is contemplated by the present invention that both of the 
fins may be flexible in nature. If only one of the fins is flexible, then 
the other fin--whether it be first fin 17 or second fin 20--is 
substantially rigid. 
The concept of being "flexible" is difficult to define with precision. The 
flexible fins should be resilient and, at the very least, be capable of 
being bent or flexed without undue difficulty when the first and second 
fins are mated together. The choice of material for the flexible fin is 
not restrictive but should include those materials having good thermal 
conductivity such as copper and beryllium copper. The flexible fins may 
also have been treated to have a spring temper to increase their 
elasticity. 
Referring again to FIG. 1, the module 10 may further comprise a biasing 
means 24 located between the fins of the thermal device insert or the 
cooling hat. The biasing means 24 exerts a biasing force between the 
thermal device insert and the cooling hat. The general concept of this 
particular biasing means has been previously described in great detail in 
the Horvath et al. patent application, mentioned above. Suffice it to say 
here that the biasing means 24 exerts an adequate biasing force to urge 
the base of the thermal device insert toward the chip while not applying 
excessive forces that may destroy chip circuitry or cause excess fatigue 
or damage to the solder ball connections. The biasing means is 
advantageous in that it accommodates height variations among the different 
chips. 
It is most preferred that the module 10 contain the biasing means 24. It is 
also preferred that the module contain a compliant thermally conductive 
medium to aid in the conduction of the heat from the chip to the cooling 
hat. The preferred thermally conductive medium is a synthetic oil such as 
poly(alphaolefin) oil. 
Referring now to FIGS. 4 to 6, the cooperation between all the components 
of the present invention can be seen more clearly. Thermal device insert 
16 comprises a base 70 having a plurality of first fins 17 on a first 
surface 72 of the base 70. A second, opposite, surface 74 of the base is 
flat and is adapted for contacting a chip 12. The number of first fins may 
vary but it is preferable that there be five, and most preferably, six 
fins for a 6.5 mm square chip. Of course, the number of fins will vary 
with the size of the chip, the larger chips having the larger number of 
fins. As shown in these Figures, the first fins 17 are substantially rigid 
and the second fins 20 are the flexible fins. The biasing means 24 resides 
in the channels 26 formed between the ends 30 of the fins 20 and insert 16 
or channels 28 formed between the ends 31 of the fins 17 and cooling hat 
18. For purposes of the present invention, it is preferred that the 
biasing means 24 resides in channels 28 as shown in FIGS. 4 to 6. 
When rigid first fins 17 of the insert are interspersed within flexible 
second fins 20, the flexible fins firmly contact the rigid fins so that 
any gap that might otherwise exist between the interspersed fins is 
substantially eliminated. This is for the ideal case when there is no chip 
tilt. On those occasions when there is chip tilt, the flexible and rigid 
fins will not be parallel to each other but, rather, will be at some 
angle. In this case, the nature of the flexible fins allows the flexible 
fins to bias against the rigid fins to thereby maintain contact between 
the flexible fins and the rigid fins. The flexible fins flex to 
accommodate fin misalignment and chip tilt. Thus, the location of the 
lines of contact between the flexible fins and rigid fins is not fixed. In 
either case, a gap that might otherwise exist between the interspersed 
fins is, for all intents and purposes, eliminated. 
In the most preferred embodiment, when biasing means 24 is present, the 
biasing means will reside in channels 28. The biasing means 24 urges the 
thermal device insert toward the chip to apply a desired pressure against 
the chip, thereby assuring good thermal contact with the chip. 
When the first and second fins are interspersed with each other, the 
flexible fins exert a force normal to the rigid fins. Simultaneously, the 
biasing means exerts a biasing force to urge the base of the thermal 
device insert toward the chip. It should be understood that the respective 
forces of the biasing means and flexible fins should be balanced such that 
the force exerted by the flexible fins is sufficient to firmly contact the 
rigid fins but not be so robust as to defeat the function of the biasing 
means. 
Referring to FIG. 3, the biasing means 24 is shown in greater detail. It is 
possible to make the biasing means separable so that each thermal device 
insert will have its own biasing means, separate and apart from every 
other biasing means. It has been found preferable, however, to make the 
biasing means so that a plurality of individual biasing means are 
connected together. For example, the biasing means 24 shown in FIGS. 1 and 
3 represents all the individual biasing means connected together for the 
module 10. 
The biasing means 24 has cantilever arms 32 which reside in channels 28. 
The cantilever arms 32 urge the thermal device inserts into contact with 
the chips. Individual biasing means are connected by longitudinal supports 
34 which also reside within channels 28. If it were desirable to have more 
than one row of biasing means or more than one cantilever arm per chip 
site, then crosspiece 36 is necessary to connect longitudinal supports 34. 
Crosspieces 36 reside within channels 40 of the flexible second fins 20. 
A further aspect of biasing means 24 is retaining means 38 which maintains 
the thermal device inserts in their respective predetermined locations. 
When a plurality of the thermal device inserts 16 are placed within 
flexible second fins 20, the thermal device inserts must be properly 
located over the chips 12. Subsequently, the location of thermal device 
inserts 16 must be maintained. In the present invention, this is not as 
much a problem as was previously the case since the flexible fins securely 
engage the rigid fins. Nevertheless, it is desirable to have means to 
prevent the thermal device inserts from shifting their respective 
positions during shipment of the module, for example. The arms of 
retaining means 38 act in such a manner to prevent the thermal device 
inserts from shifting. The retaining means 38 also resides in channels 40 
of flexible second fins 20. 
Biasing means 24 may be fabricated by a number of manufacturing methods. A 
method found advantageous by the present inventors is to take a thin sheet 
of stainless steel or other suitable material and then to etch the desired 
pattern. The remaining material may then be bent to form the necessary 
cantilever arms, retaining means, etc. While stainless steel is the 
preferred material, a zirconium-copper alloy may also be used for the 
biasing means. Of course, the biasing means may be manufactured by methods 
other than the one just described. 
An accomplishment of the present invention is eliminating the gap between 
the interspersed fins of the thermal device insert and the cooling hat. It 
has been found that this gap is a significant contributing factor to the 
overall thermal resistance of the high conduction cooling module. 
Accordingly, the thermal resistance of the module can be decreased by 
substantially eliminating the gap. This remains the case even though the 
thermal resistance of the flexible fins is not as low as for rigid fins. 
The thickness of each of the rigid fins may be increased somewhat so that 
the thickness of each of the rigid fins is greater than the spacing 
between each of the adjacent rigid fins. The increased thickness of the 
rigid fins further helps to dissipate heat in the present invention. 
A preferred embodiment of the flexible second fin 20 is illustrated in 
FIGS. 5 and 6. As shown therein, the flexible fins are generally U-shaped 
in cross-section with the base of the U attached to the cooling hat at 42. 
The longitudinal dimension of the flexible fins approximates that of the 
thermal device insert. When the first and second fins are interspersed, 
the first rigid fin 17 is inserted between the legs 44 of second flexible 
fin 20. Channels 26, 28 remain available for the placement of the biasing 
means 24, which would of course have been inserted prior to the 
interspersing of the first and second fins. For ease of assembly, the ends 
30 of each of the legs 44 are bent outwardly. In FIG. 5, one of the 
flexible fins 20 is removed so that the cantilever arm 32 of biasing means 
24 can be seen. 
The height of the fins may be varied if desired, consistent with thermal 
design principles. The optimal fin height may be determined in the 
following manner. The total thermal resistance of the fin arrangement is 
the sum of the thermal resistance of the average gap between the fins and 
the thermal resistances (summed) of the first and second metal fins. The 
optimal thermal resistance is obtained when the thermal resistance of the 
average gap approximately equals the summed thermal resistances of the 
metal fins. For example, taller fins give a relatively smaller average gap 
thermal resistance (large area) but a larger summed metal thermal 
resistance. Conversely, shorter fins have a relatively larger average gap 
thermal resistance (smaller area) but a smaller summed metal thermal 
resistance. The optimal design will usually lie somewhere between these 
two extremes. 
The present invention has thus far been described in general terms in that 
at least one of the first and second fins is flexible. More specifically, 
one of the first and second fins is flexible and the other is 
substantially rigid. In the preferred embodiment just discussed, the first 
fins (of the thermal device insert) are substantially rigid while the 
second fins (of the cooling hat) are flexible. Other embodiments of the 
invention will now be discussed. 
Referring now to FIG. 7, there is shown an embodiment of the invention 
where both the first and second fins are flexible. As in FIG. 6, second 
flexible fin 20 is generally U-shaped. Now, however, first fin 17 is also 
generally U-shaped and is attached to the rigid base of the thermal device 
insert at 46. 
It is also possible that at least one of the first and second fins could be 
tapered. Thus, in FIG. 8, first fin 17 is rigid and tapered. This 
embodiment ensures that the lines of contact between the flexible fins and 
the rigid fins are always below the tops of the fins which further ensures 
that the springs will not be forced open in case of misalignment between 
the flexible fins and the rigid fins. The same result can be achieved if 
the rigid fins are straight and the flexible fins are tapered. This latter 
embodiment of the invention is not shown in the Figures. 
In FIG. 9, short flexible fins 20 contact short rigid fins 17 at the bends 
in the springs. In this case, the locations of the lines of contact are 
nearly independent of chip tilt. The spring force of the flexible fins may 
be made higher to ensure zero gap along the lines of contact. Because of 
the low thermal resistance through the contacts, long engagement length is 
not required. 
In another embodiment of the invention, as shown in FIG. 10, the legs 44 of 
second flexible fins 20 are interspersed between each of the rigid first 
fins 17. Note that the ends 30 of the flexible fins are preferably turned 
inwardly to assist in the assembly of the first and second fins. 
It may be desirable to make the second flexible fins out of a soft heat 
conductive material such as copper which has limited elasticity (i.e., low 
elastic limit). In this design, separate biasing means, for example 
springs 48, are inserted between the legs of the second flexible fins 20. 
This embodiment is illustrated in FIG. 11. 
It is also contemplated within the scope of the invention that the second 
flexible fins 20 may be seated within grooves or slots 50 within the 
cooling hat 18. This embodiment, illustrated in FIG. 12, provides an 
additional heat flow path through the otherwise non-overlapped portions of 
the flexible fins. 
In FIG. 13, the cooling hat 18 further comprises grooves or slots 52 
between each of the flexible fins 20. When the first fins 17 are 
interspersed with the flexible fins 20, the ends 31 of the first fins 17 
are at least partially received in these grooves or slots 52. In this way, 
short flexible fins may be mated with longer first fins. 
Generally speaking, however, it is preferred that the first and second fins 
be of equal dimensions. 
In the previous embodiments, the first fin 17 has been rigid and the second 
fin 20 flexible or both fins 17, 20 were flexible. The previously 
described embodiments apply equally as well to those designs where the 
first fins 17 are flexible and the second fins 20 are rigid. 
Referring now to FIGS. 14, an embodiment of the invention is shown wherein 
the thermal device insert 16 has a circular cross-section, as can be seen 
in FIG. 14B. In this embodiment, flexible fins 17 are inserted within 
rigid fins 20 and each thermal device insert 16 may have its own biasing 
means 24. 
There may, in fact, be only one fin comprising the thermal device insert. 
As can be seen in FIG. 15A, thermal device insert 16 has a single rigid 
fin 17 which intermeshes with flexible fins 20. This thermal device insert 
16 may be also circular in cross-section and have its own biasing means 
24. As can be seen in FIG. 15B, flexible fins 20 are also circular and are 
preferably segmented, i.e., having gaps 88. 
In FIG. 16A, rigid fins 17 mesh with flexible fins 20. In this embodiment, 
however, outer flexible fins 80 contact the outer surface 85 of rigid fins 
17 while inner flexible fins 82 protrude into an inner cavity 84 of the 
thermal device insert 16 to contact an opposite surface 86 of rigid fins 
17. As can be seen from FIG. 16B, the rigid fins 17 and flexible fins 20 
are circular in cross-section. Additionally, flexible fins 20 preferably 
are segmented with gaps 90. 
In the embodiments of FIGS. 17 to 19, the flexible fin is axially split. 
For purposes of illustration and not of limitation, the flexible fins in 
these embodiments are the first fins 17 and the second fins 20 are rigid. 
The relative positions of the first and second fins could just as easily 
have been reversed. 
Referring now to FIG. 17, first fins 17 have been axially split 54 instead 
of being U-shaped in order to be flexible. Second fins 20 are rigid. In 
FIG. 18, the rigid fins are tapered. 
In FIG. 19, the first flexible fins 17 are axially split but are also 
heavier in cross-section with decreased flexibility. It is preferred that 
the central portion 58 of the axially split fins have a large radius as 
shown. To increase the flexibility somewhat, the axially split fins are 
notched 60 at their base. The outer fins 56 of the second fins (which are 
rigid) may also be made heavier in cross-section. 
FIG. 20 illustrates a final embodiment of the present invention. The 
thermal device insert has first flexible fins 17 which engage rigid second 
fins 20. The rigid second fins also have an enlarged tapered base portion 
62 which engages the tips 64 of the flexible fins. In FIG. 20A, rigid fins 
20 are about to enter flexible fins 17. Thereafter, the flexible fins 17 
are spread apart beyond their elastic limit, as shown in FIG. 20B, and 
then withdrawn back to their operating location, as shown in FIG. 20C. 
This results in controlled spring force and location. 
Other advantages of the invention will become more apparent after referring 
to the following examples. 
EXAMPLES 
In the following comparative examples, the high conduction cooling 
apparatus of Horvath et al. was compared to the high conduction flexible 
fin cooling apparatus of the present invention. 
The dimensions of the critical components of the present invention are 
determined by the size and power dissipation of the chips to be cooled. 
That is, in order to dissipate heat from a 25 watt chip (in the case of 
the Horvath et al. apparatus) or a 35 watt chip (in the case of the 
present invention) of chip size 6.5.times.6.5 mm square in a system 
wherein poly(alphaolefin) oil is used as the compliant thermal medium and 
wherein the finned internal thermal device insert is made of copper, the 
preferred embodiment may be constructed in the following manner. 
The preferred insert of the present invention has 6 rigid fins and each fin 
has a width of 1 mm. The width of the flexible fins of the cooling hat are 
approximately 0.15 mm. For the Horvath et al. apparatus, there are 5 rigid 
fins and each fin has a width of 0.8 mm. The fins of the cooling hat are 
also rigid and have a width of 0.8 mm. 
For each apparatus, the rigid base of the insert is about 9.1 mm square and 
about 1.3 mm thick. The vertical height of each fin from the top of the 
rigid base is approximately 5.8 mm. The length of the fins in the has is 
about 5.8 mm. The overlapping length of corresponding fins is about 4.8 
mm. 
The average width of the oil filled gap between corresponding fins is 
approximately, 0.035 mm for the Horvath et al. apparatus and approximately 
0.009 mm for the present invention. 
A double cantilever spring was used for each apparatus; however, the spring 
for the Horvath et al. apparatus was made from a zirconium/copper alloy 
while the spring for the present invention was made from stainless steel. 
To accommodate manufacturing tolerances, there was about a 0.8 mm space 
between the top of the fins and the hat and a 0.8 mm space between the 
bottom of the fins and the rigid base of the insert. 
For the above described Horvath et al. apparatus, the total thermal 
resistance was approximately 1.1.degree. to 1.4.degree. C. per watt. This 
thermal resistance measured between the chip and the cooling hat provided 
for the required dissipation of approximately 25 watts per 6.5 mm square 
chip in a high conduction cooling system wherein the water or other 
thermally conductive fluid cannot be directly incorporated into the chip 
compartment. 
In comparison, the total thermal resistance for the present invention was 
about 0.8.degree. C. per watt which was sufficient to dissipate 
approximately 35 watts per 6.5 mm square chip in a similar high conduction 
cooling system. 
In either apparatus, chip tilt and height variations are easily 
accommodated. The double cantilever spring retained the finned internal 
thermal device insert against the chip surface with at least 120 grams of 
force, but less than approximately 500 grams of force to prevent damage 
to the solder ball joints or chips circuitry. In addition, the temperature 
over the surface of the chip was uniform and maintained within acceptable 
limits. No debris was found at the interface, as all was embedded into the 
soft metal face of the finned internal thermal device insert. 
The results are summarized in Table I below. 
TABLE I 
______________________________________ 
Present Horvath 
Invention et al 
mm. mm. 
______________________________________ 
Oil gap .009 .036 
Cooling hat fin .15 .8 
thickness 
Insert slot width 
.51 .89 
Insert fin width 
1 .8 
Number of fins 6 5 
Overlap 4.8 4.8 
(engagement length) 
Tilt accommodation 
Flexing Fins 
Fin gaps 
Thermal resistance 
.14.degree. C./w 
.56.degree. C./w 
of Gap (Rgap) 
Thermal Resistance 
.8.degree. C./w 
1.1-1.4.degree. C./w 
Chip & Cold Plate 
(Rint) 
Pchip (max) 35 watts 25 watts 
______________________________________ 
It is believed that with a larger 10 mm square chip, these results can be 
improved to Rint=0.5.degree. C./watt and Pchip(max)=60 watts with the 
present invention. 
It will be apparent to those skilled in the art that having regard to this 
disclosure that other modifications of this invention beyond those 
embodiments specifically described here may be made without departing from 
the spirit of the invention. Accordingly, such modifications are 
considered within the scope of the invention as limited solely by the 
appended claims.