Heat exchanger for integrated circuit packages

The present disclosure describes a heat exchange device for attachment to the external surface of a package containing an integrated circuit chip or die. The device has particular application in high density electronic packaging configurations, where space limitations severely curtail the volume which can be occupied thereby. The structure of the present device is such that both the effective cooling area per given volume and the heat transfer coefficient are maximized. Basically, the device is an integral structure comprised of a generally helical wire form affixed to a metallic frame-like member. The wire form provides a plurality of parallel closely spaced-apart cylindrical sections capable of being disposed in an air stream for dissipating the heat generated in the integrated circuit package to which the device is attached.

BACKGROUND OF THE INVENTION 
An assential requirement for the operation of integrated circuits is the 
transfer of heat generated by the integrated circuit chip from the package 
itself to the external environment. The problem of heat dissipation is 
especially acute in high density packaging applications where the volume 
allotment for heat exchange media is extremely limited. 
Commonly used heat exchange or heat sink devices for integrated circuit 
packages result from extrusions, stampings, and machined parts formed in a 
variety of shapes and configurations. However, because of size and volume 
constraints, none of these manufacturing methods yield devices which offer 
maximum effective cooling area for a given volume. The latter criterion is 
a prime factor in overall heat exchanger performance. Related to the 
effective cooling area of the device is its heat transfer coefficient 
factor. Here again, the above-mentioned devices do not maximize this 
characteristic. It is apparent that the heat that is transferred from the 
package to the ambient must overcome the thermal resistance of the heat 
exchanger itself. The largest component of the total resistance offered by 
the heat exchange device is designated film resistance and is inversely 
proportional to the surface area of the device. Stated another way, film 
resistance is the reciprocal of the product of the effective surface area 
and the convective heat transfer coefficient. Maximizing the latter 
factors, reduces the film resistance of the heat exchanger. 
The present device accomplishes the foregoing with a simple, economical, 
volume effective structure. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a heat exchange device is 
provided for attachment to an integrated circuit chip carrier or package, 
for dissipating the heat generated by the chip during circuit operation. 
The heat exchange device of the present invention is comprised of two 
basic parts, namely, a wire form and a metallic frame-like retainer plate, 
which parts are assembled and bonded together to form an integral unit. 
In an actual operative embodiment of the device, the wire form was 
constructed from a continuous length of wire formed into a helical coil 
with spaced-apart wraps or turns. Each turn resembles an open "T", with an 
upper turn portion joined by a pair of legs to a comparatively shorter 
lower turn portion, corresponding respectively to the horizontal top, 
vertical sides and horizontal base of the "T". 
The retainer plate is a generally rectangular frame-like member having a 
plurality of spaced-apart cutouts or notches along the edges of two 
opposed sides of its central opening. The perimeter of the plate defines 
the approximate cross section of the volume allotted to the heat 
exchanger. 
In assembly of the device, the wire form is inserted into the opening of 
the retainer plate. The aforementioned upper turn portions remain upright 
and rest upon the surface of the retainer plate, while the leg portions of 
the turns are accommodated by the cutouts. The lower turn portions serve 
as connecting members, joining a leg of one turn with the opposite leg of 
the next succeeding turn. The lower turn portions therefore exhibit a 
pitched configuration relative to the upper turn portions which are 
oriented in rectangular fashion in conformance with the shape of the 
retainer plate. The plate provides both the desired spacing for the coil 
turns and increased rigidity. The wire form and the retainer plate are 
then bonded together by any suitable method, such as reflow soldering, dip 
brazing or spot welding. As will be described in detail hereinafter, the 
retainer plate also serves to enhance the thermal effect of the wire form. 
The heat exchanger of the present invention offers significant advantages 
over commonly employed heat exchange media. Thus, its low profile and 
minimal size make it useful in high density packaging applications. It 
provides maximum surface area and convective heat transfer coefficient for 
a given volume. Moreover, it provides minimum restriction to air flow in a 
forced air system, and is bidirectional with respect thereto. Also, it is 
easily attached to the integrated circuit package and imparts minimal 
thermal stress to the latter as a result of processing and other thermal 
excursions. 
Other features and advantages of the heat exchanger of the present 
invention will become more apparent in the detailed description which 
follows:

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Because of the close relationship of the figures, and the relative 
simplicity of the heat exchange device 10 of the present invention, 
specific reference should be made to FIG. 1, along with concurrent general 
reference to FIGS. 2 and 3 in the following description. 
The device 10 is comprised of two parts, a wire form 12 and a retainer 
plate 14. In an actual operative embodiment, the wire form 12 was 
constructed of a continuous length of wire shaped into a coil having a 
plurality of spaced-apart turns. As seen particularly in FIG. 2, each turn 
of the coil exhibits a low-profile, open "T" configuration, wherein an 
upper turn portion 12a is joined by a pair of legs 12b to a comparatively 
shorter length lower turn portion 12c. 
The retainer plate 14 is a rectangular, metallic, frame-like member having 
a plurality of homologous spaced-apart cutouts 16 along the respective 
edges of two opposed sides of its central opening 18. The perimeter of 
plate 14 defines the approximate cross section of the volume which may be 
occupied by the heat exchanger. 
As best seen in FIGS. 2 and 3, the heat exchange device 10 is assembled to 
the retainer plate 14 by maintaining the longitudinal axis of its wire 
form 12 parallel to the planar surface of plate 14 and inserting the lower 
turn portions 12c through the opening 18 of the latter. The upper turn 
portions 12a are now supported by the retainer plate 14 while the legs 12b 
are disposed in cutouts 16. It is apparent that the cutouts 16 help to 
maintain the spacing of the coils, one from the other. As seen 
particularly in FIGS. 1 and 3, the lower turn portions 12c serve as 
connecting members, each one joining a leg of one turn with the opposite 
leg of the next succeeding turn. Accordingly, the lower turn portions 12c 
exhibit a pitched configuration relative to the upper turn portions 12a. 
As seen in FIG. 2, the respective outermost surfaces of both the upper and 
lower turn portions 12a and 12c, are flattened in a planar (as opposed to 
an arcuate) shape. Accordingly, the last mentioned surfaces lie in 
respective planes parallel to that of the retainer plate 14. The wire form 
12 and the retainer plate 14 are then bonded together by any suitable 
method, such as reflow soldering, dip brazing, or spot welding. The 
retainer plate 14 offers increased rigidity to the wire form 12. 
FIG. 2 illustrates in simplified fashion, the heat exchange device 10 of 
the present invention attached to an integrated circuit package 20. The 
latter, commonly formed of ceramic, includes a cavity 22 within which the 
chip 24 is mounted. A metallized element 26 is shown bonded to the outer 
surface of the package 20. In practice the element 26 may be inlaid in the 
ceramic surface. In either case, the element 26 may extend across the 
entire surface of the package, or may be localized in the vicinity of the 
chip 24. 
The heat exchange device 10 is attached to the metallized element 26. This 
is accomplished by bonding the lower turn portions 12c of the wire form 12 
to the element 26 by soldering or the use of heat conductive adhesives. 
The heat generated by the chip 24 is conducted via the lower turn portions 
12c and the legs 12b of the wire form 12 to the retainer plate 14 which 
tends to distribute the heat to all of the upper turn portions 12a, 
thereby improving the bulk conductions of the device 10. It has been found 
that while the heat exchange device 10 may interface with a large 
metallization field, it induces minimal thernal stress on the package as a 
result of processing and temperature excursions. 
The heat exchange device 10 of the present invention is especially suitable 
for forced air cooling--the upper turn portions 12a of the wire form 12 
offering minimal resistance to air flow. It should be noted that as air 
passes over a heat exchanger with substantially flat surfaces, such as the 
known devices which are extruded, stamped or machined, a boundary layer 
adjacent the heat exchange surface is produced which affects the degree of 
heat dissipation. In contrast, the upper turn portions 12a of the wire 
form 12 of the present device appear as a multiplicity of parallel 
spaced-apart cylindrical members. Although the present device is 
bidirectional with respect to the direction of air flow, optimum results 
occur when the air stream is parallel to the coil axis of the wire form 
12. This is true because air flow directed across members of circular 
cross section, cause a turbulent effect on the back side of each of the 
members, thereby improving the conditions for heat transfer. In effect, 
the turbulence breaks up the boundary layer effect noted hereinbefore, and 
increases the convective heat transfer coefficient. 
In conclusion, it is submitted that the heat exchanger disclosed herein 
offers a low-cost, simple, highly efficient means of heat dissipation in a 
high density integrated circuit package configuration. The inventive 
concepts described herein are generic to various applications. In an 
actual operative situation, copper wire having a diameter of 0.042 inches 
was used for the wire form, while the copper retainer plate was 0.80 
inches square and had a thickness of 0.032 inches. The overall height of 
the heat exchanger was 0.27 inches. It should be understood that in other 
applications, changes and modifications of the foregoing parameters may be 
needed to suit particular requirements. Such variations are within the 
skill of the designer, and do not depart from the true scope and spirit of 
the invention and are intended to be covered by the following claims: