U.S. patent number 3,993,123 [Application Number 05/626,399] was granted by the patent office on 1976-11-23 for gas encapsulated cooling module.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Richard C. Chu, Omkarnath R. Gupta, Un-Pah Hwang, Robert E. Simons.
United States Patent |
3,993,123 |
Chu , et al. |
November 23, 1976 |
Gas encapsulated cooling module
Abstract
A gas encapsulated cooling unit is provided for one or more heat
generating components mounted on a substrate. A heat conductive cap
is sealed to the substrate enclosing the heat generating
components. The wall of the cap opposite the substrate contains
elongated openings therein extending towards the heat generating
components and on the same centers with respect thereto. A
resilient member is located in the cap in communion with the inner
end of the openings. A thermal conductive element is located in
each of the openings forming a small peripheral gap between each
opening wall and the associated thermal conductive element. The
resilient member urges the thermal conductive elements into
pressure contact with the heat generating components. A thermal
conductive inert gas is located within the cap filling the
peripheral gaps and the interfaces between the heat generating
elements and the thermal conductive elements. The heat is removed
from the cap by external heat removal means.
Inventors: |
Chu; Richard C. (Poughkeepsie,
NY), Gupta; Omkarnath R. (Poughkeepsie, NY), Hwang;
Un-Pah (Poughkeepsie, NY), Simons; Robert E.
(Poughkeepsie, NY) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
24510237 |
Appl.
No.: |
05/626,399 |
Filed: |
October 28, 1975 |
Current U.S.
Class: |
165/80.3;
165/80.4; 257/697; 257/719; 257/E23.11; 165/104.33; 257/714;
257/720; 361/703; 257/E23.094; 257/E23.095; 257/E23.098 |
Current CPC
Class: |
H01L
23/373 (20130101); H01L 23/4338 (20130101); H01L
23/44 (20130101); H01L 23/473 (20130101); H01L
2924/0002 (20130101); H01L 2924/0002 (20130101); H01L
2924/00 (20130101) |
Current International
Class: |
H01L
23/473 (20060101); H01L 23/373 (20060101); H01L
23/34 (20060101); H01L 23/44 (20060101); H01L
23/433 (20060101); H05K 7/20 (20060101); H01L
023/44 () |
Field of
Search: |
;165/80,105 ;357/82
;317/100 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Cohan; Alan
Attorney, Agent or Firm: Sweeney, Jr.; Harold H.
Claims
What is claimed is:
1. A gas encapsulated cooling module for heat generating elements
comprising:
a substrate;
one or more heat generating components mounted on said
substrate;
a heat conductive cap sealed to said substrate enclosing said one
or more heat generating components;
the wall of said cap opposite the substrate containing elongated
openings therein extending toward said heat generating components
and on the same centers with respect thereto,
a resilient member located in said cap in communion with the inner
end of said openings;
one or more thermal conductive elements each located in one of said
openings forming a small peripheral gap between the opening wall
and said associated thermal conductive element, said resilient
member urging said thermal conductive element into contact with one
of said heat generating components forming a heat transfer
interface therewith;
a thermal conductive inert gas located within said cap filling the
peripheral gaps and said heat generating element conductive element
interface;
heat removal means associate with said cap for externally removing
the heat generated by said heat generating means from said cap.
2. A gas encapsulated cooling module according to claim 1, wherein
said one or more heat generating devices are electronic chips and
said thermal conductive inert gas is helium.
3. A gas encapsulated cooling module according to claim 1, wherein
said cap is made of a good thermal conductive material for acting
as a good thermal path for the heat flow thereto by conduction
through said gas in said peripheral gap from said thermal
conductive elements and by convection via said gas from said heat
generating devices.
4. A gas encapsulated cooling module according to claim 2, wherein
said helium gas pressure is obtained from a helium capsule having a
given rate of gas leakage located within said cap to provide a
continuous positive pressure within said cap preventing the
entrance of ambient air.
5. A gas encapsulated cooling module according to claim 1, wherein
said heat removal means is a coldplate having a wall of said cap
forming a wall of said coldplate, said wall having an inward
extension of high thermal conductivity material surrounding the
peripheral surface of said heat conductive elements forming said
small peripheral gap over the entire peripheral area thereof which
contains said gas to give a good heat transfer path to said heat
removal means.
6. A gas encapsulated cooling module according to claim 1, wherein
said heat removal means comprises a plurality of cooling fins
extending from the outer wall of said cap, said wall having an
inward extension of high thermal conductivity material surrounding
the side surfaces of said heat conductive elements forming a gap
therebetween containing said gas to give a good heat transfer path
from said heat conductive elements to said cap, and cooling fins
extending therefrom which are adapted for heat removal by forced
air.
7. A gas encapsulated cooling module according to claim 1, wherein
said resilient member comprises a plurality of springs, one
compressed between each of said heat conductive elements and said
cap to maintain said conductive elements pressed against respective
heat generating devices to form good heat conductive gas filled
interfaces therebetween.
8. A gas encapsulated cooling module according to claim 1, wherein
said resilient member is variable as a function of temperature to
provide self-regulation of the pressure exerted by said resilient
member.
9. A gas encapsulated cooling module according to claim 8, wherein
said resilient member comprises an expandable member containing a
binary mixture of fluorocarbon liquids which changes phase at a
predetermined temperature controlled by the mixing ratio to provide
self-regulation of interface pressure in accordance with
temperature.
10. A gas encapsulated cooling module according to claim 9, wherein
said expandable member is an elastic tube located in a channel and
arranged in a continuous manner to be across the top end of each of
said heat conductive elements so as to impart pressure through
expansion to said heat conductive elements as the temperature of
the fluorocarbon liquid rises in response to an accumulative
increase in heat generating device temperature.
Description
STATEMENT OF THE INVENTION
This invention relates to conduction cooling of small heat
generating electronic devices and, more particularly, to the
cooling by conduction of miniaturized electronic devices in an
encapsulated, inert, high thermal conductivity gaseous
atmosphere.
BACKGROUND OF THE INVENTION
With the miniaturized capabilities afforded by the discovery of
solid state electronics, various improved means of dissipating the
heat generated by solid state components have been investigated.
The standard forced air convection means appears to have reached
its's limit of practicality in that the amount of air that is
required to provide sufficient cooling for the limited heat
dissipating surfaces introduces a noise problem, and without some
auxiliary techniques cannot maintain each of a large number of
components within it's critical, narrow operating temperature
range. Accordingly, especially in connection with large scale
computer systems, various combinations of air-liquid cooling
systems have been devised. One of the more recent systems
investigated has been the immersion cooling system, wherein the
array of components to be cooled is immersed in a tank of cooling
liquid. The liquids used are the new fluorocarbon liquids which
have a low-boiling point. These liquids are dielectric and give
rise to various types of boiling at relatively low temperatures. In
view of the problems encountered in servicing and packaging
components which are cooled using this immersion technique, an
encapsulated cooling technique was devised which includes the same
dielectric material encapsulated separately for each module. U.S.
Pat. No. 3,741,292, issued June 26, 1973 shows an example of a
module having the heat generating components located thereon
surrounded by a low boiling point dielectric liquid which is
encapsulated thereto. A vapor space is located above the liquid
level, which is filled with internal fins extending into the
container serving as a condenser for the dielectric liquid vapors.
External fins extend outward from the container and serve as an air
cooled sink for the internal fins condenser. However, this type of
a modular liquid encapsulated cooling device must meet certain
inflexible requirements. For instance, it requires coolant of
extremely high purity and free of any contaminants. It's operation
is sensitive to all the variables which govern the basic process of
nucleate boiling and vapor condensation. Furthermore, the concept
is not readily adaptable to small scale applications such as a
single heat generating component.
Accordingly, it is the main object of the present invention to
provide an encapsulated cooling unit which utilizes inert gas
having good thermal conductivity as the encapsulated medium in
combination with a conductive heat transfer arrangement.
It is another object of the present invention to provide
encapsulated inert gas having good thermal conductivity and having
a low molecular weight so that it fills the heat transfer
interfaces thereby providing a low thermal resistance path.
It is a further object of the present invention to provide an
encapsulated inert gas with good thermal conductivity and a heat
conducting element combination for cooling, in which the element is
urged against the heat generating component to decrease the thermal
resistance of the interface.
It is a further object of the present invention to provide an
encapsulated inert gas having good thermal conductivity and a heat
conductive element combination in which the heat transfer is
automatically regulated as a function of temperature.
SUMMARY OF THE INVENTION
An encapsulated cooling unit is provided for one or more heat
generating devices to be cooled which are mounted on a substrate. A
cap is sealed to the substrate enclosing the heat generating
devices to be cooled. An inert gas and good thermal conductive
elements are contained within the sealed volume between the cap and
the substrate. Each of the heat conductive elements are urged
against respective ones of the heat generating devices forming a
smallest gas gap to provide lowest thermal resistance. A heat sink
associated with the cap receives the heat from the heat conductive
elements through an annular gap which likewise contains the inert
gas.
The foregoing and other objects, features and advantages of the
invention will be apparent from the following more particular
description of a preferred embodiment of the invention, as
illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical cross-sectional side view of a module showing
the elements within the sealed volume between the cap and the
substrate.
FIG. 2 is a vertical cross-sectional side view of a module showing
fins extending therefrom suitable for air cooling.
FIG. 3 is a cross-sectional view taken along the line 3--3 in FIG.
1.
FIG. 4 is an expanded perspective view of part of the inside of the
cap showing the tubular member pressure actuator and one of the
conductive elements.
FIG. 5 is a view taken along line 5--5 of FIG. 1 showing the
serpentine configuration of the thermal pressure actuator.
FIG. 6 is a cross-sectional side view showing a module containing
encapsulated gas and a single thermal conductor arrangement for
cooling a single chip.
FIG. 7 is a view looking along the line 7--7 of FIG. 6 showing the
individual thermal pressure actuator.
FIG. 8 is an expanded cross-sectional view of a part of a module
showing an individual pressure actuator for each thermal conductor
and showing the various thermal resistances in the thermal
path.
FIG. 9 is a plot of the thermal resistance from the chip to the
cooling water of the external heat removal means versus the thermal
conductive stud length for various materials.
DESCRIPTION OF PREFERRED EMBODIMENT
Referring to FIG. 1 there is shown a cross-sectional view of a gas
encapsulated module for providing cooling of the solid state
electronic chips 10 to be cooled. As is well known, the chip
consists of solid state circuits and devices which are densely
packed on each chip. The power consumed in the circuits within the
chip generates heat which must be removed from the chip. Since the
various circuits have different power requirements, and since the
integrated components thereon must be maintained within certain
temperature ranges for reliable operation, the cooling must be of
such character as to maintain the chip temperature within the
required operating range.
The chips 10 are mounted on one side of a substrate 12, generally
made of ceramic, which has pins 14 extending from the other side
thereof. These connecting pins 14 provide for the plugging of the
module into a board (not shown) which may very well carry auxiliary
circuits etc. A container or cap 16 is attached to the substrate 12
by means of a flange 18 which extends from the periphery of the
substrate 12 to the cap 16. The cap 16 is made of a good heat
conductive material such as copper or aluminum. The cap 16 is
sufficiently thick to provide openings 20 therein and a channel 22
therethrough associated with each of the closely spaced openings.
The cap 16 instead of being thick can have extensions therefrom
which extend toward the chip 10 and which has an opening or hole 20
in each extension. The channel 22 in the cap 16 extends over the
openings 20 therein such that a resilient tube 24 mounted in the
channel 22 passes over the end of each of the openings 20. The
tubular member 24 which serves as a pressure actuator is inserted
into the channel 22 in the cap 16 from the outer side before the
conductive elements 26 are inserted into their holes 20, as can be
seen in FIG. 4. This resilient tubular member 24 includes a binary
fluid mixture of fluorocarbons which changes phase at a present
temperature, controlled by the mixing ratio. The expanding fluid
causes the resilient tubular member 24 to expand as a function of
temperature. The openings or holes 20 within the cap member 16 are
accurately sized to receive a thermal conductive element 26, one
end of which abuts the tubular member 24 and the other end of which
abuts the face of the chip 10 forming an interface 28 therebetween.
As can be seen in FIGS. 3 and 4, element 26 is dimensioned such
that a small annular gap 30 exists between it's circumference and
the side walls of the hole 20 in the cap 16. The gap 30 is
sufficiently wide to allow a little play of the element 26 within
the hole 20 so that the element 26 can attain relatively flat
surface engagement with the chip 10. It should also be appreciated
that the thermal conductive element 26 is adaptable to chips 10 of
various heights because of the pressure actuator tubular member
resiliency. Helium gas 32 is introduced into the open space between
the substrate and the cap 16 through the gas fill opening 34 shown
at the top of FIG. 1. Helium gas is utilized for several reasons.
The gas has a low molecular weight and thus easily fills the voids
in the interface 28 between the thermal conductive elements 26 and
the chips 10. Likewise, the helium gas 32 fills the gap 30 between
the periphery of the thermal conductive element 26 and the wall of
the hole 20 thus forming a gaseous thermal conductive interface.
Another feature of the gas is that it is a good thermal conductor
and, therefore, forms an interface having high heat conductivity.
That is, the interfaces formed using helium gas have a relatively
low thermal resistance. Another feature of the gas which is very
important is that it is inert. By inert is meant that the gas is
electrically non-conductive, non-poisonous, non-corrosive,
non-flammable, non-explosive and non-toxic. The gas also has a high
adhesion quality that essentially wets the surface which it is in
contact with. Other low-molecular weight gases such as hydrogen or
carbon dioxide could be used. However, these gases appear to have
undesired properties such as the explosive nature of hydrogen. As
can be seen from FIG. 3, the thermal conductive elements 26 have a
flange like extension 36 at opposite sides thereof but are
otherwise cylindrical in shape. The flange extensions 36 were
included to obtain more surface area on the thermal conductive
element 26 to provide a greater thermal transfer therefrom. These
flanges also serve as keys to properly orient the thermal
conductive elements 26 within the holes 20. The interface 28
between the thermal conductive element 26 and the chip 10 is
actually a pressure interface since the thermal conductive elements
26 are urged against the chips 10 by the resilient tubular member
24 pressing on the other end thereof. FIGS. 1, 2, 6 and 8 show the
interface 28 as a small gap for purposes of illustration. Thus,
this pressure interface 28 containing a thermal conductive inert
gas in the voids provides a low resistance to the heat transfer
and, accordingly, provides a high heat conductive interface. The
gap 30 around the periphery of the thermal conductive element 26
and it's extensions or flanges 36, as previously mentioned, forms a
wider gap with the surrounding walls of the cap 16. Since the gap
30 is wider, even though it is filled with the high thermal
conductive helium gas 32, it has a higher thermal resistance than
is encountered with the interface 28 between the chip and the
thermal conductive element 26. Accordingly, more surface area of
the conductive element 26 is required to transfer the same amount
of heat across the higher thermal resistance gap 30 than is
required to transfer the equal amount of heat across the lower
thermal resistance gap at the pressure interface 28. Thus, the
module must be designed to obtain the required heat transfer rate
to maintain the chip 10 within it's required operating range. The
heat accumulated in the good thermal conductive material cap 16
from each of the thermal conductive elements 26 is transferred to a
coldplate 38 which is attached to the cap 16. As can be seen FIG.
1, the cap 16 surface is relatively flat so that the coldplate 38
can be attached thereto in good thermal conductive relation. The
cap 16 can also serve as the wall of the coldplate. The coldplate
38 has a cooling liquid 40 circulated therethrough which removes
the heat transferred to the coldplate.
The module is not limited to the coldplate type of exterior heat
removal. As shown in FIG. 2, the outer surface of the cap 16 has
fins 42 arranged thereon such that air can be forced thereacross to
remove the heat.
FIG. 8 shows expanded heat path portion of a gas encapsulated
cooling module having cylindrical thermal conductive elements 44.
The various gaps and paths the heat passes through in order to be
removed by the external heat removal means is also shown. The heat
from the chip 46 must overcome the resistance R1 of the gap or
inerface 50 between the chip 46 and the thermal conductive element
44. The thermal conductive element 44 is made of copper or other
good heat conducting materials which results in lower thermal
resistance R2. The gap 52, as mentioned previously, has helium
therein and the thermal resistance R3 must be overcome. The thermal
resistance R4 is calcuated for the material of the cap 48. Thermal
resistance R5 represents the resistance of the interface between
the cap 48 and the coldplate 50, and the thermal resistance R6
represents the resistance from the coldplate 50 to the liquid 54.
The thermal resistance R1 with the helium located in the interface
50 is approximately five times less than the thermal resistance
using air in the interface.
FIG. 4 is an expanded perspective view showing the pressure
actuator tubular member 24 and one of the thermal conductive
elements 26 in place within the channel 22 and hole 20 in the cap
16, respectively.
FIG. 5 shows a view taken along 5--5 of FIG. 1 showing the
serpentine arrangement of the resilient tubular member 24 covering
each of the back ends of the conductive elements 26 to urge them
against their respective chips. It should be appreciated that as
the overall heat generated by the chips rises, the temperature of
the helium gas surrounding the tubular member rises causing the
resilient tubular member 24 which, as previously mentioned,
contains a binary mixture of flurocarbon liquids, to rise in
temperature and expand. Thus, the level of pressure exerted on the
thermal conductive elements 26 will be self-regulated as a function
of temperature, of course, it will be limited by the maximum
temperature.
It should be noted that the operation of the module is independent
of it's orientation. It also works in low gravity or zero gravity
environments such as in space or on the lunar surface.
A single chip, helium encapsulated, conductive cooling unit is
shown in FIGS. 6 and 7. The chip is shown mounted on a substrate 58
which has the pins 60 extending from the opposite side thereof for
plugging the unit onto a board. A cap or container 62 is sealed to
the substrate enclosing the chip 64. The cap 62 has a central
extension 66 which extends from the top of the capy into the
encapsulated area. The extension 66 has a hole therein which
extends from the end of the extension nearest the chip 64 to the
wall of the cap 62. A resilient member 70 is located at the bottom
of the hole or opening 68 abutting the wall of the cap 62. A
thermal conductive element 72 is fitted into the hole 68 and
pressed against the resilient member 70. It will be appreciated
that the element 72, when in place in the opening 58 in the cental
extension 66 of the cap 62, abuts the chip 64 forming an interface
74 therewith. The remaining open areas within the cap 62 are
evacuated and a helium gas 76 is placed therein under a small
positive pressure to prevent leakage of the ambient atmosphere into
the cap interior. This small positive pressure within the unit can
be maintained by including a helium capsule (not shown) within the
cap which has a predetermined small leakage rate. This gas 76,
being of a low molecular weight, seeps into the interface 74
between the thermal conductive element 72 and the chip 64, and also
seeps into the gap between the periphery of the element 72 and the
inside wall of the hole 68 in the central extension 66 of the cap
62. The thermal pressure actuator 70 if formed by an expandable
element, like a bellows, which includes therein a binary fluid
mixture of fluorocarbon liquids which engages changes phase at a
predetermined temperature, controlled by the mixing ratio. Thus, as
the heat generated by the chip 64 increases, the binary fluid
mixture temperature within the tubular member pressure actuator 70
will rise causing expansion of the associated thermal pressure
actuator and, thus, applying increased pressure on the thermal
conductive element 72. This increased pressure on the element 72
will make a tighter interface 74 between the chip 64 and the
element 72. As the pressure increases at this interface 74, the
thermal resistance goes down, thereby increasing the heat removal
from the chip 64. This thermal regulation tends to keep the chip
within it's operating range. The size and shape of the thermal
pressure actuactor 70 along with it's orientation with respect to
the thermal conductive element 72 can best be seen in FIG. 7 which
is a view taken along the line 7--7 of FIG. 6. If the module cap 62
surfaces do not prove sufficient for removing the heat generating
by the single chip, fins or a small coldplate can be easily
attached thereto. It should be noted, that the resilient thermal
pressure actuator 70 located behind the element 72 allows the
element to easily adapt to the height of the chip 64. It should
also be noted that the resilient thermal pressure actuator 70 in
conjunction with the peripheral gap 68 allows the thermal
conductive element 72 to adapt to the chip surface 74.
FIG. 8, in addition to showing the thermal path from the chip 46 to
the fluid 54 of the coldplate 50, shows a section of a helium
encapsulated conductive cooling unit having a mechanical or
pneumatic thermal actuator 76. The mechanical actuator 76, as
shown, can be a coil type spring which continually exerts pressure
against the thermal conductor element 44 forming a continual
pressure interface 50 between the element 44 and the chip 46. This
particular spring loaded thermal conductive element arrangement is
not self-regulating as was the unit containing the expandable
resilient member containing a gas which expands with temperature.
The space behind the thermal conductive element 44 could be filled
with a resilient material such as a foam, instead of a spring,
which would tend to apply a minimal pressure to the thermal
conductive element and just hold it more or less in position
against the chip. Such a low pressure interface would affect the
thermal resistance of the interface somewhat, but not enough to
make such an arrangement unusable in most cases. Of course, a
pneumatic thermal actuator rather than a mechanical arrangement
could also be utilized. The pneumatic thermal actuator could be
made self-regulating.
FIG. 9 is a graph wherein the thermal resistance from the chip 46
to the water 54 of the coldplate 50 in degrees centigrade per watt
is plotted against the thermal conductive element length in inches
for both aluminum and copper elements 44 and aluminum and copper
heat sinks as shown in FIG. 8. The heat sink includes the thermal
path through the cap and the abutting wall of the coldplate. All of
the plots on the graph were made using 0.180 inch square chips,
elements on 0.254 inch centers and holes in which the stud is
located having 0.260 inch centers. The interface between the chip
and the conductive element was maintained at 0.0005 inches. The top
plot or curve 78 was generated using an aluminum conductive element
and an aluminum sink. It can be observed that the thermal
resistance from the chip to the water in the coldplate tends to
drop off from a high of 18.degree. centigrade per watt for a o.2
inch long stud to a lowest resistance of approximately 15.6.degree.
centigrade per watt at an element length of 0.6 inches. For element
lengths longer than 0.6 inches the thermal resistance appears to
increase slightly. Accordingly, the optimum thermal conductive
element length for the particular chip, element and hole size
selected appears to be 0.6 inches. The middle curve 80 was obtained
using an aluminum thermal conductive element and a copper heat
sink. It will be appreciated that the thermal resistance is
generally lower indicating that the copper is a better heat
conductor than the aluminum. As would be expected, the third curve
82 provides an overall lower thermal resistance using a copper
element and a copper heat sink. It should also be noted in the
bottom curve that the lowest thermal resistance was obtained using
a thermal conductive element 0.9 inches in length.
The high heat conductivity of helium and the ability of helium to
fill gaps and interfaces, thereby providing a low thermal
resistance junction, have been utilized to provide a cooling unit
for solid state electronic chips which must be kept within a
specific thermal operating range. Also the inertness of the helium
gas makes it highly suitable for use in a cooling arrangement as
set forth above.
While the invention has been particularly shown and described with
reference to a preferred embodiment thereof, it will be understood
by those skilled in the art that the foregoing and other changes in
form and detail may be made therein without departing from the
spirit and scope of the invention.
* * * * *