Multi-stud thermal conduction module

The thermal conduction module for removing heat from one or more chips located therein consists of a housing made of heat conductive materials forming a cap over the chips. The housing contains one or more openings, one opposite each of the chips. More than one heat conductive element is included in each of the openings and are free to move lengthwise within the opening. The heat conductive elements are spring loaded so that the end of each element contacts the associated chip thereby lowering the thermal resistance of the interface therebetween. Side spring means are located between the sides of adjacent heat conductive elements forcing them away from one another and into contact with the opening wall.

DESCRIPTION 
1. Technical Field 
This invention relates to a thermal conduction assembly or module for 
integrated circuit chips and, more particularly, to a thermal conduction 
module in which the heat transfer path from the chips to a heat sink is 
improved. 
In connection with integrated circuit chip thermal conduction modules, it 
is necessary to remove the heat generated by the circuitry on the chips to 
a heat sink, such as a cold plate which has cooling fluid continually 
circulating therethrough. Improving the heat conduction path from the chip 
to the heat sink not only allows a higher power chip to be utilized, but 
alternatively allows a simpler heat sink to be used. For example, a heat 
sink comprising heat dissipating fins located in a forced air stream can 
be used to replace the more complicated cold plate. 
2. Background Art 
With the miniaturized capabilities afforded by the discovery of solid state 
electronics, various improved means of dissipating the heat generated by 
solid state components has been investigated. The standard for forced 
convection means appears to have reached its limit of practicality in that 
the amount of air that is required to provide sufficient cooling to the 
limited heat dissipating surfaces introduces a noise problem, and without 
some auxiliary technique cannot maintain each of a large number of 
components within its critical, narrow operating temperature range. 
Accordingly, especially in connection with large scale computer systems, 
various innovative cooling systems have been devised. One of the more 
recent systems investigated has been the gas encapsulated cooling module 
of U.S. Pat. No. 3,993,123, issued Nov. 23, 1976, wherein an encapsulated 
cooling unit or module is provided which utilizes inert gas having good 
thermal conductivity as the encapsulated medium in combination with a 
conductive heat transfer arrangement. The integrated circuit chips to be 
cooled in the system are reverse mounted by connecting them face down to a 
substrate through solder balls. Because of this type of mounting, the chip 
is often slightly tilted. The tilt results in a poor surface contact 
between the conductive stud element and the back side of the chip. 
Accordingly, a high thermal resistance joint is formed which, in the case 
of the patent, required the insertion of a thermal conductive gas to lower 
the resistance. 
U.S. Pat. No. 4,156,458, issued May 29, 1979, sets forth a heat conductive 
metal foil bundle of sufficient thickness to contact sufficient surface 
area of the exposed back side of the chip to provide the required heat 
transfer, and which is sufficiently thin to be flexible enough to absorb 
differences in distance between the chip and the heat sink due to tilt as 
well as to expand and contract due to temperature changes, and which is of 
sufficient length to connect to the heat sink at or near the other end 
thereof. Good heat transfer was obtained using this arrangement, however, 
the large thickness of the bundle often adversely affected the flexibility 
and, therefore, exceeded the surface force limits established by the 
solder ball mountings. 
U.S. patent application Ser. No. 047,513, filed June 11, 1979, sets forth 
an improvement of the heat transfer between an integrated circuit chip and 
a heat sink by utilizing a matrix of pins mounted in a matrix of 
cylindrical openings in the housing adjacent the chips to be cooled. The 
pins have headers on the outer end thereof which contact the chip surface. 
Each pin is spring loaded individually to make individual contact with the 
chip surface with the required force. It should be appreciated, that each 
pin makes individual contact with the chip surface under individual spring 
loading so as to make contact regardless of the chip tilt. 
DISCLOSURE OF THE INVENTION 
In accordance with the present invention, improved heat transfer from one 
or more chips located in a heat conductive module is provided. The 
apparatus includes a housing made of a heat conductive material which 
forms a cap over the chip. One or more cylindrical openings are provided 
in the housing, one opposite each of the chips. More than one heat 
conductive element or stud is located in each of the openings, each of 
which is free to move independently. End spring means are located in the 
inner end of each opening for applying longitudinal force to each of the 
studs so that the end of the stud opposite the spring contacts the 
adjacent chip, thereby lowering the thermal resistance between the chip 
and the studs. Side spring means are located between the sides of adjacent 
studs forcing them away from one another and into contact with the opening 
walls to thereby lower the thermal resistance between the studs and the 
opening walls. It should be appreciated, that each stud makes individual 
contact with the chip surface and with the cylindrical opening wall under 
individual spring loading so as to make contact regardless of the chip 
tilt. 
The main advantage of the heat conduction module of the present invention 
is that the thermal conduction from the integrated circuit chips within 
the module is improved regardless of the chip tilt. 
Another advantage of the heat conduction module of the present invention is 
that the thermal resistance of the annulus gap between the studs and the 
housing cylindrical opening wall is lowered. 
A further advantage of the host conduction module of the present invention 
is that the temperature differentials within the circuit chips are 
diminished by providing additional heat transfer contact points thereon. 
Another advantage of the heat conduction module of the present invention is 
that the thermal conduction arrangement within the module is inexpensive 
and easy to manufacture.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring to FIG. 1, there is shown a partial cross-sectional view of a 
thermal conduction module 10 for providing heat removal from the 
integrated circuit chips 12 contained therein. As is well known, a chip 
consists of solid state circuits and devices which are densely packed 
thereon. 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 heat transfer must be of such character as to maintain the 
chip temperature within the required operating range. 
The chips 12 are mounted on one side of a substrate 14, generally made of 
ceramic, which has pins 16 extending from the other side thereof. These 
connecting pins 16 provide for the plugging of the module into a board 
(not shown) which may very well carry auxiliary circuits, etc. A housing 
or cap 18 is attached to the substrate 14 by means of a flange 20, which 
extends from the periphery of the substrate 14 to the cap 18. The cap 18 
is made of a good heat conductive material, such as copper or aluminum. 
The cap 18 contains a dead ended cylindrical opening 22 adjacent each of 
the chips 12. These openings 22 extend into the cap 18 from the surface 24 
facing the chips 12. FIG. 2 shows a 3.times.3 matrix of openings 22 
containing four heat conductive or stud elements 26 in each opening. These 
openings 22 have to be of sufficient depth and diameter to receive the 
required number of stud elements 26. Actually, the stud elements 26 can 
take various shapes, but the preferred shape is wedge shaped, since this 
shape maximizes the volume of the cylindrical opening 22 that is filled 
with the stud elements 26. The stud elements 26 are made of copper or 
aluminum or an alloy thereof because of their good heat conducting 
qualities. The number of stud elements 26 in each opening 22 is dependent 
upon a number of factors such as the amount of power consumed by the chip, 
the difficulty in manufacturing and assembly, etc. It should be 
appreciated, that the object is to contact as much of the chip 12 surface 
as possible with the stud elements 26. Accordingly, if there are a large 
number of stud elements 26 contacting the surface, the lateral dimension 
of the stud elements 26 will have to be relatively small to be included in 
the cylindrical opening 22 in the housing 18 adjacent the chip surface. 
Similarly, if fewer stud elements 26 are utilized in each cylindrical 
opening 22, the size can be increased accordingly. Each stud element is 
individually spring loaded by spring means 27 so as to exert a 
predetermined force against the chip 12 surface. The springs 27 are 
compressed against the end wall of the opening and the inner end of each 
stud 26, thereby providing lengthwise force on the studs urging them 
lengthwise out of the opening into contact with the adjacent chip. Further 
spring means 29 in the form of a leaf spring, are located between each of 
the studs 26 within an opening 22 forcing the studs 26 apart and into good 
thermal contact with the cylindrical wall of the opening 22. 
The thermal conduction module 10 shown in FIG. 1 contains a cold plate 28 
attached to the housing 18 which is the ultimate heat sink. The multiple 
studs 26 are believed to increase the heat transfer from the chips 12 
sufficiently, that a finned air cooling heat sink arrangement would be 
operable therewith. Because of the increased heat removal capabilities, 
the multiple studs 26 allow the use of a higher power chip 12. The 
multiple stud arrangement is also readily adaptable to the various known 
enhancements for improving heat transfer, such as the use of helium, 
grease, etc. in the gaps. 
A prior art arrangement of a single element stud 30 located in a 
cylindrical opening 32 in a housing 34 and spring loaded against a chip 36 
is shown in FIGS. 3 and 3a. The tilt of the chip in FIG. 3 is considerably 
exaggerated for purposes of illustration. Chips 36 mounted on solder ball 
connectors 38, as shown in FIG. 3, have a tendency to be slightly tilted 
as a result of this type of mounting. The prior art one piece stud 30 
extending from the cylindrical opening 32 in the housing 34 will contact 
the chips 36 at the highest point thereof. As can be seen in FIG. 3, this 
creates a large gap 40 between the stud 30 and the chip 36 which is 
ordinarily filled with air. Air is a well known good thermal insulator 
which provides a high thermal resistance in the gap 40 between the chip 36 
and the stud 30. A number of solutions have been proposed to solve this 
problem. For example, the module has been filled with helium gas which 
fills the gap 40 between the chips and the studs lowering the thermal 
resistance, since helium gas is a much better heat conductor than air. 
This solution introduced problems of containing the helium gas for the 
necessary length of time, since it is a highly permeable fluid. It has 
also been proposed that the end of the stud contacting the chip be 
outwardly curved or dished, thereby giving a predetermined area contact 
between the stud and the chip regardless of the chip tilt. It should be 
noted that the one piece stud 30 makes contact with the cylindrical walls 
42 of the opening 32 in which it is located at one or two places 44 with 
the rest of the circumference of the stud 30 forming an annular gap 46 
with the cylindrical wall 42 of the opening 30. This gap 46 can create a 
high thermal resistance, thereby, restricting the heat removal ability of 
the module. 
FIGS. 4 and 4a illustrate the features of the present invention which 
overcome the problems in the prior art, thereby, improving the heat 
transfer from the module. In FIG. 4a the tilt of the chip 50 is somewhat 
exaggerated to better illustrate the invention. A plurality of studs 52 
are shown located in a cylindrical dead-ended cylindrical opening 54 in 
the module housing 56. As can be seen in FIG. 4, there are six 
wedge-shaped studs 52 located in each cylindrical housing opening 54 
within the module. The outer periphery of the wedge-shaped stud 52, that 
is, the surface 58 opposite the pointed end of the wedge is curved with a 
similar curvature to that of the cylinder wall 60. The six wedge-shaped 
studs 52 are fitted together, as shown in FIG. 4, and inserted into the 
cylindrical opening 54 in the module housing 56. As shown in the 
cross-sectional diagram of FIG. 4a, each stud 52 makes at least a point 
contact with the chip 50 regardless of the tilt. There are now six areas 
or points of contact. It can be seen from FIG. 4a that the six points of 
contact not only improve the thermal conduction from the chip 50, but also 
reduce the size of the gap 62, thereby, further lowering the thermal 
resistance of the gap. This arrangement also has the advantage of 
distributing the points where the thermal conduction is concentrated about 
the surface of the chip 50. This considerably reduces the temperature 
differential (.DELTA.t) in the chip, thereby reducing stresses in the 
chip. 
Each of the studs 52 within an individual cylindrical opening 54 are spring 
loaded outwardly from the cylindrical opening 54 to provide a positive 
contact with the chip 50. The springs 64 not only hold the studs 52 in 
place against the adjacent chip surface, but provide a positive force of 
the stud 52 against the chip 50, which force has been found to enhance the 
heat transfer from the chip 50 to the stud 52. The spring 64 may be of the 
coil type, with one end thereof inserted in a cylindrical opening 66 
provided in the top of each stud 52. The other end of the spring 64 bears 
against the inner end of the cylindrical opening 54 in the housing 56, 
thereby, providing sufficient compression of the spring 64 when the stud 
52 is in place to provide the desired outward force on the stud. Since 
each stud 52 is free to move individually, the individual spring force 
provides the individual contacting force of each stud 52 against the chip 
50. 
An alternative spring 71 for the individual stud elements is shown in FIG. 
5. The arrangement is known as a crown spring 71 which consists of a band 
70 with the appropriate number of springlets 72 or curved portions made of 
spring material, such that the spring material portion bears against the 
top of one of the studs 52. Thus, the number of studs 52 determines the 
number of springlets 72. The crown spring 71 is inserted into the 
cylindrical opening 54 with the band 70 side first so that the springlets 
72 extend away from the bottom of the cylindrical opening 54 to provide 
the required spring force for each stud 52. The main advantage of this 
type spring lies mainly in the ease of assembly over against the handling 
of a number of individual springs 64. 
A blown up view of one of the studs 52 showing a side mounted leaf spring 
or springlet 74 is shown in FIG. 6. An indented groove 76 is located 
lengthwise along one side of the stud. The ends of the springlet 74 are 
attached to the bottom of the groove 76 at the appropriate distance from 
one another to provide the required bowing of the springlet. The springlet 
74 consists of a strip of spring material of sufficient resiliency to 
provide a small outward force from the side of the stud 52 from which the 
springlet extends. 
FIG. 7 is a blown up plan view in partial section looking in at one of the 
ends of the studs 52. Each of the springlets 74 extending from the side of 
the stud 52, when assembled will provide a force against the adjacent 
stud, which force causes the outer curved surface 58 of the stud 52 to 
make good contact with the cylindrical wall 60 of the opening 54 
containing the studs. As was mentioned above, contacting force at the 
contact area between two surfaces, enhances the thermal conductivity 
thereof. Accordingly, the springlet 74 on the side of each stud 52, when 
assembled, causes each of the studs 52 to make at least line contact with 
the cylindrical wall 60 of the opening 54. It should be appreciated that 
six areas of contact are provided, thereby, considerably reducing the 
annulus gap as indicated in FIG. 4. This considerably reduces the thermal 
resistance of the gap or interface between the studs 52 and the 
cylindrical wall 60 of the housing openings 54. The springlets 74 under 
severe pressure could fit within the groove 76 in the side wall of the 
stud 52. However, this kind of pressure is not contemplated. The 
essentially spring suspension of the studs 52 relative to one another 
within the cylindrical opening 54 reduces the friction between the stud 
side walls providing easier lengthwise motion of the individual studs 52 
so as to limit the end spring 64 force required to provide the force 
holding the studs 52 against the chip 50. 
As was previously mentioned, various enhancements can be applied to the 
module 10 such as outwardly curving or dishing the end of the studs which 
contact the chip, and filling the interfaces between the chip and the 
studs and the studs and the cylindrical walls of the housing with better 
heat conducting materials such as helium, dielectric liquid, wax, etc. 
While I have illustrated and described a preferred embodiment of my 
invention, it is to be understood that I do not limit myself to the 
precise construction herein disclosed and the right is reserved to all 
changes and modifications coming within the scope of the invention as 
defined in the appended claims.