Enhanced test head liquid cooled cold plate

A cold plate, planar in shape, is machined to provide an interior cavity having a plurality of thermally conductive members which transfer any thermal energy absorbed by the cold plate to a chilled water stream flowing through the interior cavity. Electronic cards are mechanically and thermally married to copper conduction plates which mount on a surface of the cold plate. The cold plate can hold up to nineteen pairs of conduction plate/electronic card assemblies. Thermal energy generated by the electronic circuit cards flows into the conduction plate and then into the chilled water stream flowing in cold plate. The chilled water is provided by a cooling system as known in the art. The cold plate also provides a large central through-hole through which the electronic cards are electrically connected to a computer system. The cold plate through-hole allows the cold plate to enjoy close proximity to the thermal source providing a path of high conductance for the thermal energy to be dissipated.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is generally directed to providing reliable cooling 
systems for computer systems or for any electronic system requiring 
cooling. More particularly, the present invention is directed to the 
cooling of an enhanced test head which contains a very dense electronic 
package designed for test equipment manufacturers to test both logic and 
memory packaged products. 
2. Prior Art 
The test head electronics are required to perform these tasks in the 
shortest possible time and therefore particularly high heat fluxes are 
generated in the electronic package. Innovative solutions are necessary to 
handle these high heat fluxes and still maintain the integrated circuits 
within temperature specifications. 
A typical test head preferably occupies a 15".times.30".times.30" volume 
and generates approximately 8,000 watts of heat. This heat flux must be 
continually removed from this small volume to maintain integrated circuit 
temperatures at acceptable levels. To convey this heat from the test head 
an enhanced cold plate mated through conduction cooling to the electronic 
cards was developed. 
A refrigeration system employing a single cold plate which preserves flow 
isolation between the fluids in the redundant systems. In another aspect 
of the present invention, there is provided a combination of air and 
redundant refrigeration cooling for an electronic device such as a 
mainframe or server processing unit disposed within a cabinet possibly 
along with other less thermally critical components. In yet another aspect 
of the present invention, there is provided additional cold plates, each 
with its own array of electronic circuit cards to be cooled. The entire 
assembly is mounted on an articulated arm for movement to and from 
multiple test sites. The enhanced test head is capable of operating 
continuously in a variety of ambient conditions and under a variety of 
thermal loads. 
In recent years, the semiconductor industry has taken advantage of the fact 
that CMOS circuits dissipate less power than bipolar circuits. This has 
permitted more dense packaging and correspondingly faster CMOS circuits. 
However, almost no matter how fast one wishes to run a given electronic 
CMOS circuit chip, there is always the possibility of running it faster if 
the chip is cooled and thermal energy is removed from it during its 
operation. This is particularly true of computer processor circuit chips 
and even more particularly true of these chips when disposed within 
multi-chip modules which generate significant amounts of heat. Because 
there is a great demand to run these processor modules at higher speeds, 
the corresponding clock frequencies at which these devices must operate 
become higher. In this regard, it should be noted that it is known that 
power generation rises in proportion to the clock frequency. Accordingly, 
it is seen that the desire for faster computers generates not only demand 
for computer systems but also generates thermal demands in terms of energy 
which must be removed for faster, safer and more reliable circuit 
operation. In this regard, it is to be particularly noted that, in the 
long run, thermal energy is the single biggest impediment to semiconductor 
operation integrity. 
In addition to the demand for higher and higher processor speeds, there is 
also a concomitant demand for reliable computer systems and electronics. 
This means that users are increasingly unwilling to accept down time as a 
fact of life. This is particularly true in the demanding high pressure 
environment of electronic test equipment. Reliability in air-cooled 
systems is relatively easily provided by employing multiple air-moving 
devices (fans, blowers, etc.). Other arrangements which incorporate a 
degree of redundancy employ multiple air-moving devices whose speeds can 
be ramped up in terms of their air delivery capacity if it is detected 
that there is a failure or need within the system to do so. However, 
desired chip-operating power levels are nonetheless now approaching the 
point where air cooling is not the ideal solution for all parts of the 
system in all circumstances. While it is possible to operate fans and 
blowers at higher speeds, this is not always desirable for acoustic 
reasons. Accordingly, the use of direct cooling through the utilization of 
a refrigerant and a refrigeration system becomes more desirable, 
especially if faster chip speeds are the goal. 
While certain electronic components or modules produce relatively large 
amounts of thermal energy, it is often the case that these modules are 
employed in conjunction with other electronic circuit components which 
also require some degree of cooling but do not operate at temperatures so 
high as to require direct cooling via a cold plate and/or refrigerant 
system. If modules of varying thermal energy output are employed in the 
same system, it is therefore desirable that the cooling systems employed 
for the lower thermal output modules be cooled in a manner which is 
compatible with cooling systems employed for the higher temperature 
modules. To the extent that a degree of cooperation between these systems 
can be provided, the net result is a system which is even more reliable 
and dependable. Nonetheless, these dual cooling modalities may be 
accommodated within a single electronic card assembly. 
There are yet other requirements that must be met when designing cooling 
units for computer systems, especially those which operate continuously 
and which may in fact be present in a variety of different thermal 
environments. Since computer systems run continuously, so must their 
cooling systems unlike a normal household or similar refrigerator which is 
operated under a so-called bang-bang control philosophy in which the unit 
is alternating either totally on or totally off. Furthermore, since large 
computer systems experience, over the course of time, say hours, 
variations in user load and demand, the amount of heat which must be 
removed also varies over time. Therefore, a cooling unit or cooling module 
for a computer system must be able not only to operate continuously but 
also be able to adjust its cooling capability in response to varying 
thermal loads. 
SUMMARY OF THE INVENTION 
In accordance with a preferred embodiment of the present invention, an 
apparatus for cooling electronic circuits comprises a novel cold plate 
with a thermal interface to a plurality of conduction plates whereby each 
conduction plate transfers heat flux to the cold plate from its associated 
electronic circuit card. Each conduction plate is married to a single 
electronic card prior to being mounted on the cold plate. The conduction 
plate/electronic card pairs are then mounted perpendicular to and in 
parallel fashion onto the cold plate. The heat flux flows from the circuit 
card to the conduction plate and then into the cold plate. The cold plate 
has an internal cavity through which cold water is circulated to transfer 
the absorbed heat flux from the cold plate to a cooling system. The cold 
plate is shaped in a rectangular manner with a rectangular through-hole 
centrally located. As the conduction plate/electronic card pair is mounted 
onto the cold plate, one of the connectors mounted on the electronic card 
extends through the cold plate through-hole to mate with a matching 
connector. The cold plate through-hole is one of the essential novel 
elements that assists in rendering a compact design because it allows the 
cold plate to be in close proximity to all of the heat sources, i.e., the 
integrated circuits. 
The above-discussed and other features and advantages of the present 
invention will be appreciated and understood by those skilled in the art 
from the following detailed description and drawings.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 is a perspective view of a cold plate 2 made from copper 
illustrating the planar structure with a large central through-hole 3. 
Input port 8 and output port 9 are mounted on the top surface 20 at a 
front end 22 of the cold plate 2. Cold water is fed from a cooling system 
(not shown) to input port 8. The cold water flows in an interior cavity 4 
(see FIGS. 3, 4A & 4B) along path A to the rear end 23 of the cold plate 
2, crosses over to the opposite side in cross-channel 10 and returns to 
the output port 9 in a similar interior cavity 4. Thus, any thermal energy 
transferred to the cold plate 2 is absorbed by the cold water and 
transported to the cooling system. 
The cold plate 2 is mounted to an articulated test head platform (not 
shown) using the through-holes depicted in rows R.sub.1, R.sub.3, R.sub.4 
& R.sub.6 The holes depicted in rows R.sub.2 & R.sub.5 are not 
through-holes but are in fact bottomed within the cold plate 2. These 
holes, R.sub.2 & R.sub.5, are used to mount the conduction plate feet 44 
as shown later in FIG. 6. 
FIG. 2A is a top plan view of the cold plate 2 illustrating a central 
through-hole 3, various mounting holes 1 1, 12 & 13 and the input and 
output landings 15 & 16 for mounting the respective input and output ports 
8 & 9. The series of through-holes in rows R.sub.3 & R.sub.4 which 
surround the periphery of central through-hole 3, and the series of 
through-holes in rows R.sub.1 & R.sub.6 which lie near the periphery of 
the cold plate 2 are used to mount the cold plate 2 to the test head (not 
shown). The holes in rows R.sub.2 & R.sub.5 are for mounting conduction 
plate/electronic card pairs 70 as further described in reference to FIG. 
6. There are 38 holes in each row R.sub.2 & R.sub.5 labeled columns C, 
through C.sub.38. As can be seen in FIG. 2A, a conduction plate/electronic 
card pair 70 has been mounted in holes R.sub.2 C.sub.1, R.sub.2 C.sub.2, 
R.sub.5 C.sub.1, & R.sub.5 C.sub.2. In this manner nineteen (19) 
individual conduction plate/electronic pairs 70 can be mounted on each 
cold plate 2. A test head is usually comprised of four cold plates 2 so 
that a test head may have up to seventy-six conduction plate/electronic 
pairs 70 operating simultaneously. 
FIG. 2B is a side elevation view of the cold plate illustrating its planar 
structure with a view of an opening to the cross-channel cavity 10. During 
manufacture the cross-channel cavity is bored and reamed into the cold 
plate 2 from the cold plate exterior side wall 19. The cross-channel 
connects the two interior cavities 4A & 4B to form one continuous cavity 4 
throughout the cold plate 2. After the cross-channel cavity 10 has been 
machined, an appropriately sized end cap (see FIGS. 5A & 5B) seals the 
opening to the cross-channel cavity 10 on the cold plate exterior side 
wall 19. Mounting flange 18 extends beyond the exterior side wall 19 
(protrudes out of the page) so that mounting bolts passing through 
mounting holes 13 (see FIG. 2A) can secure the cold plate 2 to the test 
head (not shown). 
Referring to FIG. 3, a bottom plan view of the cold plate 2 is shown. The 
two interior cavities 4A & 4B with their depending array of fingers 6 are 
illustrated as the cover plates 14 (see FIG. 4B) are not yet in place. The 
interior cavities 4A & 4B are machined into the cold plate 2 along two 
parallel paths, each extending from a respective interior cavity front end 
24 & 25 to a respective interior cavity rear end 26 & 27 at a first depth. 
Next a CNC milling machine cuts deep grooves 50 and/or cross-cuts 52 into 
each cavity 4A & 4B (see FIGS. 4B & 4C) to define a plurality of fingers 
6. However front ends 24 & 25 and rear ends 26 and 27 of the interior 
cavities 4A & 4B are fingerless. In their respective cavity front ends 24 
& 25, through-holes 8A & 8B are bored to form the inlet port 8, and 
similarly through-holes 9A & 9B are bored to form the outlet port 9. The 
two cavities 4A & 4B are connected within the cold plate 2 by a 
cross-channel 10 bored into the plate 2 from a side edge as discussed 
above. The cold plate fluid path A begins at the inlet through-holes 8A & 
8B flowing into the inlet cavity front end 24, continues through the 
fingers 6 of inlet cavity 4A to rear end 26, traverses the cold plate 2 
through the cross-channel 10 to rear end 27, continues along outlet cavity 
4B to front end 25, and exits the cold plate 2 at the outlet through-holes 
9A & 9B. It 
Referring to FIG. 4A, a cross sectional view of FIG. 3 taken at AA" is 
shown. The fingers 6 are illustrated in the inlet interior cavity 4A and 
the outlet interior cavity 4B. It should be observed that the fingers 6 
are machined into the cold plate 2 so that their base 7 (see FIG. 4B) is 
connected to that portion of the interior cavity surface 5 which is 
directly under the cold plate top surface 20. Thus when the conduction 
plate feet 44 are mounted onto the cold plate top surface 20, there is a 
very short path of low thermal resistance between the conduction plate 
feet 44 and the cold plate fingers 6. This assures a very high thermal 
conductance between the conduction plate and the cold water flowing 
through the cold plate fingers 6 allowing very efficient heat flow from 
the integrated circuits to the cooling system. 
Referring to FIG. 4B, a first embodiment of a cross sectional perspective 
view of the cold plate 2 in FIG. 3 taken at BB" is shown with a cover 
plate 14 in near proximity. Only the first two rows of fingers 6 are shown 
but it should be noted that the rows of fingers 6 extend completely 
throughout the inlet cavity 4A and the outlet cavity 4B excepting their 
respective front ends 24 & 25 and rear ends 26 & 27. Chilled water flows 
along the interior cavities 4A & 4B in the grooves 50 and cross-cuts 52 
absorbing thermal energy from the surface area of each finger 6. 
Referring to FIG. 4C, a second embodiment of a cross sectional perspective 
view of the cold plate 2 in FIG. 3 taken at BB" is shown with a cover 
plate 14 in near proximity. In this embodiment only longitudinal grooves 
50 are cut by the milling machine along the interior cavity 4. Chilled 
water flows along the interior cavities 4A & 4B in the grooves 50 
absorbing thermal energy from the finger sidewalls. Each interior cavity 
4A & 4B is sealed by metallurgically bonding cover plates 14 onto 
shoulders 32 which will form an air-tight cavity from their respective 
front ends 24 & 25 to their respective rear ends 26 & 27. 
Referring to FIG. 5A, a side elevation view of a cross-channel end cap 17 
which attaches to the cold plate exterior side wall 19 to seal the 
cross-channel cavity 10 is shown. The end cap 17 sits in a shoulder 
circumferentially cut around the opening to the cross-channel cavity 10 on 
the cold plate side wall 19. The end cap 17 is metallurgically bonded to 
the shoulder to provide an air-tight seal. 
Referring to FIG. 5B, a top plan view of a cross-channel end cap 17 which 
attaches to the cold plate side wall 19 to seal the cross-channel cavity 
10 is shown. The oval shape and dimensions of the end cap 17 match the 
circumferential shoulder cut into the cold plate side wall 19. 
Referring to FIG. 5C, a side elevation view of a cover plate 14 is shown. A 
first cover plate 14 seals interior cavity 4A while a second cover plate 
14 seals interior cavity 4B (see FIG. 3). Each cover plate 14 sits in a 
respective shoulder 32 circumferentially cut around each opening of 
interior cavities 4A and 4B on the cold plate bottom surface 21. Each 
cover plate 14 is metallurgically bonded to its respective shoulder to 
provide an air-tight seal for its respective cavity 4A and 4B. 
Referring to FIG. 5D, a top plan view of a cover plate 14 is shown. The 
rounded comers and peripheral dimensions of the cover plate 14 match the 
circumferential shoulder 32 cut into the cold plate bottom surface 19 
around each interior cavity 4A and 4B. 
Referring to FIG. 6, a side elevation view of a cold plate assembly 80 is 
shown. An electronic card 60 is mated to its copper conduction plate 40 
and the conduction plate 40 is maintained in direct thermal contact with 
the integrated circuits (not shown) mounted on the electronic card 60. The 
conduction plate 40 has two feet 44, each of which is bolted to the cold 
plate 2 such that each foot 44 is mounted directly on top of an interior 
cavity 4 on the top surface 20 of the cold plate 2. Thermal energy 
generated by the integrated circuits flows to the conduction plate 40, 
disperses across the copper plate 40 to either of two heat pipes 46 and 
then downward to the conduction plate feet 44. The heat flux next flows 
from the feet 44 into the cold plate fingers 6 where it is transferred to 
the cold water stream and conducted out to the cooling system. Given that 
only one conduction plate/electronic card pair 70 is shown in this view, 
it should be noted that each cold plate 2 mounted on the test head can 
hold up to nineteen conduction plate/electronic card pairs 70 each. 
Each electronic card 60 has a first electrical connector 62 and a second 
electrical connector 63. The first electrical connector 62 of each card 60 
mates with a matching test head connector (not shown) which rises up 
through the cold plate central through-hole 3. The cold plate through-hole 
3 allows the cold plate 2 to enjoy close proximity to the integrated 
circuits mounted on the electronic card 60 providing a path of high 
conductance for the thermal energy to be dissipated thus lowering the 
volume requirement of the test head assembly while increasing the thermal 
efficiency of the cold plate simultaneously. 
Referring to FIG. 7A, a side elevation view of a port housing 53 which 
mounts on the cold plate 2 to form either an inlet port 8 or an outlet 
port 9 is shown. The front face 64 of the port housing 53 is preferably 
angled back 15.degree. to allow the axis 65 of the nipple aperture 54 to 
also be preferably elevated 15.degree.. This enhances an operator's 
ability to make and break the cooling conduit connections at the input 8 
and output 9 ports. 
Referring to FIG. 7B, a perspective view of FIG. 7A taken at line AA 
illustrating the port housing's front face 64 is shown. The nipple 
aperture 54 is preferably elevated 15.degree. from horizontal. The port 
end 58 of the quick disconnect nipple 57 will be pressed into the nipple 
aperture 54 to form an air-tight fitting. 
Referring to FIG. 7C, a bottom plan view of a port housing 53 is shown. A 
flow port 56 is formed on the bottom surface 55 of the port housing 53 and 
is in fluid communication with the nipple aperture 54 on the front face 
64. When the port housing 53 is mounted on the cold plate input port 
landing 15 or the output port landing 16, an air-tight fluid path is 
provided from the nipple aperture 54 to the interior cavities 4A or 4B of 
the cold plate 2. 
Referring to FIG. 7D, a side elevation view of a quick disconnect nipple 57 
is shown. The port end 58 is pressed into the nipple aperture 54 of the 
port housing 53 to provide an air-tight connection. The quick disconnect 
fitting 59 of the nipple 57 thereafter protrudes at a preferably upward 
angle of 15.degree. so that input and output coolant conduits may be 
attached to the cold plate 2. 
From the above, it should be appreciated that the systems and apparatus 
described herein provide a reliable redundant cooling system for computer 
and other electronic systems. It should also be appreciated that the 
cooling systems of the present invention permit the operation of computer 
systems at increased speeds. It should also be appreciated that the 
objects described above have been filled by the systems and methods shown 
herein particularly with respect to the utilization of a cold plate having 
dual flow-wise isolated but thermally coupled passages. 
While preferred embodiments have been shown and described, various 
modifications and substitutions may be made thereto without departing from 
the spirit and scope of the invention. Accordingly, it is to be understood 
that the present invention has been described by way of illustrations and 
not limitation.