CA1282187C - Liquid cooling system for integrated circuits - Google Patents

Liquid cooling system for integrated circuits

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Publication number
CA1282187C
CA1282187C CA000549537A CA549537A CA1282187C CA 1282187 C CA1282187 C CA 1282187C CA 000549537 A CA000549537 A CA 000549537A CA 549537 A CA549537 A CA 549537A CA 1282187 C CA1282187 C CA 1282187C
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Canada
Prior art keywords
liquid
cover
integrated circuit
spring
retaining means
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Expired - Fee Related
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CA000549537A
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French (fr)
Inventor
Kyle George Halkola
Jerry Ihor Tustaniwskj
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Unisys Corp
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Unisys Corp
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Priority to CA000549537A priority Critical patent/CA1282187C/en
Priority to CA000615761A priority patent/CA1303249C/en
Application granted granted Critical
Publication of CA1282187C publication Critical patent/CA1282187C/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Abstract

ABSTRACT OF THE DISCLOSURE
LIQUID COOLING SYSTEM FOR INTEGRATED CIRCUITS
A liquid cooled circuit module comprises an integrated circuit package 43; a cover 40 having a rim 40d which lies against the integrated circuit package 43, the cover 40 being shaped to form a passage for the liquid between the integrated circuit package 43 and the cover 40;
a retaining mechanism 42, which is fastened directly to the integrated circuit package 43, and which includes a member 42a that extends above the cover 40; and a spring 41, which is held in compression between the cover 40 and the retaining mechanism member 42; the spring 41 being adapted to press the rim 40d against the integrated circuit package 43 with at least a predetermined minimal force which prevents leaks and at the same time not exceed a stress limit in the spring.
In a second embodiment, a leak tolerant cooling system for cooling electrocial components with a liquid comprises: a frame 10 holding a plurality of printed circuit boards 11, each of which have electrical components attached thereto; a top reservoir 14, mounted on the frame 10 above the boards, for holding the liquid at atmospheric pressure; a conduit (17a-17g) coupled to the top reservoir and the boards, for conveying the liquid in a downward direction from the top reservoir over the components, the conduit being airtight in the absence of a leak therein; a bottom reservoir 15, coupled to the conduit below the boards, for receiving the liquid plus any air due to leaks from the conduit, the bottom reservoir being airtight except for a valve 16 which opens in response to a valve control signal S2; a pump 19, coupled to the bottom reservoir, for sucking the liquid and air through the conduit at sub-atmospheric pressures in response to a pump control signal S1, and for simultaneously returning the liquid to the top reservoir; and a control circuit 25 for generating the pump control signal starting when the liquid in the bottom reservoir is at a predetermined high level and continuing until the liquid in the bottom reservoir drops to a predetermined low level due to air leaking into the conduit, and for generating the valve control signal as the complement of the pump control signal.

Description

LIqUID COOLING SYSTEM FOR INTEGRATED CIRCUITS

BACKG ROUND OF THE I ~IE~T I ON
ThiY invention relates to systems for cooling electrical components; and more par~icularly, it relates to systems for cooling integrated circuit packages with a liquid in a digital compu~er.
Initially in the prior art, integrated circuits in digital computers were cooled by convection with air. Typi-cally, the integrated circuits of the computer w~re mounted on several printed circuit board~ which in turn were mounted in a frame. Then one or more fans were provided within the ~rame to simply blow air across the integrated circuits. Such a cooling ~ystem i5 relatively inexpensive;
however, it a~so ha~ several major limitations.
For example, as the amount of circuitry on.an inte-grated circuit chip increa~es, ~he amount o power and ~heamount of heat which tha~ chip dissipates also increa~es.
Thu~ a point is eventually reached with very large scale integrated circuits or with multichip in~egrated circuit packages at which the power dissipation is simply too high to allow cooling by air convection. ~lso, t~e logic gates in integrated circuit pàckages operate at slower speeds as their operating temperature is raised. Further, integrat~d circuits are more prone to failure when they are opera~ed at higher temperature.
Accordingly, in the prior art, systems for cooling integrated circuits by conduction with a liquid have been developed. One such system which IBM uses for example in their 3081 computers, consist~ essentially of a plurality of 3081 multichip cooling modules. Each module includes a base plate, a substrate with several integrated circuit chips, a piston holding plate, and a cold plate with water channels. These items are bolted together one on top of the other in the above recited order.
Formed in the piston holding plate are several cylinders, each of which contains a helical spring and a piston. In operation, each spring pushes a piston against a respective integrated circuit chip on the substrate; and heat from each chip then travels in a serial fashion through the piston, through the cylinder sidewalls, and into the cold plate to the water.
However, cooling in this IBM module is still sub-stantially limited because the water does not flow directly over the surface of the integrated circuit chips, and because thermal conduction between a piston and a cylinder sidewall i9 poor. In addition, liquid can leaX from the cold plate at its input port or its output port when a defective connection iq there made since the liquid passes through the cold plate under high pressure.
In another liquid cooling system, which is used in Cray-2 supercomputers, multichip circuit modules are completely immersed in a liquid bath. But this makes lt cumbersome to remove a module for repair. Also, only inert liquids can be used; otherwise conductive traces which `~ l,v2~

interconnect the circuit chips will corrode. Further, the liquid must have a very low dielectric constan-t so that electrical signals on the conductive traces do not propagate slowly. To meet these requirements, Cray-2 uses a special liquid called FC-77. But its surface tension is four times smaller than the surface tension of water; and this places considerable demands on the seals and gaskets in the cooling system - otherwise they will leak.

BRIEF SUMMARY
In accordance with a first embodiment, a liquid cooled circuit module comprises an integrated circuit package, a cover having a rim which lies against the integrated circuit package, the cover being shaped to form a passage for the liquid between the integrated circuit package and the cover; a retaining mechanism, which is ~astened directly to the integrated circuit package, and which includes a member that extends above the cover; and a spring, which is held in compression between the cover and the retaining mechanism member; the spring being adapted to press the rim against the integrated circuit package with at least a predetermined minimal force which prevents leaks and at the same time not exceed a stress limit in the spring.
In one embodiment of the module, the retaining mechanism includes headed pins which are fixedly attached to the integrated circuit package; the retaining mechanism member has tapered openings which are aligned with the pins and in which the headed pins removably lock; and the spring is adapted to maintain at least the predetermined minimal 82~

force on the rim and simultaneously not exceed the stress limit even under the condition where the spring is com-pressed by a variable distance due to several.manufacturing tolerances with~n the module.

In a second embodiment, a leak tolerant cooling system, for cooling electrical components with a liquid comprises: a frame holding a plurality of printed circuit boards, each of which have electrical com-ponents attached thereto, a top reservoir, mounted on theframe above the boards, for holding the liquid at atmos-pheric pressure; a conduit, coupled to the top reservoir and the boards, for conveying the liquid in a downward diraction from the top reservoir over the components, the conduit being airtight in the absence of a leak therein; a bottom reservoir, coupled to the conduit below the boards, for receiving ~he liquid plus any air due to leaks from the conduit, the bottom reservoir being airtight except for a valve which opens in response to a valve control signal, a pump, coupled to the bottom reservoir, for sucking the liquid and air through the conduit at subatmospheric pres-sures in response to a pump control signal, and for ~imultaneously returning the liquid to the top reservoir;
and a control circuit for generating the pump control signal startinq when the liquid in the bottom reservoir is at a predetermined high level and continuing until the liquid in the bottom re~ervoir drops to a predetermined low level due to air leaking into the conduit, and for generating the valve control signal a~ the complement of 3~ the pump control signal.

``` ~L2;~

BRIEF DESCRIPTION OF T_E DRAWINGS

Some embodimen-ts of the invention will now be described, by wa~ of example with reference to -the accompanying drawings in which:
FIG. 1 illustrates a leak tolerant liquid cooling system for electrical components;
FIGs. 2A-2D illustrate the operation of the FIG. 1 system under the condition where an air leak develops in a conduit within the system;
FIGs. 3A-3D illustrate the operation of the FIG. 1 system while a printed circuit board is removed from the system;
FIG. 4 is a set of equations which show how the FIG. 1 system operates at subatmospheric pressures when a pump in the system is running;
FIG. 5 is a set of equations which show how the FIG. 1 system operates at subatmospheric pressures when a pump in the system is off;
FIG. 6 is a sectional view of an embodiment of a cooling module within the FIG. 1 system;
FIG. 7 is a top view of the cooling module of FIG. 6;
FIG. 8 is a set of equations which describe how a spring within the cooling module of FIGs. 6 and 7 operates; and FIG. 9 is a sectional view of another embodiment of a cooling module which is suitable for use within the FIG. 1 cooling system.

DETAILED DESCRIPTION
A preferred embodiment of the invention will now be described in conjunction with FIG. 1. That embodiment includes a frame 10 in which a plurality of printed circuit boards 11 are mounted. Only one of the boards 11 is shown in FIG. 1, but the remaining boards are di~posed in a parallel fashion behind the illustrated board. These boards are held in place by card guides 12 and they plug into a backplane 13.
Also included in the FIG. 1 embodiment is a top reservoir 14 which is attached to frame 10 above the printed circuit boards. This reservoir 14 has an opening 14a which causes any liquid in the reservoir to be at atmospheric pressure. Lying below the printed circuit boards 11 is a bottom reservoir 15. This reservoir 15 is airtight except that it includes a valve 1~ which can be opened to place the bottom reservoir at atmospheric pressure.
A conduit 17 is also included in the FIG.
embodiment. It runs from the top reservoir 14, over the printed circuit boards 11, to the bottom reservoir 15. In operation, liquid from the top reservoir 14 passes through the conduit to the bottom reservoir; and in so passing the liquid cools the electrical components on the printed circuit boards.
Several parts 17a thru 17h make up the conduit 17 as indicated in FIG. 1. Items 17a and 17h are valved couplers; items 17b and 17g are flexible tubes; items 17c and 17f are metal or plastic manifolds; items 17d are cooling modules for the electrical components; and items 17e are tubes for interconnecting the cooling modules. A
separate conduit 17 is provided for each of the printed circuit boards.

3r~

Li~uid in the boktom reservoir 15 pas~es through a pipe 18 to a pump 19. Thi3 pump sucks the liquid ~rom the top reservoir through the conduit 17 to the ~ottom reser-voir. Then the pump 19 return~ the liquid back to th~ top reservoir 14 through a ~ipe 20, a hea~ exchangsr 21, and another pipe 22.
Two level 9en80r3 23 and 24, along with a relay circuit 25, are also included in the FIG. 1 sy~tem as shown. They control the operation o the pump 19 as well 10 as the valve 16. Sen~or 23 de~ects when the level of the liquid in the bo~tom re~ervoir 15 is at a predetermined high level, whereas sensor 24 detect3 when tha~ liquid i5 at a predetermined low level.
Circuit 25 responds to the level sensors 23 and 24 by generating a control ~ignal Sl on conductors 26a which turn the pump 19 on, beginning when the liquid in the bottom re~ervoir 15 is at the high level, and cont.inuing until the liquid in the bo~tom reservoir i8 at the low level. Durin~ this time, valve 1~ i8 closed.
Conver~ely, circuit 25 generates a control signal S2 on conductors 26b which open valve 16 beginning when the liquid in th~ bo~tom reservoir 15 i~ at the low level, and continuing until the liquid in the bottom reservoir reaches the high level. During thi3 time, pump 19 is off~
Reference should now be made to FIGs. 2A-2D which illustrate the operation of the FIG. 1 cooling sy~tem under the conditions where a ~mall leaX develop in the conduit 17 on one of the boards 11. Initially, as ~hown in FIG.
2A, there are no leaks, ~nd li~uid circulate~ through the 30 8y8tem in a normal ~a~hion. In thi~ state, the liquid is sucked by the pump 19 from the ~op reqervoir 14 through the respective conduits 17 on the printed circuit boards 11 to the bottom reservoir 15; and ~imultaneously, the liquid is pumped back to the top reser~oir.

~;~8~7 -a-Subsequerltly, as shown in FIG. 2B, a small leaX
develops in the conduit on one of the printed circuit board~ lli. rhi~ leak may be caused, for exasnple, by a ~aulty seal in a liqu~ d coo~ing module 17d or it could be 5 caused by a faulty connec~ion between a tube 17e and a cool ing modul e .
When such a leak occurs, fluid does not squirk out of the condui~. In~tead, air i8 sucked into ~che conduit 17 becau3e, a~ will be i e~p~ained in conjunction with FIG. 4, 10 the liquid flows through the eonduit 17 at 3ubatmo~pheric pressures. Air which i8 sucked into conduit 17 passe~ to the bot om re~ervoir 15 where it accumulate~. Thus, as shown in FIG. 2B, the liquid level in the bottom reservoir 15 drop~ at a rate which is proportional to the rate at which air i9 leaked into the conduit.
If the leaX i3 small in comparison to the size of the bottom reservoir 15, several hours may pa~s before the liquid in the bottom reservoir gets to the predetermined low level. During this time, the li~uid continues to flow through the conduit 17 and cool the electrlcal components on the printed circuit board~. Eventually, however, the ~tate of FIG. 2C i9 reached in which sensor 24 detects that the liquid level in the bottQm reservoir 15 is too low.
In response, pump 19 i9 turned off and valve 16 is opened. Consequently, liquid is no longer pumped from the bottam reservoir 15. But liquid does continue to flow from the top re~ervoir, due to gravity, through the conduit 17 and into the bottom reservoir 15. Thu9, as shown in FIG.
2D, tha bottom reservoir 15 begins to fill up, and this purges the air from the bottom resexvoir through valve 16~
When ~he liguid ~n the bottom re5ervoir 15 reaches the predeterm~ned high l~vel, it i3 detected by 8ensor ~3.
In response, pump 19 turns on and valve 16 close~. Thi~
returns the operation of the 8y5tem back to that which is 32~
_9_ shown in FIG. 2A. ThuY the system will co~tinue to cycle ~hrough the operating modes of FIGs. 2A-2D un~il the air leaX in conduit 17 i8 fixed.
Turning next to FIGs. 3A-3D, ~hey show a sequence by which board lli may be remo~ed from the sy~tem wi~hou~
interrupting the cooling 3y~tem's operation. Initially, as ~hown in FIG. 3A, board lli is disconnected ~rom th~ top reservoir 14. This is achieved via the valved coupler 17a as is shown in FTG. 1. Such a coupler should have a valve on the port which connect~ ~o the top re~ervoir 14 and no valve on the port which connects ~o the board lli.
When board lli is disconnected as shown in FIG.
3A, a large amount of air will be sucked through the conduit 17 on board lli into the lower reservoir 15. At the same time, any liquid in the conduit on board lli will drain in~o the lower re~ervoir.
Thus, a state is quickly reached, as shown in FIG.
3B, in which sensor 24 detects that the liquid level in the lower reservoir is too low. Then pump lg turns off and valve 16 open~. Conqequently, as ~hown in FIGo 3C, the liquid from the top reservoir 14 star~s to fill the bottom reservoir 15 due to gravity, and this purges the air from the botto~ reservoir.
During the time that the bottom reservoir is being filled, board lli with its empty condui~ 17 can be discon-nected from the bottom reservoir 15. This is achieved via the valved coupler 17h as shown in FIG. 1. Such a coupler should have a valve on the port whi~h connec~s to the bottom re~ervoir and no valve on the port which connects to the board.
FIG. 3~ ~hows the re~ult of the above disconnect-ing ~tep. Al~o, as ~hown in FIG. 3D, the ~ystem will continue to operate in its normal fashion with board lli removed after the Bengor 23 detect~ ~hat the bottom reservoir i3 full and turns pump 19 back on.

Consider now FIG. 4 which is a se~ of equation~
that shows how the pre~sure in the fluid of the FIG.
~ystem varies as it travels from the top r~servOir 14 to the bottom reservoir 15. Equation l is Bern~uilli'~ e~a-tion as applied to the FI5. 1 ~y~tem between two poin~s Ua"and "b". Point Ua~ i8 at the surface of the fluid in the top reservoir and point Ub~ i5 a~ an ar~itrary one of the components 17d and 17e on circui~ board ll. In equation 1, P is fluid pre~sure, ~ i3 1uid density, V i5 fluid velo-city, g i8 gravity, h is height, and L i~ presYure losses.
Equation 1 can be ~implified if the top reservoir14 i~ made large relative to the flow rate of fluid from that reservoir. Thi~ reduces the velocity of t~e fluid in the top re~ervoir to essentially zero as stated by equation 15 2. Substituting equation 2 into equation l and solving the result for the pressure Pb yields equation 3.
In equation 3, the term Pa i8 atmospheric pressure since the top reservoir 14 is open to the atmosphere.
Thus, in order for the pressure at point "b" to be subatmos-pheric, the 8Um of the two rightmost terms in equation 3must be larger than the third term from the right. This is stated by equation 4.
All of the remaining e~uations 5 thru 15 give an example of how the constraint of e~uation 4 can be met.
Initially, one Rhould pick the flow rate Q of the fluid through each of t~e cooling module~ 17d such that the electrical componentfl are properly cooled. For example, as stated in equation 5, one ~uitable Q i~ 25 milliliters per ~econd.
From the ~uantity Q, ~he total flow rate QT
through val~e 17a can be calculated simply by multiplying Q
by the number of parallel outpu~ portR from the manifold 17c. For example, if there are eight output port3, then the total 1OW rate QT through valve 17a is 200 milliliters per ~econd, as stated by equation 6. Thi8 flow rate QT i~
achleved by properly ~electing ~he pump 19.
Given QT, the preqsure drop acros~ valve 17a ean be calculated ba~ed on empirical data ~or ~he particular valve that i8 being employed. For example, when th~ ~low rate i9 200 milliliters per second, a series H single s~ut off valve having a one-half inch diameter from Snap-Tight, Inc. produces a pre3sure drop of 0.65 p3i . Thi~ is qtated by equation 7.
After the fluid passes through the valve 17a, it flows in a downward direc~ion to manifold 17c. Due to this drop in height, a pressure increase will occur. However, if the drop in height i8 suitably limited, then thi~ pres-8ure increase will not exceed the pressure drop in valve17a. For example, if the drop in height i~ 8ix inche~, then thi5 pressure increase will only be approximately 0.2 p3i a~ stated by equation 8.
Each time the fluid pa~qes through one of the cooling module~ 17d, additional pressure drops occur. Par~
of this pres ure drop i5 caused by the rapid expansion which the fluid undergoe~ when it enter3 the cooling module. This pressure drop can be expreqsed as an ex~an-sion head lo~a HE a~ tated by equation 9. In that equation, the term ke is a constan~ which dependq upon the ratio of the diameters of components 17d and 17e. For the diameter~ a3 stated by equation 10, ke i~ equal to 0.42.
Substituting that value of ke into equation 9 yields equa-tion 11 which s~ys the head 10~3 HE for the rapid expansion portion of component 17d i~ 4.05 inc~es.
Anoth~r pres~ure drop i8 al~o incurred each time the fluid leaves a cooling modul~ 17d due to the rapid con~raction which occur~. Thi8 pressure drop can b@

3'7 expres~ed as a` contraction head loss Hc as i9 stated by equation 12. In tha~ equation, kc i8 a constant which al50 depends upon the diameter of the component~ 17d and 17e.
For the diameter values ~iven by equation 13, kc equals 0.32. Substituting a kc f 0.32 into equation 12 yiPlds equa~ion 14 which ~ays the contraction head 109 HC is 3.07 inche~.
Thus the total head loss for one cooling module 17d i~ 4.05 inche~ plu3 3.07 inche~ or 7.14 inche~. This 0 i5 8tated by equation 15. So long a~ succe~ive cooling modules 17d are placed 1e33 than 7.14 inche~ apart, the pre6~Ure 105~e~ through ~ho~e module~ will be greatar than the pre~ure increa~e which is caused by the fluid's drop in ~eight as it passes from the top of the printed circuit lS board to the bottom.
Next, reference should ~e m~de to FIG. 5 which i8 a set of equations that de~cribe ~he operation of the FIG.
1 ~ystem under the condition where pu~p 19 is turned off and valve 16 i8 open. Thi8 condition occurs when fluid in the top reservoir 14 flow3 to the bottom reservoir 15 under the force of gravity to purge air from the bottom reservoir~
Un~er thi~ operating condition, it i~ again desir-able to have the fluid pres~ure in the cooling modules 17b to be subatmospheric ~o that the fluid does not squirt out o~ the conduit 17. Thus, ~he previously de~cribed con-straint of equation 4 in FIG. 4 must again be me~; and it i3 rewritten a~ equation 1 in F~G. 5. Equation 1 contain~
a 1088 term Lab which can be expre~ed as equation 2 wherein Xc i~ a constant for valv~ 17a; Vc i8 ~he velocity of the fluid a~ nter~ valve 17a; n i the number of cooling modules 17d to point "b"; Kb i~ a con~tant for one cooling module 17d; ~nd Vb i8 the fluid velocity as it enters through cooling module 17d.

~X~ 7 Based on the number of output ports from manifold 17c and the relative diameter~ of components 17b and 17c, the. fluid vel~cities V~ and Vc are related,a~ stated by equation 3. Substitutin~ equations 2 and 3 into equation 1 yields equation 4. There th~ velocity Vc is an unknown ~ince pump 19 i8 of f. However, the velocity V~ can be eliminated from equation 4 by applying Bernoulli'~ equation between points "a" and "e" in the FIG. 1 8y5tem, ~olving it for Vc, and substituting ~he result into equation 4.
Equation 5 i~ Bernoulli' 8 equation between pointq "a" ~nd "e". In it, pre~sure~ Pa and Pe are both atmos-pheric ~ince valve 16 i~ open; and velocity Va i6 again zero. T~i~ is ~t~ted by equation 6. Substituting equation 6 into equation 5 yields equation 7.
Included in equatlon 7 is a loss term Lae. It equals all of the lo.~se~ which the fluid undergoes a~ it travels from point "a" to point "e". Those lo~es can be expre~sed as equation 8 wherein N i8 the total number of cooling module~ 17d in one column on printed circui~ board 11; ~d is a con9tant for valve 17h;. and Vd is the fluid velocity as it enter~ valve 17h.
Based on the number of input ports to manifold 17f and on the relative diameters of components 17d, 17e and 17g, th2 velocities at point~ "c", "d" and "e" are related aY 8tated by equation 9. Substituting equations 8 and 9 into equation 7 yields equation 10. That equation can be ~olved or velocity Vc the result can then be substituted into equation 4; and this yieldR equation 11.
Equation 11 state~ a constraint on the ~ystem para-metera which, ~f met, will cause the fluid pressure in themodule~ 17d to be subatmo6pheric when pu~p 19 i~ not running. One way in which equation 11 can be met, as an ~xample, i~ a~ follows.

Let p-998 kg/m3 (water), KC-1798 ~g/m3, Xd=KC, K~396 kg/m3, Cb-1.929, Ce-l Cd-l ha'' he~~30~
ha-hb-6"+2n", ~=9, and n i~ an integer ~rom 1 to 9.
Substituting these values into equation 11 yield3 Table 1 below wherein XL i8 the value of the lefthand side of equation 11 in FIG. 5 and XR i8 the value of the righthand side of equation 11.

~able 1 n XL XR XL-XR XL/X~
1 2,686 2,230 456 1.204 2 3,269 ~,788 ~81 1.173 3 3, 851 3, 345 506 1.151 4 4,434 3,903 531 1.136 5,016 ~,460 556 1.125 6 5,599 5,018 581 1.116 7 6,181 5,575 606 1.109 8 6,764 6,133 631 1.103 9 7,346 ~,690 656 1.098 Turning now to FIGs. 6 and 7, the detailR of one preferred embodi~ent for cooling modula 17d will be described. Thi3 module includes a cover 40, a 6pring 41, and a retainer 42. Component~ 40, 41, and 42 are inter-coupled a~ 8hown and are attached to a ceramic integratedcircuit package 43 which encapsulates one or more inte-grated circuit chips. Details o packaga 43 are shown, for example, in U.S. patents 4,576,322 and 4,611,238.
Cover 40 include~ a concave-~haped member 40a, an input port 40b, and an output port 40c. Member 40a ha~ a rim 40d with a notch tha~ i~ fitted with an elastic seal ring 40e. That ~eal ring i~ compre~sed agains~ a flat 3urface 43~ of t~e integrated circuit package. Thu~ a passage is formed between surface 43a and the concave-shaped member 40a through which fluid can flow to cool the integrated circuit package.
Spring 41 is an arc-shaped leaf spring. Also spring 41 is wide at its center and narrow at its ends.
This is desirable because, as will be shown in detail in conjunction with FIG. 8, it allows the spring to maintain a certain minimal force on the cover 40 and simultaneously not overstress the spring even though various dimensions of the cooling module fluctuate from one module to another.
Retainer 42 includes a concave-shaped member 42a and a pair of headed pins 42b and 42c. Member 42a lies over the cover member 40a, and the pair of headed pins 42b and42c are rigidly attached such as by brazing to a metal pad on the flat surface 43a of the integrated circuit package. Also, retainer member 42a has a pair of flanges 42d and 42e with respective tapered openings 42f and 42g which are aligned with the headed pins 42b and 42c.
When the headed pins are in alignment with the wide portion of the tapered openings, retainer member 42a can be pushed downward on spring 41 such that the headed pins 42b and 42c pass through the openings 42e and 42f.
This distorts and compresses spring 41. Then, member 42 can be rotated clockwise by a few degrees such that the heads of the pins 42b and 42c overlie the narrow portion of the tapered openings 42c and 42d. In that position, the heads of the pins cannot pass through the openings. Thus the retainer member 42 is locked in place such that spring 41 compresses the seal ring 40d with a predetermined stress.
Consider now FIG. 8 which is a set of equations that describe the operation of spring 41. Equations 1 is obtained by summing the forces which act on the cover 40.
In equation 1, FSP is the force which the spring exerts on the cover 40; P is the gauge pressure of the fluid as it . -16-flow~ through ~he cover 40 (the difference between th~
absolute fluid pressure and atmospheric pressur~), A is the surace ar~a of the cover 40 on which -~he pressure P acts $n a vertical directio~; and FSR i8 the force with which the seal ring 4~e i8 cQmpres~ed a~ai~t surface 43a.
Pre~sure P is determined by the analy~is which was previously described in conjunction with FIG. 4. Area A is determined by the size of the concave-~haped member 40a.
And a minimum ~alue for force FSR i8 ~elec~ed such that the 5eal ring 40e will not leak.
Force Fsp can also be expressed in terms of a spriny constant X times the deflection D of the end6 of the spring 4l. Thi8 i~ ~tated ~y ~quation 2. Sub tituting equation 2 into equation 1 yields equation 3.
In equation 3, the deflection D varies between a minimum valu~ Dmin and a maximum valu~ DmaX~ Those values depend upon various manufacturing tolerance~ for the compo~
nent~ 40a, 42a, 4~b and 42c. For example, the deflection D
i3 smaller than nominal if components 42a, 42b and 42c are taller ~han nominal and component 40a i9 -~horter . than nominal.
When the mi~imal deflec~ion Dmin occur~, the forc~
w~ich ~pring 41 exer~s mu~t till be greater than the fluid force PA plu~ ~he minimum force FSRmin that need~ to be maintained on the ~eal ring 40e in order to prevent leaks.
This, as ~tated by equation 4, i~ one constraint which must be met by ~pring 41.
In equation 4, the ~pring con~tant term k can be expres~ed in terms of the phy~ical parameters of the ~pring 41. This i3 doné via equation 5. Ther~, L i~ ~h~ length of the Bpring; W9 iS ~he width o the ends of ~he spring;
Wb is the width of ~he cen~er of the spring; h i~ ~he thick ne~ of the sprlng, and E 1~ the modulus of elasticity of the material from which the ~pring iB made.

~7 Another constraint which mu~t be met by ~pring 41 concern~. the maximum ~tres~ S that occura in the spring.
Thi~ ~tress S occurs at the center o~ the ~pring. ~quation 6 giv~s an expres~ion ~or ~he skress S in terms o~ the force F5p which the spring e~ert~ and its physlcal para-meters L, w8, and h. ~gain, ~he force ~SP which the ~pring exerts i8 equal to the ~pring constant k time~ the distance D by which the ends of the spring are defl~cted. This was stated above in equation 2. Substituting equation 2 into e~uation 6 yields equation 7.
In equation 7, the deflection D will have a maxi-mum value DmaX when components 42a, 42b and 42c are manufactured rela~ively short and componant 40a i~ rela-tively tall. When that occurs, the stress S must still be le~g than a value SmaX at which ~he 6priny will permanently deform. This, a~ stated by equation 8, i~ a second con-~traint which must be met by spring 41.
As ha~ been e~plained above, the pres~ure P of ~he fluid under normal operating conditions will be subatmo~-pheric. Thus, under normal op~rating condition3, the termPA in equation l i3 negative; and this makes the con-straints of equations 4 and 8 easier to meet than if the term PA was positive. So, for the purpose of dPmonstrating how the spring 41 operate3 under "worst ca~e" conditions, as6ume now that the pressure P i~ above atmosphericO
For example, suppose PA i0 13.5 pound~; FS~min i5 1.5 pounds: Sm~s is 180 XPSI; ~max is D nominal plu~ 0.015 inches; Dmin i~ D nominal minuB O.015 incheq; and D nominal i~ 0.190 inches. Under ~uch condition~, the con~train~s of e~uation~ ~4 and -48 can be met ~y making wb-1.5 inche6, w~-O.25 inche~; h-0.015 inches; LF1.5O inche~; and Es20.33~10e~p6 which i8 E for BeCu. These values caUce ~he minimum spring force to be 16 pounds (which iB greater than 13.5~1.5), and they cau~e ~he ma~imum ~pring stre3~ o be 3~ 120 KPSI (which ~8 les~ than 180 XPSI).

32~

Ne~t, referring to FIG. 9, ~till another preferred em~odiment of the cooling module 17d will be de~cribed in detail. Thi3 module includeR a cover 50, a spring 51, and a retainer 52 which are intercoupled to each other and atta~h to an integrated circuit package 53 a4 ahown.
Cover 50 ia similar in ~hape to the previously described cov~r 40. Xt inGlude~ a conc~Ys-~haped member 50a, an input par~ 50b, a~d an output port (not shown, but which is in alignment with the input port 50b and in froat of the spring 51). Cover 50 al50 has a rim 50d with a notch that is fitted with an elaRtic seal ring 50e. A
pas~age through which the fluid flow.~ i~ formed by the concave member 50a, the seal ring 50e, and the surface 53a of the integrated circuit pac~age.
By comparison, the r~tainer 52 has a totally dif-ferent shape than the previously described retainer 42.
Instead of being concave-~haped, it i~ uniform in width in a direction perpendicular to the plane o FIG. 9. Thus retainer 52 con~ists of one uniform width member 52a which lies above cover 50 and two ho~k-shaped legs 52b and ~2c which ex~end from member 52a and clamp onto the bottom of the in~egrated circuit package 53. When the legs 52b and 52c are clamped to package 53, member 52a deflects ~pring 51 which in turn exert~ a force of predetermined magnitude on cover 50 such that the seal ring 50e does not leak.
Var~ou~ preferred embodiment~ of the invention have now been degcribed in de~ail. In addition, however, many changes c~n be made to these detail~ without departing from the ~atur~ and ~pirit o the invention. For e~ample, in the opening 14a of re~ervoir 14 in FIG. 1, a compliant membr~ne could be added to preve~t contaminants from reach-ing the ~luid and to prevent ~he fluid from evaporating.
Accordingly, the inv~ntion i~ not to be limited to the described detailed embodiments but ~ 9 defined by the appended cla~m~.

Claims (10)

1. A liquid cooled circuit module, comprising:
an integrated circuit package;
a cover having a rim which lies against said integrated circuit package, said cover being shaped to form a passage for said liquid between said integrated circuit package and said cover:
a retaining means, which is fastened to said integrated circuit package, and which includes a member that extends above said cover; and a spring, which is held in compression between said cover and said retaining means member; said spring being adapted to press said rim against said integrated circuit package with at least a predetermined minimal force that prevents leaks and at the same time not exceed a stress limit in said spring.
2. A module according to claim 1 wherein said retaining means includes headed pins which are fixedly attached to said integrated circuit package, and wherein said retaining means member has tapered openings which align with said pins and in which said headed pins removably lock.
3. A module according to claim 1 wherein said retaining means member has hook-shaped legs which clamp onto said integrated circuit package.
4. A module according to claim 1 wherein said spring is adapted to maintain at least said minimal force on said rim and simultaneously not exceed said stress limit, under the condition where the amount by which said spring is compressed varies due to manufacturing tolerances within said cover and said retaining means.
5. A module according to claim 1 wherein said spring is a leaf spring having a wide center and narrow ends.
6. A module according to claim 1 wherein said rim is fitted with an elastic seal ring.
7. A module for cooling an electrical component with a liquid, comprising:
a cover having a rim which is shaped to lie against said electrical component and in such position form a passage for said liquid between said electrical component and said cover;
a retaining means, which fastens to said electrical component, and which includes a member that extends above said cover; and a compliant means, which is held in a distorted fashion between said cover and said retaining means member to press said rim against said electrical component with at least a predetermined minimal force that prevents leaks.
8. A module according to claim 7 wherein said retaining means includes headed pins which fixedly attach to said electrical component, and wherein said retaining means member has tapered openings which align with said pins and in which said headed pins removably lock.
9. A module according to claim 7 wherein said retaining means member has a hook-shaped legs which clamp onto said electrical component.
10. A module for cooling an electrical component with a liquid, comprising:
a cover having a rim which is shaped to lie against said electrical component and in such position form a passage for said liquid between said electrical component and said cover;
a retaining means, which fastens directly to said electrical component; and a compliant means, which is connected between said cover and said retaining means and is adapted to change in shape to hold said rim against said electrical component with at least a predetermined minimal force that prevents leaks.
CA000549537A 1986-10-14 1987-10-16 Liquid cooling system for integrated circuits Expired - Fee Related CA1282187C (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
CA000549537A CA1282187C (en) 1987-10-16 1987-10-16 Liquid cooling system for integrated circuits
CA000615761A CA1303249C (en) 1986-10-14 1990-06-01 Liquid cooling system for integrated circuits

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CA000549537A CA1282187C (en) 1987-10-16 1987-10-16 Liquid cooling system for integrated circuits

Related Child Applications (1)

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CA000615761A Division CA1303249C (en) 1986-10-14 1990-06-01 Liquid cooling system for integrated circuits

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CA1282187C true CA1282187C (en) 1991-03-26

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116294301A (en) * 2022-12-05 2023-06-23 大连理工大学 Pump-assisted capillary force driven two-phase fluid heat management system

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116294301A (en) * 2022-12-05 2023-06-23 大连理工大学 Pump-assisted capillary force driven two-phase fluid heat management system
CN116294301B (en) * 2022-12-05 2024-05-03 大连理工大学 Pump-assisted capillary force driven two-phase fluid heat management system

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