SELF-ALIGNING LIQUID-COOLING ASSEMBLY

Abstract: An assembly for cooling an array of IC packages (11) which have re­ spective non-planar heat dissipating surfaces (11a), comprised of: a frame that is attachable to the array and has multiple beams (14), each of which is positioned to overlie some of the IC packages (11); respective liquid-cooling jackets (15) for the IC packages with each jacket having a heat absorbing face (15a); each jacket being mounted via a post (18) that is loosely fitted through a respective hole in one of the beams in proximity with a respective one of the IC packages; and each jacket mounting providing a flexible con­ nection which allows the jacket's heat absorbing face (15a) to be placed at multiple angles and different heights, and thereby coincide with the non-co­ planar heat dissipating surface (11a) of an IC package (11).

Description: The invention relates to a liquid cooled assembly of integrated circuit components which are mounted on a substrate, said assembly including respective liquid cooling jackets for each of said integrated circuit components, manifolds and hoses that pass a liquid through said jackets, and a frame which holds said jackets against said integrated circuit components with springs. Many IC packages (e.g., ten to one hundred) are commonly mounted and interconnected on a printed circuit board. There the IC packages operate in conjunction with one another to perform various predetermined logic functions. For example, they may operate as a digital computer, or as a controller for a disk, or as a dynamic memory, etc. In any case, all IC packages dissipate heat; and so some means is needed to keep them from getting too hot. IC packages which dissipate just a small amount of heat need only be air-cooled; whereas IC packages which dissipate a large amount of heat must be cooled with some type of liquid-cooling assembly. However, due to various manufacturing tolerances, the orientation of each IC package on a printed circuit board can vary such that the surfaces of the IC packages which need to be cooled have different heights and different angles relative to each other. And for liquid-cooling assemblies, this presents a serious problem for since the differences in orientation can cause an IC package to misalign with its cooling assembly, and thereby produce a high thermal resistance. Also in assemblies for liquid-cooling IC packages, leaks can often occur due to various defects. Such leaks present another serious problem since they can cause electrical shorts and cause contamination. Further, assemblies for liquid-cooling IC packages tend to be complex and time-consuming to install; and that presents a problem since labor overhead must be minimized to stay competitive. For the same reason, a liquid-cooling assembly which is time-consuming to remove presents a problem since removal occurs whenever one of the IC packages becomes defective and has to be replaced. From US-A-4 558 395 a cooling module for integrated circuit chips mounted on a substrate is known. The assembly comprises a plurality of liquid cooling jackets for each of the integrated circuit chips, and the cooling jackets are interconnected by manifolds and hoses that pass a liquid through said jackets. In an embodiment of this module or assembly, a common holding cap is provided over all the cooling jackets, and a plurality of springs between the cap and the cooling jackets press these onto the integrated circuit chips. One end of each of the springs is bonded to the cap, whereas the other end is bonded to a holding plate for the cooling jackets. From US-A-3 481 393 another modular cooling system is known, in which series connected modular cooling chambers are provided each having a flat heat conducting side which is adapted for attachment to a respective flat backplate of an electronic module. Flexible hoses are connected between the outlets and inlets of the cooling chambers, so that these can be used for electronic modules of different heights and can also be easily detached from the backplate without interrupting the cooled fluid flow therethrough. In this known modular cooling system, the cooling chambers are mounted on the electronic modules by screws. It is an object of the present invention to provide a liquid cooled assembly which can be easily installed on integrated circuit components mounted on a substrate even if the components are misaligned. Furthermore, the assembly should be easily removable in order to permit replacement of integrated circuit components if necessary. According to the invention as set out in the appended claims, the liquid cooled assembly is characterized in that: a) said frame includes multiple beams, each of which is attached to said manifolds and overlies a portion of said integrated circuit components; b) each beam has holes which are proximately aligned with the integrated circuit components that the beam overlies; c) each jacket includes a guide post which passes through a respective one of said holes in said beams and a retainer that keeps the post in the hole; d) each post is loosely fitted in its hole such that the heat absorbing face of the corresponding cooling jacket can move up and down and tilt to coincide with said heat dissipating surface (11a) of an intergrated circuit component; e) said springs surround said posts and are compressed between said beams and said cooling jackets; and f) said manifolds, beams, jackets, hoses and springs are attached to and removable from said substrate, as one unit, solely by fasteners between said manifolds and said substrate. Various features and advantages of the invention are described herein in conjunction with the accompanying drawings wherein: FIG. 1 is a pictorial view of one preferred embodiment of the invention; and, FIG. 2 is an enlarged view of a portion of the embodiment of FIG. 1. Referring now to FIGURES 1 and 2, the physical makeup of a preferred embodiment of the invention will be described. In those figures, reference numeral 11 indicates three of the many IC packages that are on the printed circuit board 10; and the remaining reference numerals 12 thru 21 indicate the assembly for cooling the IC packages. In that assembly, the major components include an input manifold 12, an output manifold 13, multiple beams 14, respective liquid-cooling jackets 15 for each of the IC packages, and hoses 16 which carry liquid from the input manifold through the cooling jackets to the output manifold. Each of the beams 14 is attached at its ends to the manifolds 12 and 13. Also, each of the beams 14 has several holes 17 which are proximately aligned with a corresponding number of IC packages on the printed circuit board. Respective guideposts 18 are press fitted into each of the cooling jackets 15; and each guidepost passes through one of the holes 17. Each of the IC packages 11 has a heat dissipating face 11a; and the faces 11a of all the IC packages are at different heights and different angles relative to one another. These differences are caused, for example, by a) the IC package pins not being inserted fully into the plated-through holes of the circuit board, b) the IC package pins being inserted deeper into the board on one side of the IC package than on the other side, c) warpage of the circuit board, which may occur during the board fabrication process, or subsequently when the IC packages are soldered to the board, and d) variations in height of individual finished IC packages. Typical variations in the height of surface 11a is ±0.4mm (±0.016"). Factor a) above typically causes additional height variations of ±0.5mm (±0.02"). Also due to factor b) above, the angular orientation of surface 11a can typically be held only within ±5°. Combined with all of this is the bow and twist tolerances for the board itself, which for IPC Class A multi-layer circuit boards is ±5°. To compensate for all this variation in the orientation of each surface 11a, the guideposts 18 are loosely fitted in their holes. This allows each cooling jacket face 15a to tilt and simultaneously move up and down. Each post also has a retaining ring 19 which keeps the post in its hole. Respective springs 20 are compressed between each of the cooling jackets 15 and the beams 14 to force the heat absorbing face 15a of each cooling jacket against a heat dissipating surface of 11a of an IC package. Preferably, each beam 14 has a T-shaped or "+" shaped cross-section to resist deflection by the compressed springs. One embodiment of invention incorporates a 2.4mm (0,093") diameter guide post 18 centered in a 2.8mm (0.109") diameter hole 17 in the beam 14. This combination proximately places the cooling jacket 15 over the IC package; and it also permits ±12° of angular freedom for surface 15a, which is in excess of the maximum combined angular misalignment expected for surface 11a. Heat transfer between each IC package 11 and its cooling jacket 15 is critically dependent on intimate mechanical contact between face 15a of the cooling jacket and face 11a of the IC package. A thin film of thermal grease (e.g. 0.05mm/0.002" thick) can be used between the surfaces 11a and 15a to compensate for surface flatness deviation, but such a film cannot be made thicker to compensate for misalignments caused by factors a) thru d) above. Thermal analysis calculations show that increasing a thermal grease film thickness between the two surfaces 11a and 15a from 0.05mm (0.002") to only 0.1mm (0.004") will increase a typical thermal resistance of 0.50°C per Watt of IC package power to 0.63°C per Watt. Further increase in the grease film thickness caused by a worst-case angular mismatch of 10° (factors "b" and "c") on a 25.4mm (1") square IC package increases the thermal resistance to 5.7° per Watt, which is catastrophic! Another important feature of the above described cooling assembly is that it can be manufactured and pressure tested for leaks independent of the printed circuit board 10 of the IC packages 11. That is, components 12 thru 20 can be assembled and a fluid can be passed through them under pressure, prior to their attachment to the printed circuit board. This avoids leaks on the board and the accompanying disk of electrical shorts and contamination. Further, as FIG. 1 illustrates, attachment of the assembly to the board (as well as its removal therefrom) is a quick and simple procedure which only involves the insertion (removal) of a few screws 21 between the manifolds and the board.

Claims: A liquid cooling assembly for integrated circuit components (11) which are mounted on a substrate (10), said assembly including respective liquid cooling jackets (15) for each of said integrated circuit components (11), manifolds (12, 13) and hoses (16) that pass a liquid through said jackets (15), and a frame which holds said jackets (15) against said integrated circuit components (11) with springs (20); characterized in that: a) said frame includes multiple beams (14), each of which is attached to said manifolds (12, 13) and overlies a portion of said integrated circuit components (11); b) each beam has holes (17) which are proximately aligned with the integrated circuit components (11) that the beam overlies; c) each jacket (15) includes a guide post (18) which passes through a respective one of said holes (17) in said beams (14) and a retainer (19) that keeps the post in the hole; d) each post (18) is loosely fitted in its hole (17) such that a heat absorbing face (15a) of the corresponding cooling jacket (15) can move up and down and tilt to coincide with said heat dissipating surface (11a) of an integrated circuit component (11); e) said springs (20) surround said posts (18) and are compressed between said beams (14) and said cooling jackets (15); and f) said manifolds (12, 13), beams (14), jackets (15), hoses (16) and springs (20) are attached to and removable from said substrate (10), as one unit, solely by fasteners (21) between said manifolds (12, 13) and said substrate (10). An assembly according to claim 1 wherein each beam (14) has a non-rectangular cross section which is shaped to resist deflection by said springs. An assembly according to claim 2 wherein each beam (14) has a T-shaped cross section. An assembly according to claim 3 wherein the posts (18) with the retainers (19) and the corresponding holes have such dimensions that the orientations of the heat absorbing faces (15a) of the corresponding cooling jackets (15) can differ by more than five degrees. An assembly according to claim 1 wherein adjacent to each heat absorbing face (15a) a cavity is formed within the corresponding jacket (15) through which said liquid passes. An assembly according to claim 3 wherein said holes (17) in said beams (14), as well as the guide posts (18) of said cooling jackets (15) which pass through those holes, are disposed in two rows along each beam (14).

Inventors: ADRIAN GEORGE JOHN, NICOL EDWARD ALBERT, ADRIAN, GEORGE, JOHN, NICOL, EDWARD, ALBERT
Applicants: UNISYS CORP, UNISYS CORPORATION (A DELAWARE CORP.)
Application year: 1988
Main classification: H01L23
IPC codes: H05K7, H01L23