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Low Thermal Resistance Tcm Using Stacked Cooling Inserts That Conform to Chip Tilt and Have Small Mechanical Gaps to the Cooling Hat

IP.com Disclosure Number: IPCOM000037375D
Original Publication Date: 1989-Dec-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 3 page(s) / 38K

Publishing Venue

IBM

Related People

Edwards, DL: AUTHOR [+2]

Abstract

A means for lowering the resistance of multichip module cooling inserts without losing the ability to conform to chip tilt is shown in the figure. By cutting a piston parallel to the chip face, a smaller mean gap between the hat hole and piston results for a given set of manufacturing tolerances. The resistance penalty of the additional interface is minimized by making the faces of both parts as flat as possible, or by introducing a material, such as Ostalloy (product of Arconium Corp.), and reflowing it. The net effect of the reduced mean gap and added interface is a reduced total thermal resistance.

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Low Thermal Resistance Tcm Using Stacked Cooling Inserts That Conform to Chip Tilt and Have Small Mechanical Gaps to the Cooling Hat

A means for lowering the resistance of multichip module cooling inserts without losing the ability to conform to chip tilt is shown in the figure. By cutting a piston parallel to the chip face, a smaller mean gap between the hat hole and piston results for a given set of manufacturing tolerances. The resistance penalty of the additional interface is minimized by making the faces of both parts as flat as possible, or by introducing a material, such as Ostalloy (product of Arconium Corp.), and reflowing it. The net effect of the reduced mean gap and added interface is a reduced total thermal resistance.

The following table details the nominal gap as a function of length for a conventional cylindrical flat-faced piston with and without anodization tolerances. Engagement Cylindrical Piston

Length Anodized Not Anodized

(mm) (mils) (mils)

4 .78 .70

6 .90 .82

8 1.01 .93

10 1.11 1.04

12 1.21 1.14

14 1.32 1.24

This table is based upon certain minimum clearances deemed necessary for large volume assembly. This table combined with the figure shows the reduced nominal gap achievable by stacking pistons. The dashed lines in the figure illustrate a conventional cylindrical piston which has a smaller diameter and wider gap to accommodate chip tilt. If, for example, the total engagement length is 12 mm, then a nominal gap (with anodization) is 1.21 mils. By splitting the pistons in half, one may expect two pistons each having a nominal gap of 0.9 mils. This is not entirely true. The piston closest to the chip will be at 0.9 mils, but the distant piston will be at 0.94 mils since we must introduce a perpendicularity tolerance onto the backside of the closest piston. Optimization of this example w...