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Second-Level Heat Sink with Package Warp Compensation

IP.com Disclosure Number: IPCOM000021038D
Publication Date: 2003-Dec-17
Document File: 3 page(s) / 55K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method that uses a second-level heat sink with a bottom surface that mirrors the surface/warpage of the package; this heat sink design creates a uniform TIM thickness or a thinner TIM Bond Line Thickness (BLT). Benefits include reduced thermal resistance through to the heat sink.

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Second-Level Heat Sink with Package Warp Compensation

Disclosed is a method that uses a second-level heat sink with a bottom surface that mirrors the surface/warpage of the package; this heat sink design creates a uniform TIM thickness or a thinner TIM Bond Line Thickness (BLT). Benefits include reduced thermal resistance through to the heat sink.

Background

Currently, Integral Heat Spreaders (IHS) have cavity and top-side surfaces with a target flatness of zero microns (i.e. a perfectly flat surface). The bottom surfaces of heat sinks also have targets that require them to be as flat as possible (see Figure 1). However, in an assembled package, the IHS or heat sink can warp significantly. The amount and nature of the warping depends on the coefficient of thermal expansion (CTE) of the package components, the thermal cycles seen in processing, pressure applied during processing, the overall package geometry, and the temperature profile of the package when power is applied to the die.

Differences in surface warping on the bottom surface of the second-level heat sink and the top surface of the IHS add up to create an uneven TIM thickness. In turn, this can result in locally increased thermal resistance and require a more expensive heat sink. Bowing of the heat sink or IHS, due to high clamping forces, can also cause uneven TIM BLT thickness.

Warping is currently solved by polishing/lapping the heat sink and IHS surfaces flat, so that they are more parallel to each other. Howev...