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Method for improving the thermal interface between the die and thermal solution by using a bimetallic strip heat-sink base

IP.com Disclosure Number: IPCOM000007586D
Publication Date: 2002-Apr-08
Document File: 3 page(s) / 145K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for improving the thermal interface between the die and thermal solution by using a bimetallic strip heat-sink base. Benefits include improved package reliability, reduced load variability, and improved thermal-interface effectiveness.

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Method for improving the thermal interface between the die and thermal solution by using a bimetallic strip heat-sink base

Disclosed is a method for improving the thermal interface between the die and thermal solution by using a bimetallic strip heat-sink base. Benefits include improved package reliability, reduced load variability, and improved thermal-interface effectiveness.

Background

Conventional solutions require packages to survive 100 lbf of static compressive load in its enabled configuration. This static force is place on the package during its entire lifetime. The purpose of this high force requirement is to reduce the thermal interface resistance between the package and the heat sink. A number of attractive package technologies (such as coreless and thin-core solutions) are no longer used due in part to their inability to survive 100 lb of static compressive load.

Description

The key elements if the disclosed solution include:

§         Pressure on the package increases progressively as the die gets hotter. A high pressure is required when the die is hot to efficiently cool down the die. A lower interface pressure when the die is cooler and when it is not operating does not impact the overall thermal design negatively.

§         The heat-sink base is comprised of plates of two materials attached together to form a bi-metal strip that curves in the center towards the package when the temperature of the system is increased. This construction used the principle of bimetal thermostats to force the base to change shape as the temperature changes.

§         The heat sink is attached to the package using conventional attachment schemes like springs connected to RMs. However, the spring need not provide the required static load. It only needs to restrain the heat sink during shock and vibration testing.

§         The thickness of the plates can be modified to provide the appropriate pressures for various designs.

              The disclosed method addresses the problem of the great pressure required to ensure a low thermal resistance between a package and a heat sink. This requirement causes several potential reliability issues to the package and the motherboard. Preventing the board from warping/breaking and applying forces in the order of 100 lbf while keeping the force variation small are challenging tasks.

              The conventional method is that stiff springs attach the heat sink to the package. The initial preload is used to apply the required force on the interface. The associated problems with this approach are:

§         Potential reliability issues due to the large compressive load, and over-design of the package to survive the high load

§         Increased preload variation due to variations in tolerance stack-ups

§         Elimination of viable package technologies like coreless and thin-core solutions due to the inability to survive the larg...