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Method for an Integrated Heat Spreader, heat pipe, and heatsink design to reduce the strain on the thermal and sealant material

IP.com Disclosure Number: IPCOM000006845D
Publication Date: 2002-Feb-06
Document File: 5 page(s) / 86K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for an integrated heat spreader (IHS), heat pipe, and heatsink design to reduce the strain on the thermal and sealant material. Benefits include improved thermal performance and improved reliability.

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Method for an Integrated Heat Spreader, heat pipe, and heatsink design to reduce the strain on the thermal and sealant material

Disclosed is a method for an integrated heat spreader (IHS), heat pipe, and heatsink design to reduce the strain on the thermal and sealant material. Benefits include improved thermal performance and improved reliability.

Background

              The conventional IHS sits on top of the flip-chip CPU substrate (see Figure 1). Because the IHS attaches to the edge of the substrate, stress is transferred from the substrate to the IHS, and the entire package warps (bows). Stress and strain occurs at the die/IHS thermal interface. As a result, reliability issues occur for the performance of solder, polymer, and polymer/solder hybrid thermal interface materials (TIM) in the OLGA flip-chip package. 

              The conventional IHS is designed to include a full-perimeter lip for attachment to the substrate (see Figure 2). This lip is greater in thickness than the cavity, 1.5 mm versus 2.13 mm at the lip. This form is very difficult to create in a single stamping process. For heat spreaders 38.5 mm in size, more than 8 progressive stamping die steps are required to form the lip and maintain a cavity thickness of 35 µm. The top surface flatness is often only achieved by an additional grinding step. The sealant is not mechanically linked to the IHS.

              The conventional IHS is typically manufactured from a high-purity copper alloy. This process is quite challenging with existing manufacturing (stamping) equipment limits, especially with respect to maintaining high raw material yield metrics and fully-filled corner geometries. To completely fill the corner locations of the IHS, typical industry raw material yields range as low as 35%, yet utilize multi-stage manufacturing with high-tonnage machinery.

Description

      The disclosed method is a low-cost flat heat spreader, heat pipe or heatsink design with pin attachment features for bonding or riveting the heat diffuser to the substrate or the heat spreader. The attachment pins are placed close to the die edge, along the edge of the thermal solution, or anywhere in between. The ability to locate the pin features close to the edge of the die versus the edge of the substrate decouples the entire substrate warpage to a fraction of the total warpage. Less strain is placed on the thermal material and thermal performance improves.  Strain on the sealant is reduced, and sealant delamination in highly stressed packages is eliminated.

              Pin attachment enables sealant application for large flat heat spreader or heatsink designs. The uniform thickness facilitates a one-stamping-tool operation at a low cost. The heat spreader or heatsink can meet flatness tolerances of 35 µm (cavity and top), which is difficult with a conventional IHS design greater than 31 mm in length and width.

      The key elements of the method ...