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Method for a heatsink corner press pin

IP.com Disclosure Number: IPCOM000011517D
Publication Date: 2003-Feb-26
Document File: 6 page(s) / 323K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a heatsink corner press pin (HSCPP). Benefits include improved reliability, improved thermal performance, and improved mechanical performance.

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Method for a heatsink corner press pin

Disclosed is a method for a heatsink corner press pin (HSCPP). Benefits include improved reliability, improved thermal performance, and improved mechanical performance.

Background

        � � � � � Integrated heat spreaders (IHSs) are used on BGA packages to improve thermal performance and to reduce the BGA package coplanarity to within <8 mils. However, the installation of an IHS onto a BGA package increases package rigidity, which poses a higher risk to solder joint reliability from bending. Substrate warpage can occur at the package edge after ball attachment (see Figure 1). Severe solder cracking and failure can occur at package corners during shock and vibration testing. The rigid package is less flexible during board bending and leads to higher stress on solder joints at the package corners, which experience the highest deflection (see Figure 2). Three-point bend data from comparing packages with and without an IHS indicates that packages with an IHS have lower 3-point bending energy (see Figure 3). Packages with IHSs are more susceptible to solder joint cracking and failure.

        � � � � � Package loading is required because thermal interface material (TIM) must have a minimum pressure for thermal performance. However, high loading is a threat to solder joint reliability (see Figure 4) because it increases the tensile stress at the corner, making it sensitive to bending as with a rigid package. High load is required for thermal performance, but low load is required for mechanical performance. This conflict must be considered during product design.

        � � � � � One conventional solution is to constrain the board from bending by using a retention mechanism (RM, see Figure 5) and stiffeners on the board (see Figure 6). This solution increases the cost. (An RM is more expensive than a clip, which is a design that has failed.) Additional stiffeners installed on the board constrain board design and component placement. Stiffeners increase cost. The installation of RMs and stiffeners introduce another source of failure. Missing and broken screws can cause failure in vibration testing. These adaptations also constrain design flexibility.

General description

        � � � � � The disclosed method is a heatsink corner press pin (HSCPP). It is placed in the heatsink body and micro-spring-loaded to prevent deflection at the package corner/perimeter. The pin reduces/eliminates solder joint failure during shock and vibration testing and conditions, such as shipping and transportation.

        � � � � � The key elements of the method include:

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