Exceptional performance from the development, qualification and implementation of a silicone adhesive for bonding heatsinks to semiconductor packages

The stress induced by the Coefficient of Thermal Expansion (CTE) mismatch of ceramic semiconductor packages bonded to aluminum heatsinks created a high risk of cracking. As packages increase in size and power, the need for an advanced adhesive with compliant properties, reliable bond strengths and high thermal performance is required. As a result of the work reported here, heatsink attach capabilities have been enhanced significantly with attractive cost benefits. Epoxy, silicone and polyimidesilaxoane adhesives were investigated for their process, material, reliability, and thermal performance. The project was divided into three phases: process development, qualification, and implementation. Concurrent engineering was emphasized to deliver a high-quality and low-cost process to production in a timely manner. In the initial development phase, over forty commercial and proprietary adhesives were evaluated based on the CTE, modulus and bond strength subjected to thermal cycling and moisture tests. A predictive thermo-mechanical and mechanical model was developed to define the required adhesive properties as a function of heatsinks weight and geometries. The wafer bow technique was used to estimate the induced stress from adhesive attach