Process development of fast-cure low stress lid adhesive for microprocessors

A lid or heat spreader is used for packaging microprocessor chips. There are two primary functions for the lid: dissipate heat efficiently from the microprocessor and provide physical protection to the fragile silicon chip. To achieve these functions, lid material, thermal interface material and adhesive material, and assembly process are key areas that require development. Lid adhesive has a critical role in ensuring the whole microprocessor package meets thermal and thermomechanical reliability requirements. Lid adhesive has to provide good and consistent bonding strength between the lid and the substrate under various application conditions. At the same time, it also needs to absorb the stresses in the microprocessor package due to thermal mismatch between various materials: silicon, underfill, organic substrate, and lid. Another less known function of lid and adhesive is package warpage reduction. This paper discusses a low-stress lid adhesive material development that features a wide material processing window and fast-cure capability to improve assembly process throughput. Key material characteristics, including bonding strength, fracture mode, package warpage and reliability performance data will be presented to demonstrate the capability of the material to meet performance and reliability requirements for microprocessor packages.