Effect of bonding defects on heat transfer and creep response of microprocessor-heatsink adhesive joints

Abstract Efficient thermal management in microelectronic assemblies is crucial for the optimal performance and reliability of microprocessors. This study investigates the thermal, static, and creep performance of pressure-sensitive adhesives (PSAs) used in bonding heatsinks to microchips, focusing on the impact of adhesive coverage on thermal conductivity, mechanical strength, and long-term deformation under sustained loads. Shear loading, specifically analyzed due to the prevalence of shear stresses in vertically oriented microelectronic assemblies, is critical for understanding the long-term reliability of these bonds. The thermal analysis revealed that perfectly bonded heatsinks enhanced heat dissipation, with only a minor reduction in thermal conductivity observed due to incomplete adhesive coverage. Static tests demonstrated that perfectly bonded samples exhibited better load-bearing capacity overall, although joints with defects showed higher calculated stress due to the reduced bonded area at failure, with a 21% reduction in load-bearing capacity at room temperature and a 3.5% reduction at high temperature for joints with adhesive loss. Creep tests showed that at room temperature, the time to failure decreased by approximately 150% for samples with adhesive defects, while at high temperature, the reduction was over 66%. The study found that creep life is more sensitive to defects at lower temperatures, where adhesive loss has a more pronounced impact on performance. A predictive surface model was developed to estimate time to failure based on creep stress and temperature.