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

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.