Impact of Lifetime and Mechanical Behaviors on TIM Performance for High-End Processor

Power density growth of the IC packages highlighted the importance of the thermal management. While there are dimensional limitations in designing the thermal solution, it is known that conductivity of the TIM plays a primary role to improve the thermal performance. However, multi-layered structure of TIM1-Lid-TIM2, assembly process challenge, and mechanical behavior of components in the lidded packages significantly limit the impact of the TIM thermal conductivity. This study investigates limitation of the lidded package and suggest the practical method to improve the thermal performance of the large size stacked die package. Due to the die warpage and surface roughness of the heat spreader, TIM is required to ensure the surface contact between the two surfaces. However, process challenge and thermal shrinkage during the lifetime decrease TIM coverage area and degrade the performance. Hence, understanding thermomechanical behavior of the TIM together with package behavior and relation to the performance during lifetime are the key factor to the successful thermal management for high-end IC device. In this study, thermal performance change depends on the mechanical behavior of TIM from time 0 to TCB1200 are investigated to find the impact of lifetime and mechanical behaviors on TIM performance. Four commercial TIM 1 with thermal conductivity range from 2W/mk to 5W/mk are selected to build test vehicles. The die size of the thermal test vehicle is 20mm × 20mm and thermal contour of the die can be generated by embedded sensors in every 0.25mm2. Heatsink is mounted on the top of the package and identical TIM 2 are applied on all the samples. At time 0, die temperature change over the time are monitored with varying airflow cooling. After 1200 TCB, temperature changes are also observed with the same set up to obtain the thermal performance data of different TIMs depends on thermal cycling effect. At both stage for time 0 and TCB1200, TIM coverage, BLT, and package warpage are measured to find the correlation among the mechanical behavior and lifetime to the thermal performance. From the empirical data, the TIM coverage on the die area has the most impact on the thermal performance over the thermal conductivity among the selected materials. Adhesion strength is the dominant factor on high coverage and highest adhesion strength material shows the least degrading thermal performance from time 0 to TCB1200.