Modeling heat transport in thermal interface materials enhanced with MEMS based microinterconnects

Thermal management of device level packaging continues to present many technical challenges. In the typical chip heat sink assembly, the highest resistance to heat flow comes from the thermal interface material (TIM). The thermal conductivities of TIMs remain in the range of 1-4 W/mK due to the properties and structure of small dispersed solids in polymer matrices. As a result of the rising design power and heat flux at the silicon die, new ways to improve the effective in situ thermal conductivity of interface materials are required. This paper will introduce a unique TIM enhanced with ultrahigh density wafer level thin film compliant interconnects named smart three axis compliant (STAC) interconnects. The MEMS technology based STAC interconnect is directly fabricated onto a silicon wafer and embedded into the TIM to provide an enhanced conductive path between the die/package and the heat sink. Numerical and analytical analyses of the thermal conduction in the TIM embedded with STAC interconnects are performed. The objective of the study is to provide comprehensive design strategies for effective implementation of this type of TIM for specific applications. Parametric studies are conducted to examine the thermal conductivity of the microinterconnect enhanced TIM for varying materials, configurations, and geometry of the microinterconnects. For the modeling, a periodic element model of chip-TIM configuration with top heat sink is developed and maximum temperatures are determined in order to evaluate the conductive effect of the microinterconnect. In addition, an investigation of the conductive transport in a more complicated chip stack is considered. A 3-D thermal analysis is conducted for a multi-chip stack package with and without through-silicon-vias. The numerical results show that the microinterconnects significantly improve the thermal performance of the TIM. Finally, further steps toward achieving a chip-level design optimization and fabrication process using microinterconnects structured TIM is proposed.