Design optimization of custom engineered silver-nanoparticle thermal interface materials

Thermal interface material (TIM) is a major hurdle in heat flow for typical chip/heat sink assemblies. In many electronic devices, hot spots occur in areas of high activity during the device operation. These hot spots can lead to high thermal gradients, which in turn result in performance and reliability hindrances. The elevated, non-uniform power density confronted with conventional TIMs that contain a uniform layer of high thermal conductivity material for the entire chip can be extremely insufficient in many applications. In this paper, a custom engineered, Ag-nanoparticle (Ag-NP) TIM that targets directly to the high power density region is introduced for achieving better thermal-mechanical-electrical performance at low cost. These nanoparticles can be inkjet printed on hot spots and sintered at a relative low temperature (~120°C) to create a continuous metallic layer that is in good contact with both the chip and heat sink, whereas the conventional particle-laden TIM covers the lower power density area. A computational model is developed to examine the overall thermal performance and reliability of the hybrid Ag-NP/conventional TIM as a function of the bondline thickness, applied pressure, deposition pattern, and surface roughness. The results show great improvements compared with a high-performance indium solder.