Nanocomposite pastes for thermal and mechanical bonding

Heat dissipation is a major challenge in high performance electronic devices. Current thermal interface materials (TIMs) have either low conductivity, such as conventional thermal greases, or high costs, such as solder materials and indium metals. [1-2] We address TIM challenges by integrating silver nanoparticles (AgNPs) and copper micropowders (CuMPs) in a resin-free TIM paste. The nanocomposite TIMs optimize both the bulk and interfacial thermal performances: CuMPs with a particle size of 1-10 μm offer the promise of high bulk thermal conductivity, while AgNPs with a diameter of 3-8 nm provide the flexibility in interfacial engineering. The assembling temperature can be varied from 125 to 200 °C, due to the low sintering temperature of AgNPs. Fused AgNPs in the TIMs can form strong metallic bonds with CuMPs and the substrates, resulting in low interfacial thermal resistance and high mechanical bond strength. Morphological and compositional analyses have shown percolated network structures in the sintered TIM pastes, which are responsible for high thermomechanical reliability. Hybrid TIMs bonded between two metal substrates, such as a copper foil and an invar foil, with their linear coefficients of thermal expansion (CTEs) difference exceeding 15 ppm/ °C, have gone through more than 1000 cycles of thermal shocks between -50 and 150 °C without failure. The studies have shown promises of the hybrid TIMs for broader applications of thermal, electrical and mechanical performance in electronics packaging.