Transient liquid phase sintered attach for power electronics

Low temperature transient liquid phase sintering (LT-TLPS) pastes, based on copper-tin, have been developed for high temperature attachment of wide band gap semiconductor dice to substrates for power electronics. The LT-TLPS attach process enables pressure-less joining at low temperatures in air. An organic binder has been used to form a stencil-printable paste that prevents oxidation of the copper and tin particles, before and during sintering. Shear samples have been manufactured consisting of copper dummy dice and copper substrates joined with a stencil printed layer of one of three copper-tin sinter pastes (viz. Cu60Sn, Cu50Sn, and Cu40Sn) having copper concentrations of 40%, 50%, and 60% by weight respectively. A high-temperature shear test setup has been designed to determine the shear strength of the three pastes at temperatures of 25°C, 125°C, 250°C, 400°C, and 600°C. It has been shown that the joints remain strong up to the melting point of the dominant intermetallic phase of the joint. Cu50Sn joints showed no reduction in shear strength up to 400°C, while Cu40Sn pastes showed no reduction in shear strength up to 600°C. This demonstrates that pressure-less LT-TLPS pastes can be used to form high-temperature resilient joints at low process temperatures in reasonably short process times.