Preform-based diffusion soldering for use under conventional soldering process parameters

The diffusion soldering process has attracted much interest following the development of new wide band gap materials, such as SiC chips as well as the need to address the higher reliability requirements of emerging power electronics applications. This paper introduces novel composite materials as preforms based on diffusion soldering. The composite materials concerned consist of alternating multi-layer systems of lead-free solder and high melting point metals like Copper (Cu). The thickness of the lead-free solder layers is always less than 5 μm, whereby the total thickness of the composite material ranges from 50 μm to 300 μm. This novel composite material enables full formation of inter-metallic phases (IMPs) in the lead-free solders layers during the conventional soldering process with a short-term max. peak temperature of 250°C; (< 5 min) without using any pressure and no post-heating requirements. The re-melting temperature of the resulting structure of the composite material is higher than 400°C.