Nanoparticle Enhanced Solders for High Temperature Environments

Nanoparticle enhanced solders have been reported to have superior creep and reliability properties compared to simple alloyed materials. The nanoparticles, typically added at 1-2 wt% concentrations into the solder serve to harden the solder, stabilize the microstructure and improve reliability in high temperature environments. The nanoparticles may be added to the solder before production of solder particles, or added as a separate ingredient of the solder paste. This paper explores the latter approach. For this investigation, nanoparticles composed of a silica dielectric core and Au metallic shell were used, and the efficacy of different synthesis routes compared. In particular, it was found that poly diallyldimethyl ammonium chloride (PDADMAC), served as a better linker molecule than 3-aminopropyltrimethoxysilane (APTMS) for attaching the shell to the core. However, even with solder wettable shells, it was found that the majority of the particles were expelled from the SAC solder during reflow in air, and the causes were examined with the aid of computational fluid dynamics to model the reflow process.