Performance of Sn-3.0Ag-0.5Cu composite solder with TiC reinforcement : Physical properties, solderability and microstructural evolution under isothermal ageing

This paper is focused on the effect of TiC nano-reinforcement that was successfully introduced into a SAC305 lead-free solder alloy with different weight fractions (0, 0.05, 0.1 and 0.2 wt%) through a powder-metallurgy route. Actual retained ratios of TiC reinforcement in composite solder billets and solder joints were quantitatively analysed. The obtained SAC/TiC solders were also studied extensively with regard to their coefficient of thermal expansion (CTE), wettability and thermal properties. In addition, evolution of interfacial intermetallic compounds (IMCs) and corresponding changes in mechanical properties under thermal ageing were investigated. Only about 10%-30% of initial TiC nanoparticles added were found retained in the final composite solder joints. With an appropriate addition amount of TiC nanoparticles, the composite solders exhibited an improvement in their wettability. A negligible change in their melting point and a widened melting range were found in composite solders containing TiC reinforcement. Also, the CTE of composite solder alloys was effectively decreased when compared with the plain SAC solder alloy. In addition, a growth of interfacial IMCs in composite solder joints was notably suppressed under isothermal ageing condition, while their corresponding mechanical properties of composite solder joints significantly outperformed those of non-reinforced solder joints throughout the ageing period.