Factors affecting wettability and bond strength of solder joint couples

The paper discusses the scientific understanding of the role of interfacial phenomena in joining of dissimilar materials using liquid-phase-assisted processes. From the example of the Sn-alloy/Cu system, it is demonstrated that interaction in the liquid solder/substrate couples is accompanied by a number of complex interfacial reactions leading to significant changes in the structure and chemistry of interfaces (solder/substrate, solder/environment, substrate/environment) and remaining solder layer that finally influence the mechanical properties of solder joints. The experimental data on wetting behavior, interface characterization, and mechanical properties of different solder/metal substrate couples are analyzed in order to display the role of such factors as time and temperature of interaction, environment (protective atmosphere, flux), presence of oxide films on interfaces, alloying additions to a solder, formation of interfacial phases, and porosity.