Impact of additives and silver methanesulfonate concentration on the preparation of Sn–Ag–Cu micro-bumps

Abstract

In this study, Sn–Ag–Cu solder micro-bumps were successfully prepared on copper mask substrates with a diameter of 100 µm by electrodeposition process. We systematically compared the effects of different leveling agents and surfactants on the microscopic morphology and chemical composition of electrodeposited coatings. We analyzed the role of additives on the polarization behavior of the plating solution using polarization curves. The impact of silver methanesulfonate concentration on the plating coating was also investigated. The experimental results indicate that when employed individually as a leveling agent in the plating solution, methanol or triethanolamine exerts a significant effect on enhancing the smoothness of the plated coating and increasing the polarization of the plating solution. However, it is worth noting that when the two leveling agents co-exist, it leads to a decrease in the cathodic polarization and an increase in the silver content. It was further found that combining methanol and surfactant OP-10 in appropriate ratios could increase the cathodic polarization and promote grain refinement. Electrodeposition at low concentrations of silver methanesulfonate resulted in dense and uniform Sn–Ag–Cu coatings with good overall consistency, and the silver content of the coatings was as low as 1.63 wt%. The prepared plating coating features uniform element distribution, and the intermetallic compounds show good uniformity in distribution and size after reflow soldering, indicating excellent brazing performance. This study provides a practical technical solution for fabricating highly reliable and high-density lead-free micro-bumps and guides the theoretical development.