Effect of Nickel Doping in Sn-Ag-Cu Solders on Intermetallic Compound Formation with Immersion Silver and Copper Surface Finishes

摘要

This study focuses on the doping effect of Ni in Sn-Ag-Cu solder on the intermetallics compound formation during soldering using immersion silver and bare copper surface finish. The O500μm solder alloys consist of Sn-3Ag-0.5Cu, Sn-3Ag-0.5Cu-0.05Ni and Sn-3Ag-0.5Cu-0.lNi were investigated in detail after isothermal ageing at 150℃ for up to 1000 hours. After reflow soldering study, Cu_6Sn_5 was the only reaction product noted for all the different solders used. Reflows using the solder without doping produced a thin and dense layer of Cu_6Sn_5. The addition of Ni into the solder resulted in retarding the excessive growth of Cu_3Sn. In the solid state ageing study, both Cu_6Sn_5 and Cu_3Sn growth had been linked to the formation of micro voids, which in turn increased the potential for a brittle interfacial fracture and thinner Cu,Sn layers might translate into better solder joint strength. Several techniques of materials characterization including optical microscope, image analysis, scanning electron microscopy and energy dispersive X-ray analysis were used to examine and quantify the intermetallics in terms of composition, thickness and morphology.