Wettability and interfacial reactions between the molten Sn–3.0 wt%Ag–0.5 wt%Cu solder (SAC305) and Ni–Co alloys

This study examines the wetting properties and interfacial reactions between molten Sn–3.0 wt%Ag–0.5 wt%Cu solder and Ni–Co alloys to evaluate Ni–Co alloys as alternative diffusion barrier layer materials in flip chip packaging for Cu/low k integrated circuits. The wetting properties of Ni–Co alloys with Sn–3.0 wt%Ag–0.5 wt%Cu solder are better than the currently used Ni–7 wt%V. With increased Co, the surface roughness of Ni–Co alloys increase and the wetting properties decrease. The Co effects on Sn–3.0 wt%Ag–0.5 wt%Cu/Ni–Co interfacial reactions are verified. The Sn–Ni–Co isothermal section illustrates the reaction paths. As Co increases from 10 to 40 at%, the reaction path shifts from the Sn–Ni side towards the Sn–Co side. The reaction rates in the different reaction couples are determined. The Ni–10 at%Co has the lowest reaction rate with the Sn–3.0 wt%Ag–0.5 wt%Cu solder.

Research highlights▶ Wetting properties of Ni–Co alloys are better than the currently used Ni–7 wt%V. ▶ With increased Co, the wetting properties of Ni–Co alloys decrease. ▶ SAC305/Ni–Co interfacial reactions depend on Co additions. ▶ When the Co addition to 20 at%, the Co effect is comparable to that of Cu.