Investigations of wetting properties of Ni–V and Ni–Co alloys by Sn, Sn–Pb, Sn–Cu, and Sn–Ag–Cu solders

Wetting properties of the Ni–7 wt%V and Ni–Co alloys by Sn, Sn–Pb, Sn–Cu, and Sn–Ag–Cu solders are determined using the wetting balance technique. The Ni–7 wt%V alloy is the most commonly used diffusion barrier layer material of flip chip packaging. Ni–Co alloys are the potential alternative diffusion barrier layer materials for flip chip packaging of Cu/low k chips. A statistical approach is used to analyze the relative importance to the wetting properties of each factor such as solder, substrate, flux, and their interactions. By substrates, the ranking of the wetting properties is Ni > Ni–Co > Ni–7 wt%V. For substrates, the most important factor to the wetting properties is the solder. By solders, the ranking of the wetting properties is Sn–37 wt%Pb > Sn > Sn–3.0 wt%Ag–0.5 wt%Cu > Sn–0.7 wt%Cu. For Sn–0.7 wt%Cu and Sn–3.0 wt%Ag–0.5 wt%Cu solders, the most important factor to the wetting properties is the flux. Development of flux is crucial to Pb-free solders. Wetting properties of Ni–Co alloys do not exhibit significant dependence upon the Co additions.