Flip Chip Bump Formation of Sn–1.8Bi–0.8Cu–0.6In Solder by Stencil Printing

Flip chip bumping by stencil printing method using a new composition of solder paste, Sn–1.8%Bi–0.8%Cu–0.6%In, all in mass%, was investigated. Sn–3.5%Ag, Sn–37%Pb and Sn–36%Pb–2%Ag were selected as references for the experiment. The solder pastes were printed on the under bump metallization (UBM) of a Si-wafer using a stencil, where diameter and thickness of the stencil opening were 400 and 150 μm, respectively. The UBM deposit comprised 0.4 μm …