Fluxless wetting propeities of one-side-coated under bump metallurgy and top surface metallurgy

Abstract

The wetting balance test was performed in an attempt to estimate the fluxless wetting properties of under bump metallurgy (UBM)-coated Si-wafer and top surface metallurgy (TSM)-coated glass substrate to SnPb solder. The wetting curves of the single-and double-side-coated UBM had a similar shape and the parameters characterizing the curve shape showed a similar tendency as a function of temperature. Wetting property estimation was possible with the new wettability indices from the wetting curves of one side-coated specimens; F_min, F_s, and t_s. Au/Cu/Cr UBM was better than Au/Ni/Ti UBM from the point of wetting time. For TSM, it was more effective to use Cu as a wetting layer with Au as a protection layer than to use Au as a wetting layer alone. The contact angle of one-side-coated Si-plate to SnPb solder can be calculated from the force balance equation by measuring static state force and tilt angle. The contact angles of Au/Cu/Cr and Au/Ni/Ti UBM of Si-wafer to SnPb solder were 59.9° and 63.9°, respectively. The contact angles of Au/Cu/Cr and Au/Cr TSM of glass to SnPb were 78.9 and 76.1°, respectively.