| The wetting balance method was used to estimate the fluxless wetting properties of UBM-coated Si-wafer to the binary lead-free solders(SnAg, SnSb, SnIn, SnBi, SnZn). The wetting property estimation of UBM-coated Si-wafer was possible with the new wettability indices from the wetting curves of one side coated specimen; F_(min), F_s, and t_s . For UBM of Si-chip, Au/Cu/Cr UBM is better than Au/Ni/Ti in the paint of wetting time. At general reflow process temperature, the wettability of high melting point solders(SnSb, SnAg) is better than that of low melting point ones(SnBi, SnIn). The nitrogen atmosphere made more significant improvement in fluxless wettability than in fluxed wettability. The contact angle of the one side-coated Si-plate to the solder could be calculated from the force balance equation by measuring the static state force and the tilt angle. |
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