Comparison of electroplated eutectic Bi/Sn and Pb/Sn solder bumps on various UBM systems

Abstract

The effect of a reflow process and under bump metallurgy (UBM) systems on the growth of intermetallic compounds (IMC) of the 57Bi/43Sn and 37Pb/63Sn solder bump/UBM interfaces was investigated. The selected UBM systems were sputtered Al/Ti/Cu, sputtered Al/NiV/Cu, Al/electroless Ni/immersion Au, and Al/Ti/electroless Cu. An alloy electroplating method was used for the solder bumping process. The microstructure and composition of intermetallic compound (IMC) phases and their morphologies were examined using scanning electron microscopy and X-ray diffraction. The Cu/sub 6/Sn/sub 5/ /spl eta/'-phase IMC appeared on all Cu containing UBM cases with Pb/Sn and Bi/Sn solders and the Cu/sub 3/Sn /spl epsiv/-phase was detected only with Pb/Sn solder bumps. The Ni/sub 3/Sn/sub 4/ IMC was found to be the main IMC phase between Ni and solder. The Ni/sub 3/Sn secondary IMC was also detected on the electroless Ni UBM with PbSn solder after ten times reflow. Through the bump shear test, Al/NiV/Cu, Al/elNi/Au, and Al/Ti/elCu UBMs showed good stability with Bi/Sn and Pb/Sn solder in terms of metallurgical aspects.