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

The effect of a reflow process and under bump metallurgy (UBM) systems on the growth of intermetallic compounds for Sn/Bi and Pb/Sn solder bump/UBM interfaces was investigated. The UBM systems were sputtered Al/Ti/Cu, Al/Ti/electroless plated Cu, Al/NiV/sputtered Cu, Al/electroless plated Ni/Au, and the solder bumps were eutectic Pb/Sn and Bi/Sn fabricated by an electroplating method. Microstructure and composition of intermetallic compound (IMC) phases and their morphology were examined using scanning electron microscopy and X-ray diffraction. The IMC compounds were confirmed to be Cu/sub 6/Sn/sub 5/, Cu/sub 3/Sn, Ni/sub 3/Sn/sub 4/, or Ni/sub 3/Sn depending on UBM and solder types. The effect of IMC growth on bump adhesion strength was also investigated using a ball shear test. It turns out that ball shear strengths of the systems depends not on processing conditions but on solder/UBM interfacial adhesion strength.