A study on reliability of UBM systems for LF-CSP package

In the case of UBM (Under Bump Metallurgy) system for LF-CSP package, bare Cu, Cu/Ag, Cu/Ni/Ag, Cu/Ni/Pd and Cu/Pb-Sn systems were investigated. As th e results of bah shear strength test after various environmental test, Cu/S n-10Pb system showed the highest shear strength value. To block the diffusi on of Cu and minimize the formation and growth of IMC, Ni layer added on Cu alloy. Thus we selected the Cu/Ni/Sn-10Pb system as the UBM type in our st udy. In order to evaluate the solder joint strength, samples were prepared as a function of number of reflow and high temperature storage at various t ime. After each tests, microstructure and fracture surface were analyzed wi th optical microscope, SEM, XRD and EDX to study the interfacial reaction a nd the fracture mechanism.