Solder metallization interdiffusion in microelectronic interconnects

We investigated the growth of intermetallic compounds in Cu/Ni/Au/PbSn sold er joints. The substrates that we investigated had been Au plated by one of two different techniques, The An finish thicknesses ranged from 0.25 to 2. 6 mu m. After solder reflow, structural examinations using optical and elec tron microscopy of cross-sectioned solder joints revealed the growth of Ni3 Sn4 at the solder/Ni interface after reflow. Solder joints with thicker lay ers of An annealed in Ar gas at a temperature of 150 degrees C for up to 45 0 h, displayed an appreciable growth of Au0.5Ni0.5Sn4 at the Ni3Sn4/solder interface. Previous investigators correlated growth of a Au-Sn alloy with t he degradation of the mechanical properties of the solder joint. The determ ination of the stoichiometry of the Au0.5Ni0.5Sn4 phase provides some under standing of why this phase grew at the Ni3Sn4/solder interface, as Sn, Au a nd Ni are all readily available at this interface. The growth of this terna ry alloy is also consistent with trends observed in the kinetics of formati on of solder alloys.