Correlation between Ni3Sn4 intermetallics and Ni3P due to solder reaction-assisted crystallization of electroless Ni–P metallization in advanced packages

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Abstract
Ni3Sn4 intermetallic was formed by the depletion of Ni from electroless Ni–P, and a Ni3P layer was formed simultaneously due to solder reaction-assisted crystallization during solder reflow. Both Ni3Sn4 and Ni3P grew rapidly due to the solder reaction-assisted crystallization and their growth was diffusion controlled during the first 15 min of annealing at 220 °C. After that, the growth rate of Ni3Sn4 was greatly reduced and the crystallization of electroless Ni–P to Ni3P was no longer induced. Based on kinetic data and scanning electron microscope morphology observations, underlying mechanisms causing this specific phenomenon are proposed. This finding is indeed very crucial since we may control the growth of Ni–Sn intermetallics by monitoring the solder reaction-assisted crystallization of electroless Ni–P.