Electroplated Ni-P film for power devices without cracks induced by high temperature heating

Abstract

The cracks induced by high temperature solder joint in Ni-P film are one of the important reliability issues in power devices for automobiles. In this study, we focused on the P concentration and investigated the Ni-P film without cracks induced by high temperature heating. The low-P (1–2 wt%), the medium-P (8–9 wt%) and high-P (13–14 wt%) Ni films were formed on an Al substrate by electroplating using a Watt bath. The medium-P and high-P Ni films underwent a phase transition to a Ni-P compound mainly composed of Ni3P by heat treatments at 380–400 °C and a thermomechanical analysis revealed the shrinkage of the films. In addition, cracks were induced at the films when they were pressed into by a Vickers indenter. In contrast, cracks were not induced in the low-P (<1.67 wt%) Ni film even after the heat treatment. This is probably because a large strain generated between the underlayer Al substrate and the Ni-P film by thermally expansion causes cracks. The low-P Ni film should achieve a power device that avoids crack generation and with high reliability.