Significant consumption of Ni-P layer in Ni-P/Sn-0.7Cu solder joints during thermomigration

Thermomigration is atomic diffusion driven by a temperature gradient in binary alloys and its effect in solder joints at 200 °C for SiC power modules is still unclear. This study investigates the effect of thermomigration on microstructural evolution in Ni-P/Sn-0.7Cu/Ni-P solder joints under a relatively low-temperature gradient (628 °C/cm) at 200 °C. The Ni-P layer at the hot side was remarkably consumed in regions with a low angle between the c-axis of β-Sn and the temperature gradient at 200 °C. On the contrary, no consumption of the Ni-P layer was detected without the temperature gradient at 200 °C. These results indicated that thermomigration of Ni occurred under a temperature gradient of only 628 °C/cm at 200 °C in these regions. We propose that the thermomigration of Ni in Ni-P/Sn solder joints could significantly affect the reliability of SiC power modules.