Hydrogen evolution and thermal treatments for removal of plating induced impurities from Ni to extend life of solder joints

Abstract

As operating temperatures and times continue to increase for solder joints with Ni pads, large voids inevitably form at the intermetallic compound (IMC) – solder interface when the IMC thickness nears 5 μm. This leads to a significant reduction of strength, thermal conductivity, and fatigue resistance, and in small joints, also to electromigration life degradation. We have identified the voiding root cause as the breakdown and subsequent outgassing of deposition-related Ni-oxo-hydroxide impurities, impractical to avoid during Ni commercial electroplating. This work takes as the starting point a successful post-deposition voiding-mitigation treatment with 24-hour annealing at 450 °C. It then explores the possibility of rendering this routine more practical by lowering the annealing temperature down to 250 °C. While that approach shows relatively limited success, an alternative strategy, involving treatment with hydrogen evolution reaction for one hour at room temperature, alone or in combination with thermal, leads to a substantial reduction in the voiding propensity.