The Impact of Hydrogen Gas Evolution on Blister Formation in Electroless Copper Films

Abstract

Electroless copper plating is a key process to provide electrically conductive layers on insulating substrates for the subsequent copper electroplating of printed circuit boards (PCBs). Recently introduced substrate materials are prone to spontaneous delamination failure (blistering) of the electroless layer during deposi-tion. A higher nickel content in electroless copper baths prevents delamination failure by increasing the internal tensile stress in the copper layer. This effect is achieved by suppressing copper self-diffusion through the incorporation of small amounts of nickel in the grain boundaries and the grain boundary junc-tions. Whether the hydrogen gas that evolves inevitably during electroless copper deposition, and that is potentially trapped in the deposit may cause blistering is still under debate. Here we test this hypothesis by quantifying the generated hydrogen gas volume during copper deposition in baths with nickel concentra-tions between 0 and 1000 ppm, and observing the rate of blister formation in the deposit. We find a con-stant molar ratio of 0.65±0.05 mol H2/mol Cu independent of the nickel content in the bath, in contrast to a systematic and substantial change of the blister probability. From this lack of a correlation between the blister rate and hydrogen evolution, we rule out hydrogen evolution as a determining factor for blister for-mation.