Effect of Ni additive on electroless Cu quality for high density interconnect PCB substrate

Microvias play a key role in the high density interconnect (HDI) printed circuit board (PCB) substrate, which provides electrical interconnect among build-up layers. To achieve a high quality microvia structure, a flawless electroless Cu seed layer is necessary. In this work, we investigated the nanovoids in the electroless layer caused by hydrogen bubbles and explore the effect of Ni additive on the nanovoid generation. It is found that a high Ni concentration can increase Cu reaction speed and nano-voiding phenomena in terms of size and numbers. This might be due to the high Cu reaction speed leading to the hydrogen bubbles have a few time to escape from the Cu surface and then getting trapped in the deposition layer.