Industrial & Engineering Chemistry Research, Vol.53, No.8, 3097-3104, 2014
Investigation on Circular Plating Pit of Electroless Ni-P Coating
In this study, a typical circular pit of electroless Ni-P coating has been investigated with atomic force microscopy (AFM), nanoindentation, and focused ion beam-scanning electron microscopy (FIB-SEM). It is found that the land area of the circular pit has lower hardness than the good surface, and there is a spherical-crown-shaped boundary between the pit and the coating. The formation mechanism of such defects is because the H-2 gas bubble generated by the chemical reaction attaches to the plating surface and stops the Ni-P growth on such area, and after the bubble is released the Ni-P starts to grow again and forms a new germination phase. The computational fluid dynamics (CFD) simulations have found that the plating fluid with current plating carousel design has vortex flow around the disks and the H-2 gas bubbles have a high possibility to attach to the disk surface. An optimized plating carousel design is proposed which can facilitate the release of H-2 gas and reduce such circular pits.