Effects of Bath Composition and P Contents on the Defects of NiP Layer in Electroless Nickel Immersion Gold Process

Electroless nickel immersion gold (ENIG) has been widely used for surface finishing in PCB industry, however surface defects are sometimes found during PCB soldering process. These defects cause failures in soldering on PCB and consequently cause poor safety probability of products. The formation mechanism of the defects in the NiP layer was investigated. Three parameters on the black pads were analyzed. First, morphology was analyzed with changing metal turn over (MTO) numbers. Second, pH of Ni solution was changed in the ENIG process. Third, stress of NiP layers was analyzed at different pH. The relationship between each defect and P contents was analyzed. High open circuit voltage (OCV) can cause the poor surface morphologies as well as the defects. High and large difference of P contents in NiP layer can act the important role in the formation of black pads. The high tensile stress can also be another factor of the formation of black pads.