Effects of internal stress of electroless Ni plating on solder joining strength

Nickel/gold electroless plating is commonly used for surface finish of printed circuit boards due to its environmental stability and good solder wettability. However, since deposition of electroless gold plating is a substitution reaction, local corrosion of nickel surface sometimes occurs and it deteriorates joining reliability of solders or wire bonding. In this study, we focused on internal stress of nickel-plating layer. Gold electroless plating was performed on several deferent internal stress level of nickel plating layers, and local corrosion behavior and shear strengths of solder balls were investigated. As a result, it became clear that tensile strength of nickel layer increases occurrence of local corrosion and accordingly it results in deteriorate of solder joining strength.