IPC 4556

This specification sets the requirements for the use of electroless nickel/electroless palladium/immersion gold (ENEPIG) as a surface finish for printed boards. It establishes requirements for ENEPIG deposit thicknesses for applications including soldering, wire bonding and as a contact finish. It is intended for use by chemical suppliers, printed board manufacturers, electronics manufacturing services (EMS) providers and original equipment manufacturers (OEMs). ENEPIG is a tertiary layered surface finish plated over copper as the basis metal. ENEPIG is a multifunctional surface finish, applicable to soldering and to gold, aluminum and copper wire bonding. It is also suitable as the mating surface for soft membrane and steel dome contacts. Additional applications include use in low insertion force (LIF) and zero insertion force (ZIF) edge connectors and for press-fit applications. The electroless palladium layer forms a diffusion barrier that impedes nickel diffusion to the gold surface and, in turn, the immersion gold protects the palladium layer from reacting with contaminants prior to processing that might otherwise affect joining processes, such as wire bonding and soldering.