Amorphous Pd layer as a highly effective oxidation barrier for surface finish of electronic terminals

The oxidation resistance of two important surface finishes, electroless Ni/immersion Au (ENIG) and electroless Ni/electroless Pd/immersion Au (ENEPIG), is studied. Auger electron spectroscopy and X-ray photoelectron spectroscopy analyses show that ENEPIG is more oxidation resistant. The oxidized species of Ni diffuse through the Au grain boundaries. The mechanism for this better performance is that the Pd layer has an amorphous structure. The amorphous Pd layer is able to inhibit the out-diffusion of Ni atoms through high-diffusivity paths.