Development of Cost-Effective Ni-Less Surface Finishing Process for High-Speed PCBs

The growing need to use low-power and high-frequency signals for the high-speed transmission of large-capacity data is driving the demand for suitable printed circuit boards. Most printed circuit boards use Cu as a conducting material and require a surface finish that forms an organic or a metallic protective layer on the Cu surface to prevent Cu diffusion/oxidation. Metallic protective layers typically have a higher resistivity than Cu, resulting in significant signal transmission losses in the high-frequency range. For example, electroless Ni/electroless Pd/immersion Au (ENEPIG), a surface finish that forms a metallic protective layer, sequentially forms Ni-P, Pd-P, and Au layers on a Cu surface. Among these, the Ni-P layer is the main cause of signal transmission loss owing to its high resistivity. In this study, we developed immersion Ag/immersion Pd/immersion Au (ISIPIG), a cost-effective surface finishing process that does not form a Ni-P layer. ISIPIG effectively prevented the diffusion/oxidation of Cu and improved solder wettability while exhibiting a lower insertion loss and higher antenna efficiency than ENEPIG. Our results suggest that ISIPIG is a promising surface finishing process for applications that require the high-speed transmission of large-capacity data using low-power and high-frequency signals.