Reliable Nickel-Free Surface Finish Solution for High-Frequency, HDI PCB Applications

Abstract

Abstract The evolution of Internet-enabled mobile devices has driven innovation in the manufacturing and design of technology capable of high-frequency electronic signal transfer. Among the primary factors affecting the integrity of high-frequency signals is the surface finish applied on printed circuit board copper pads—a need commonly met through the electroless nickel immersion gold process (ENIG). However, there are well-documented limitations of ENIG due to the presence of nickel, the properties of which result in an overall reduced performance in the high-frequency data transfer rate for ENIG-applied electronics, compared with bare copper. An innovation over traditional ENIG is a nickel-less approach involving a special nano-engineered barrier designed to coat copper contacts, finished with an outermost gold layer. In this study, assemblies involving this nickel-less novel surface finish have been subjected to extended thermal exposure, then intermetallics analyses, contact resistance comparison after every reflow cycle (up to six reflow cycles) to assess the prevention of copper atom diffusion into the gold layer, solder ball pull and shear tests to evaluate the aging and long-term reliability of solder joints, and insertion loss testing to gauge whether this surface finish can be used for high-frequency, high-density interconnect applications.