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72 PCB007 MAGAZINE I MARCH 2025 tion loss. e right choice of surface finishes is paramount for signal integ- rity and overall reliability of elec- tronic assemblies. e novel surface finish with nano-engineered barrier layer— finished with an outermost gold layer—has shown superior bene- fits in 5G-mmWave frequency PCB technologies. e technical evalu- ation of signal integrity at 5G-high band, mmWave and higher frequen- cies with novel surface finish com- paring with alternatives will be dis- cussed. Furthermore, reliability eval- uation will be highlighted involving this novel surface finish. Introduction With the tremendous growth of mobile phones/devices, the availability of internet, and hand-held/wearable devices, the amount of information transfer occur- ring on wireless networks has increased enor- mously. In order to transfer the amount of data required by today's standards, electronic device manufacturers utilize high-speed, high- frequency electronic signals. e integrity of high-frequency signals can be affected by the choice of materials used to fabricate printed circuit board (PCB) assemblies in receiving Table 1: Skin depth relationship with frequency (GHz). Figure 1: Insertion loss comparison between circuits with bare copper conductors and with ENIG-plated copper conductors, from 0–50 GHz 3 . devices. e combination of high-frequency signals with small geometry conductive traces (e.g., wearable devices, etc.) can lead to signal losses and compromised performance. e primary factor which affects the integ- rity of high-frequency signals is conductor loss, mainly affected by the surface finish applied on the copper pads of PCBs 1,2 . Among the sur- face finishes available for these applications, electroless nickel immersion gold (ENIG) sur- face finish has been a popular choice. How- ever, ENIG can lead to an increase in inser- tion loss due to the presence of nickel (sche- matic Figure 4, and graph Figure 1). Nickel has one-third the conductance of copper, leading to higher conductor losses 3 . Also, the nickel- phosphorous (Ni-P) layer has ferromagnetic properties which adversely affect the circuit performance 4 . As the frequency increases, the current den- sity is concentrated towards the surface (sur- face finish) instead of the entire Cu cross-sec- tion (Table 1). Hence the choice of surface fin- ish is critical since it will affect the insertion loss. Figure 1 shows increased insertion loss due to ENIG surface finish on copper