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50 DESIGN007 MAGAZINE I JUNE 2023 Article by Frank Xu, PhD and Martin Bunce, MACDERMID ALPHA, and John Coonrod, ROGERS CORPORATION Introduction Over the years, various surface finishes have been successfully utilized, namely organic sol- derability preservative (OSP), immersion sil- ver (ImAg), immersion tin (ImSn), electroless nickel immersion gold (ENIG), and electroless nickel electroless palladium immersion gold (ENEPIG), as solderable finishes for PCB and package substrates. All these surface finishes have their pros and cons, with no single finish being suited to all applications. As system designers continue to respond to new performance demands, it can be noted that ENIG/ENEPIG finishes have endured as a leading choice in many advanced applications where reliability is prioritized over cost. Electroless nickel (EN) deposits have served well as a barrier layer, preventing copper migration to the outer gold or palladium-gold surfaces, and enabling the robust solderability performance of ENIG and ENEPIG finishes. However, the introduction of the 5G mobile network creates a growing demand for smart- phones, networking, and wireless connections, all requiring increased "data flow." e need to reduce the signal loss at higher frequency bandwidth is becoming vitally important. e low conductivity and magnetic properties of EN affect electrical signals as they travel along a conductor's outer surfaces leading to inser- tion losses at higher frequencies. Reassessing Surface Finish Performance for Next-generation Technology, Part 1

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