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44 PCB007 MAGAZINE I OCTOBER 2022 Surface finish is a critical component in PCB design and functionality. Surface finishes form the interface between the component and the circuitry. As its most essential function, the final finish process is intended to provide exposed copper circuitry with a protective coating to preserve solderability. Select sur- face finishes are also used for wire bonding or as an electrical contacting surface. Perhaps no other step in the PCB manufacturing process has undergone more change in the era of sur- face mount manufacturing than the final finish chemical process. Electrical signals are transmitted through copper circuitry connecting the different com- ponents throughout the finished board. Cop- per is a highly conductive metal but one of its shortcomings is that it oxidizes when exposed to ambient air. An oxidized copper surface will Surface Finish Evolution from Conventional to Advanced not solder and is a poor conductor with no possibility of wire-bonding. Surface finish is applied to ensure no exposed copper is in the final product. Soldering, wire bonding, and contacting are all made with the finished sur- face. Today there is a wide variety of finishes that board designers can specify to meet the desired functionality and intended use of their circuit boards: • A reliable solder joint with leaded and lead-free solder interface • Bonding surface Al, Au, Cu, Cu/Pd • Contacting surface insertion • A finish that will not impede RF signal transmission When soldering of through-holes was the only desired attribute, three SFs dominated The Plating Forum by George Milad, UYEMURA

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