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36 DESIGN007 MAGAZINE I MAY 2021 ere are many choices out there and some are better than others at meeting each of these needs. Today, we will explore three of the most common surface finishes—examining how they are applied in manufacturing and looking at the pros and cons of each. Once your board has been processed through solder mask and silkscreen, it is ready for sur- face finish application. At this stage of produc- tion, the PCB is fully functional, at least in theory. e solderable surfaces are copper. In an open environment, an oxidation layer will quickly form, keeping the solder from doing its job. at's why we apply a surface finish like solder, immersion silver, or electroless nickel immersion gold (ENIG) to protect the copper e final surface finish of a PCB is an impor- tant consideration. is coating between your components and the bare board is applied to ensure solderability and protect any exposed copper circuitry. Selecting the right type of surface finish can be daunting, and for good reasons. Designers need to consider whether the selected surface finish will provide an ade- quately reliable solder connection for the application. Is it the best fit for the type of components used in the design? Is it cost effec- tive? Does it meet compliance requirements like the Restriction of Hazardous Substances Directive (RoHS) and the Waste Electrical and Electronic Equipment (WEEE)? A Closer Look at Surface Finish Connect the Dots by Matt Stevenson, SUNSTONE CIRCUITS