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66 The PCB Magazine • September 2015 by Tara Dunn omni PcB flex talk Final Surface Finishes for Automotive: No One-Size-Fits-All Solution FEAturE Column The predominant surface finishes being specified for automotive electronics—one of the fastest growing electronics market segments— are immersion silver, OSP, and immersion tin. Each is selected to meet critical application de- mands. Remember the good ol' days when hot air solder leveling was the go-to surface finish for almost all applications? The decision about sur- face finish was an easy one. The primary func- tion of the surface finish was to protect the copper from oxidation prior to assembly. Wow, have things changed! Today's expectations in- clude: superior solderability, contact perfor- mance, wire bondability, corrosion and thermal resistance, extended end-use life, and of course, all at a low cost. Common surface finishes now include HASL, both leaded and lead-free, OSP, immersion tin, immersion silver, ENIG and EN- EPIG. Unfortunately, there is no one-size-fits-all surface finish that fulfills all the requirements in the industry; the decision really depends on your specific application and design. With over 100 different PCBs in a typical vehicle and de- signs ranging from heavy copper, rigid boards to flexible circuits, automotive electronics clear- ly demonstrates the need to utilize multiple sur- face finish options. Recently, Elizabeth Foradori and I sat down with OEM/Assembly Specialist Robyn Hanson of MacDermid Electronic Solutions to learn about the key considerations for final surface finish choice and the cautions of each from the OEM or assembly perspective. To listen to the discussion, click here. For a concise list of the pros and cons of each finish, click here. Follow- ing are some of the highlights. Considerations for Surface Finish Choice: Does the application require lead or lead-free assembly? Will the end environ- ment have extreme temperatures or humidity concerns? What shelf life is needed, and will it be months or years? Does the design have fine-pitch components? Is this an RF or high- frequency application? Will probeability be re- quired for testing? Is thermal resistance or shock and drop resistance required? Once these questions are answered, the sur- face finish options can be reviewed to find the best fit.

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