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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 demands.
Remember the good ol’ days when hot air solder leveling was the go-to surface finish for almost all applications? The decision about surface finish was an easy one. The primary function of the surface finish was to protect the copper from oxidation prior to assembly. Wow, have things changed! Today’s expectations include: superior solderability, contact performance, 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 ENEPIG. 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 designs ranging from heavy copper, rigid boards
to flexible circuits, automotive electronics clearly demonstrates the need to utilize multiple surface 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. Following are some of the highlights.
Considerations for Surface Finish Choice: Does the application require lead or lead-free assembly? Will the end environment 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 highfrequency application? Will probeability be required for testing? Is thermal resistance or shock and drop resistance required?
Once these questions are answered, the surface finish options can be reviewed to find the best fit.
Editor's note: This aticle originally appeared in the September 2015 issue of The PCB Magazine.