Issue link: https://iconnect007.uberflip.com/i/1531384
Connect the Dots by Matt Stevenson, SUNSTONE CIRCUITS Designing for Reality: Surface Finish In a recent episode of I-Connect007's On the Line with… podcast, we discussed the solder mask and legend process, one of the final steps in the PCB manufacturing process. The board is nearly complete. We just need to wrap up production by applying a surface finish to pro- tect the copper from oxidation and facilitate soldering components onto the board. Copper oxidizes quickly, so all the exposed sol- derable pads are susceptible to oxidation. This can limit the effectiveness of component solder- ing. Applying surface finish to the solder pads will affect solderability during assembly to a limited extent, but today's surface finishes are produced with solderability in mind and are needed to sustain the productive life of the board. Surface Finishes Designers should consider the following when establishing surface selection criteria: • Cost • Restriction of hazardous substances (RoHS) • Flatness of the board surface • Solder joint integrity • Shelf life • Wire bondable (if applicable) With more boards needing to accommodate larger components and more leads over mul- tiple edges or surfaces, flatness becomes one of the more critical manufacturability consid- erations. Surface finish plays a large role in those instances. 62 DESIGN007 MAGAZINE I JANUARY 2025