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60 DESIGN007 MAGAZINE I DECEMBER 2021 Today's PCBs increasingly must operate in challenging conditions. Whether it's an iPad hot to the touch aer several hours of gaming or a drone slicing through smoke and debris to monitor a wildfire, boards need protection from the elements. at's where solder mask comes in. Solder mask isn't just the stuff that makes PCBs green and protects the copper from the elements; it is an increasingly vital part of boards that have to do more in less hospitable environments. Solder mask coats your whole board (apart from the solder pads) so the PCB doesn't react with the atmosphere and lose chemical properties through oxidation. It also prevents contamination from dust and debris that may settle on the board and create shorts. Solder mask prevents bridging between features during wave reflow assembly, limits external Best Practices for Solder Mask Application conductive influences, and helps ward off voltage spikes. Don't Skimp on Solder Mask Some board fabrication houses offer reduced prices if you order your boards without solder mask and that can work for some designs, but not always. If you choose to use a stencil to apply solder paste and run the board through a reflow oven, the solder will spread back on the exposed copper traces. is may leave your parts without enough solder on the pins to cre- ate a reliable connection or, worse yet, bridge adjacent conductors creating shorts. Solder mask will increase reliability and reduce cost in the long run. All in all, solder mask is a critical element when it comes to sustained performance. How it gets on the PCB matters, making it Connect the Dots by Matt Stevenson, SUNSTONE CIRCUITS