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66 SMT Magazine • December 2015 What do you do when you need solder mask removed quickly? What do you do when you get the boards back from the shop and there's a miss- ing pad, or your design team did not catch the design error in the pad or trace area, resulting in mask where it's not supposed to be? Perhaps the test group tells you the RF shields need to have the trace opened up in order to pass the testing, but there are literally thousands of boards in the supply chain needing this modification. In these cases solder mask needs to be removed—usually in a hurry—in order to fix these problems. Outside of re-spinning the board and start- ing over, there are several processes that can selectively remove solder mask in a controlled and consistent fashion. Some are better con- trolled than others and include mechanical abrasion, chemical etching, and micro and la- ser ablation. Several factors will help determine the meth- od to use including the type of solder mask, and where the area of interest is located. Other fac- tors are the quantity of PCBs, the amount of solder mask needing removal and whether the circuit boards are bare boards or are populated with components. Grinding and Scraping One of the most straightforward methods of mask removal is via scraping or grinding of the soldermask (Figure 1). Since solder mask is only a little more than 1mil in thickness it does not by bob Wettermann BEST inC. KnocKInG DoWn THe bone PILe no Time for a board Spin? Selective Solder mask removal ColuMn Figure 1: Selective manual scraping of solder mask.

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