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54 SMT007 MAGAZINE I MAY 2018 Masking of printed circuit boards post rework/repair as well as for initial PCB assem- bly is often required if the PCB is to be confor- mal coated. If a board that has conformal coat- ing on it needs to be reworked or repaired, the conformal coating needs to first be removed before the operation of rework or repair can take place. Once the board has been inspected, tested and cleaned, the conformal coating needs to be re-applied to the area of rework or repair. A conformal coating keep-out area drawing is essential in determining which components require masking. The following discussion centers around the various options for conformal coating masking via a liquid application process. For purposes of this discussion, rework is defined as the removal and replacement of a component to meet initial specifications and performance characteristics of the board. Repair is defined as restoration of physical damage done to a PCB that brings the board back to functionally but may not meet the orig- inal performance intentions. Parylene masking and de-masking is not part of this discussion. There are numerous options available for conformal coating masking. The most common methods for masking off or protecting select areas of the PCB or components themselves are the following: • Precut tape dots • Laser-cut custom tape shape • Tape that is hand cut and trimmed to size • Liquid latex • Silicone boots • 3D printed custom shapes Knocking Down the Bone Pile by Bob Wettermann, BEST INC. Masking of Conformal Coating During Assembly and Rework

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