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76 DESIGN007 MAGAZINE I AUGUST 2020 In recent months, I have encouraged read- ers to take a closer look at conformal coat- ing problems, particularly those that circuit designers could address at the earliest stages of a project. In a recent column, I also offered advice on how to identify some of the poten- tial pitfalls that could sabotage your coating process. In this column, I'm going to look at some issues you are sure to face, from areas of the coated board that simply refuse to cure fully to masking components to the orange peel effect and examining the difference between a critical and a non-critical area of a board. 1. What kills coating quality and cycle time on a typical selective coating line? Selective coating machines deposit a stripe of coating material that can be programmed to stop and start on demand. Stripes of coating can be deposited to create a coating pattern, avoiding areas such as switches, connectors, and test points that must not be coated to pre- vent interference with form, fit, or function. The coating stripes deposited are usually in the 8–1-mm range for optimum accuracy and min- imizing overspray and splashing. When the area to be coated is less than 1 mm in width, then it is necessary to utilise a dispensing step, which is a cycle time killer. Because of the combination of machine X/Y positional accuracy, material fluid dynamics, and component topography, 2–3 mm is usually as close to keep-out areas as anyone would be comfortable coating for a repeatable pro- cess. Must-coat and keep-out areas within 2–3 mm of each other present a problem; again, dispensing will be required—another process step that kills cycle time. How to Overcome Conformal Coating Challenges Sensible Design by Phil Kinner, ELECTROLUBE

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