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64 DESIGN007 MAGAZINE I APRIL 2018 In this, the first of what I hope will become a useful series of "how to" columns on the selec- tion and application of conformal coatings, I'm going to explore why conformal coatings sometimes fail in service and the steps that you can take to avoid failure in the first place. I am a realist. I know that on occasion, con- formal coatings can fail. In this column, I will discuss some of the most common reasons for coating failure. Our investigations at Electrol- ube are thorough, and to list our findings here in any detail is somewhat beyond the scope of this column. However, some of the more com- mon root causes of failure pop up frequently, and for the purposes of my first column, I'd like to run through these issues, offer some tips and dispel the odd myth. As in previous columns, I will present them in our usual Q&A format. What are the reasons for coating failure? Coatings fail for any number of reasons—some common and some uncommon. Here are five fundamental reasons for failure, which are gen- erally the result of poor product selection and/or application, an underlying problem arising from insufficient surface preparation, or some chemi- cal activity going on beneath the coating that is entirely unrelated to the coating chemistry: 1. The coating formulation is simply not tough enough for the job. For example, it fails to maintain an adequate level of insulation when the PCB is subjected to a humid environ- ment and condensation occurs. Many products resist these sorts of conditions and therefore this type of problem can be avoided by making an appropriate material selection at the outset. 2. The coating has not cured properly and therefore hasn't had the opportunity to develop its protective properties to the full. I really can- not emphasise the importance of the applica- tion process and progression to the cure. Get this key element right and you could solve not only this, but a raft of problems in one hit! 3. Poor coverage or insufficient thick- ness. Sharp edge coverage can be difficult to achieve with many coatings, and it can be hard to ensure sufficient thickness in these areas to maintain pro - tection. A combination of material selection and appli- cation technique/workman- ship will remedy these sorts of issues. I'll examine coating thickness a little later in this column. Avoiding Conformal Coating Failures Sensible Design by Phil Kinner, ELECTROLUBE

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