Conformal coating thickness determination: A comparison of methods

In the manufacture of electrical and electronic packages and assemblies, conformal coatings are employed to protect the electronic package from moisture, gases, and other constituents of harsh atmospheres. In addition, circuit board dielectric characteristics can be improved by proper use of conformal coatings. The actual product use and design requirements will normally dictate the method of coating application and cured thickness needed. In any case, some method of thickness measurement is desirable from both a quality control standpoint as well as operator "during-the-fact" testing. This paper discusses several alternative methods of measuring the thickness of cured conformal coatings. More familiar methods are reviewed and put in perspective by a subsequent discussion of a more recent non-destructive technique. A statistical analysis of the data is included.