Measuring Conformal Coating Thickness
Typical dry film thicknesses of conformal coatings range from 1 – 5 mils (25.4 – 127μm) and can be verified using the following techniques:
Micrometer – A simple non-destructive method is to measure points along the uncoated substrate with calibrated micrometers then re-measures these points afterwards, with the difference being the coating thickness.
Positector – A less cumbersome, non-destructive technique employs a digital coating thickness gauge which measures changes in either magnetic or electric fields to determine film thickness. While this technique is much quicker and easier, it is limited to use on conductive substrates, and therefore cannot measure coating thicknesses over solder mask or other insulated components.
Micro-Section Analysis – The easiest non-destructive tool to use when measuring coating thickness is a wet film gauge with a black lamp. However, this method can only be applied with high solids systems, such as UV coatings. Finally, for highly accurate coating thickness measurements, cross-section analysis can be applied in which a section of the coated substrate is cut out and mounted in a plastic mold. The cross section is then polished and analyzed under a powerful microscope to measure the coating thickness at different points. While this technique provides the most accurate measurements, it requires much time and costly equipment, and destroys the sample.
Rework / Repair – Occasionally, repairs are required to touch up areas where coating has become damaged, delaminated, or otherwise removed from the substrate. This typically occurs over a very small area that requires precise application. Therefore, these repairs are typically applied by brush to localize and confine the reapplied coating to a small area.