The UK’s National Physical Laboratory (NPL) has launched its latest report, "Test Method for Conformal Coating Protection Performance of Electronic Assemblies in Harsh Environments." The report describes new developments in a test method for assessing conformal coating protection performance on electronic assemblies using the surface insulation resistance (SIR) technique.

The UK’s National Physical Laboratory (NPL) has launched its latest report, "Test Method for Conformal Coating Protection Performance of Electronic Assemblies in Harsh Environments." The report describes new developments in a test method for assessing conformal coating protection performance on electronic assemblies using the surface insulation resistance (SIR) technique. The new method is significantly different than the existing standard in a number of respects and reflects a more realistic application of conformal coatings.

In the study, the method was used to investigate the protection performance of seven different types of coatings (two water-based acrylics, solvent-based acrylic, fluoroacrylate, silicone, polyurethane, and epoxy) against solvent-based flux, surfactant and SO2 gas. The results demonstrated that the SIR technique is a suitable discriminatory tool for assessing coating performance and is sensitive in detecting the circuit reliability underneath coatings. The coating type affects the level of protection against specific contaminants; i.e., coatings are contaminant-sensitive. Coating protection performance is not only dependent on the coating and contaminant type, but also on the component type where shape factor and coating coverage is an issue. Therefore, the results on protection performance of conformal coatings using this new test method and test board design provide more realistic and useful information on the protection performance of conformal coatings against the harsh environment in which electronic circuits operate.

For more information, e-mail Dr. Chris Hunt at chris.hunt@npl.co.uk or visit www.npl.co.uk.