Development of a Quick Test for Conformal Coatings

Abstract

Conformal coatings are applied to protect printed circuit boards and components mounted on them from the deleterious effects of moisture, particulate matter and corrosive gases. The conventional method of testing the effectiveness of these coatings is to expose the conformally coated hardware to a corrosive environment for extended periods of time — often lasting many months — and determine the mean time to failure. iNEMI’s Conformal Coating Evaluation for Improved Environmental Protection project team is recommending a quicker test method that takes less than a week to evaluate conformal coatings. This method uses the corrosion rates of conformally coated thin films of copper and silver exposed to a sulfur gas environment as a measure if the coating performance. The project team investigated how temperature and humidity impact the corrosion rates of conformally coated copper and silver thin films compared to uncoated films. Performances of acrylic, silicone and atomic layer deposited (ALD) coatings were studied as a function of temperature and relative humidity. The team found that temperature affected the corrosion rates of conformally coated copper and silver thin films, whereas relative humidity had a lesser influence. The team also discovered significant differences in corrosion protection provided by the three coatings that were tested.