Effect of solder flux residue on the performance of silicone conformal coatings on printed circuit board assemblies

Abstract

Conformal coatings are applied on printed circuit board assemblies (PCBAs) in order to protect the assembly from environmental influence and silicone-based coating is commonly used. A systematic study on the performance of silicone conformal coating in connection with process-related contaminants is the focus of this paper. Different test substrates such as plain laminate surface and a test PCBA with and without conformal coatings were exposed to high humid environment at ambient temperature and the performance of the coating was evaluated using various parameters such as increase in leakage current across the components, morphology of the coating, and analysis of dendrite formation due to electrochemical migration under the coating. The morphology of the coating before and after exposure was investigated using scanning electron microscopy, and energy dispersive X-ray spectroscopy. Results show that the presence of flux residues greatly influences the electrical functionality of the components and also degrades the performance of the coatings compared to the clean substrates.

Keywords:

• Conformal coating
• Silicone
• No-clean flux residue
• Blisters
• Coating failure
• Electrochemical migration