Contamination on electronic assemblies can impact conformal coating performance, leading to moisture entrapment, poor adhesion, and improper curing. These issues can lead to coating failure and eventually to failure of the PCBA due to electrochemical migration, delamination, and insufficient environmental protection.
Different contaminants contribute to specific defects—hygroscopic residues trap moisture, organic residues affects adhesion, and ionic contamination interfere with curing.
To assess cleanliness before coating, methods like ROSE testing, ionic chromatography, surface energy measurement, FTIR, and microscopy are used. Zestron Europe conducted a study to showcase the effect of different contaminants on coating in comparation to a clean board. The study has shown larger defect size and defect density on uncleaned boards. Additional defect analysis techniques, including the iodine vapor test, CoRe test, and liquid indicator coating layer test are demonstrated on these boards showing the abilities and best applications for these methods. In addition an overview of the methods and their representation in industry standards is provided.
