This work presents device level testing of a lead free soldered electronic device tested with bias on under cyclic humidity conditions in a climatic chamber. Besides severe temperature and humidity during testing some devices were deliberately contaminated before testing. Contaminants investigated are ionic or airborne contaminants likely to be introduced by production or service conditions. The effect of changes in processing parameters as a result of production shift to lead free solder (e.g. higher soldering temperature) has also been investigated. Analysis have shown that one printed circuit board assembly (PCBA) in the device is more prone to corrosion reliability and this was further analysed using thermography to detect areas that have high risk of condensation due to lower temperature under working condition. Tested PCBAs are subjected to detailed investigation before and after testing using high resolution photography, detailed optical microscopy and SEM/EDS.
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 processrelated 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.
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