The Role of Permeability and Ion Transport: In Conformal Coating Protection

摘要

The level of protection offered by a range of conformal coatings on electronic assemblies has been evaluated. The role of permeability and ion transport is the primary interest. Testing was carried out on 6 coatings of the main generic types currently used by industry either conformally coated onto FR-4 laminate boards or, as free films. The coatings were evaluated in terms of the degradation caused by sodium chloride and a generic flux formulation based on dibasic acids. The methods utilised were surface insulation resistance (SIR), sequential electrochemical reduction analysis (SERA), PermeGear diffusion cells and gas chromatography mass spectrometry (GC-MS). Conformally coated boards were used for the SIR and SERA measurements while free films of the selected coatings were used for the diffusion and GC-MS measurements. Each method revealed aspects of the level of protection offered by the coatings as well as the extent to which the coatings are permeable to contaminants in high environmental stress regimes. The coatings acted as an effective barrier to NaCl penetration but were permeable to dibasic acids found in electronic fluxes. The importance of board cleanliness is also highlighted by the results obtained from these investigations.