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| Typical Corrosion and Protection Measures Against Airborne Contaminants on Circuit Boards |
| Received:March 11, 2019 Revised:July 25, 2019 |
| View Full Text View/Add Comment Download reader |
| DOI：10.7643/ issn.1672-9242.2019.07.015 |
| KeyWord:printed circuit board assembly airborne contaminants failure analysis protective coatings salt mist test |
| Author | Institution |
| TANG Jun |
Casco Signal Ltd, Shanghai , China |
| WANG Yong |
Casco Signal Ltd, Shanghai , China |
| JING Peng-yuan |
Casco Signal Ltd, Shanghai , China |
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| Abstract: |
| Objective To solve corrosion failure of printed circuit board assembly (PCBA) caused by atmospheric contami-nation and improve the adaptive capacity of PCBA in environment of atmospheric contamination. Methods Two typical corrosion failure examples were selected in combination with thick-film resistor and SMD LED from the perspective of device selection. The morphology of corrosion was analyzed with metallographic microscopic and scanning electron microscope (SEM). The corrosive elements and paths were analyzed and confirmed by EDS. The corrosion resistance of different component packaging was evaluated through one year of application comparison and verification at site. And the corrosion resistance of the coating was evaluated by constant salt mist and alternating salt mist comparison test from the perspective of PCBA coating. Results After failure analysis of the thick-film resistor and SMD LED, it was found that components were corroded by AgS generated from the sulfur element from the gaps close to the silver coating. Thick-film resistor and SMD LED with anti-vulcanization materials can effectively cut the invasion path of sulfur element in air to avoid corrosion failure. On the other hand, according to the 168 h of constant salt mist test and 144 h of alternating salt mist test, with the increase of the coating thickness and viscosity of varnish, the corrosion resistance of the PCBA increased and the metallic pins got better protection. Conclusion Choosing right packaging component and increasing coating thickness and viscosity of varnish can effectively improve the corrosion resistance of the PCBA. The research provides references for selection of anti-corrosion materials and optimization of coating parameters. |
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