SMTA International Conference Proceedings

Improved Condensation Testing to Evaluate Protection Performance of Conformal Coatings Under Different Condensation Levels

Authors: Martin Wickham and Ling Zou
Company: National Physical Laboratory
Date Published: 10/14/2018   Conference: SMTA International

Seika Machinery, Inc.

Abstract: Achieving high reliability in service is very important for the electronics circuits. Failure by electrochemical migration is an increasing issue as electronic feature sizes diminish, and service voltages and environmental stresses increase. The presence of contaminants under applied bias and with moisture, facilitate electrochemical corrosion processes that result in circuit failures. Electrochemical failure is very sensitive to moisture. When moving from ~100 nm liquid films in damp environments (85oC/85%RH) to visible liquid water layers in condensation, metallic corrosion on circuit assemblies can be significantly accelerated. Failures can occur in a few minutes.

Conformal coatings have been widely used to protect electric circuits from harsh service environments, particularly under high humidity and condensation conditions. In this work, special designed assemblies have been coated by industry partners using different conformal coatings and processes. The test vehicles were assembled with a range of components and different solder pastes. A newly developed condensation approach with Surface Insulation Resistance (SIR) measurement was used to evaluate protection performance of the different coatings on the assemblies. A short term test methodology using three increasing levels of condensation over a 24 hour period, has been demonstrated to be successful in discriminating the condensation protection performances of different coatings. Coating protection strongly depends on component types and coating coverage. Coatings provide different levels of protection for different component types due to the coverage.

Key Words: 

Surface Insulation Resistance, Condensation, Coatings

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