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Determining conformal coating protection

Christopher Hunt (National Physical Laboratory, Teddington, UK)
Angela Mensah (National Physical Laboratory, Teddington, UK)
Anthony Buxton (PRA Coatings Technology Centre, Hampton, UK)
Richard Holman (PRA Coatings Technology Centre, Hampton, UK)

Soldering & Surface Mount Technology

ISSN: 0954-0911

Article publication date: 1 October 2006

770

Abstract

Purpose

This work sets out to characterise the protective properties of conformal coatings and how they degrade.

Design/methodology/approach

The approach dosed several commercial coatings with two different contaminants, a synthetic generic flux mixture of dibasic acids in both a solvent‐ and water‐based carrier, and sodium chloride. The protective properties were monitored using three complementary techniques: surface insulation resistance measurements, sequential electrochemical reduction analysis, and diffusion measurements.

Findings

The experimental approach was verified and the SIR measurements were shown to be the most valuable. Coatings offered varying levels of resistance to the contaminants, with the silicone coating being the most resistant. The flux variants generally proved more harmful to the coatings, suggesting that flux diffusion through the coating exceeded that of NaCl and hence led to greater electrochemical corrosion. Flux transmission through the coatings was verified by the diffusion measurements.

Research limitations/implications

The project only investigated a limited number of contaminates on simple single sided boards. Future work will investigate coverage effects and a wider range of contaminants.

Practical implications

The work shows that coatings can allow diffusion of contaminates, particularly organics, which can lead to corrosion. The test methodology described here can be used to characterise coating susceptibility.

Originality/value

This work starts to develop for the first time a test methodology to characterise the protective properties of conformal coatings, and shows that flux, and hence other similar organic contaminants, may represent a protection challenge for some coating chemistries.

Keywords

Citation

Hunt, C., Mensah, A., Buxton, A. and Holman, R. (2006), "Determining conformal coating protection", Soldering & Surface Mount Technology, Vol. 18 No. 4, pp. 38-47. https://doi.org/10.1108/09540910610717893

Publisher

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Emerald Group Publishing Limited

Copyright © 2006, Emerald Group Publishing Limited

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