The purpose of this paper is to present a new test method (tape peel method) to evaluate conformal coating adhesion to electronic assemblies.
The key issue for this method is the low cohesive force of conformal coatings, and hence selection of a supporting material to peel the coating from the substrate is critical. A suitable cloth material (35 per cent cotton +75 per cent polyester with 20 per cent open area) has been selected as a peel tape, and achieved the best bonding with coatings, and the smallest affect on the coating curing process. Using the tape, the peel force of the coating from the electronic assembly, can be measured quantitatively, and hence the adhesion performance of the conformal coating assessed.
The method was validated using different coating types, substrate materials (bare laminate with and without resist, copper clad laminate, and contaminated laminate material), assemblies and components. The results demonstrated that the tape peel test is a sensitive method for measuring coating adhesion on different materials found on PCB assemblies. Coating adhesion was found not to be effected by a wide range flux residues, but components and some resists presented a far greater coating challenge, with some coatings achieving very low adhesion values.
This new method for evaluating conformal coating adhesion to electronic assemblies will be of benefit to coating developers and users, and help to minimise adhesion failures in service. The test has been demonstrated to be sensitive to a number of process and material variables.
Zou, L. and Hunt, C. (2012), "A new conformal coating adhesion test for electronic assemblies", Soldering & Surface Mount Technology, Vol. 24 No. 1, pp. 12-21. https://doi.org/10.1108/09540911211198513Download as .RIS
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