I worked for a telecom company that had sites in the deserts, jungles, mountains and regular built up area's. All boards were built using Aim 291/293 No clean solder paste. (all boards built to Bellcore standard)
The boards were coated with Dymax urethane confroaml coat for obvious reasons.No adhesion problems. In the five years at the telecom company i did not see any boards returned for confromal coat adhesion problems. There were units operating in the field for 10 or more years that were built with no-clean solder paste, coated with urethane coating.
No-clean flux off the wave solder is another problem. If the flux sprayer was turned up to high on the wave solder. the bottom of the board was saturated in no clean flux.Vague white marks could be seen on the edge of the boards where the no-clean flux collected and dripped off.(i turned down the flux sprayer level without taking away from solder quality).If the majority of this built up of no-clean flux residue were not removed (a gentle wipe with a cotton swab soaked in alcohol), bubbles would form in the conformal coating after heat curing the urethane conformal coat. The conformal coat adhered nicely to the area's without the excess no-clean flux residue.
Verification for thickness and adhesion was performed on the conformal coat as per IPC-650 test methods.
If more info is required, post your E-mail address or phone number and i will get back to ya.Hope this helps.
Jim M.
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