Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

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Un-cured conformal coating



Un-cured conformal coating | 27 October, 2004

We are producing boards with Alpha 591S RMA No-Clean paste and are coating after SMC with Dow silicone ( toluene solvent based) conformal coating. We have experienced several failures due to soft shorts ( electrochemical migration?) We have also observed areas of uncured material under several ICs.

Wondering if anyone has experienced similar issues with these materials?


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Un-cured conformal coating | 29 October, 2004

Electrochemical migration under conformal coating: That's possible. Very few conformal coatings are water resistant. So, if you have ionic material on your board, standback.

Uncured material under several IC: Materials like yours need moisture from the atmosphere to cure. So, when the material at the edges of the IC cure, the material under the IC virtually stops curing. It can take weeks for it to cure.

Recognize that toluene is a mild health hazard.

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Un-cured conformal coating | 29 October, 2004

Davef, thanks for inputs. I think your correct, we have since obtained some ionic analysis and sure enough there is relatively high chlorides on the bare pcbs.

The toluene is controlled within dip tank / drying system, almost no exposure to workers.

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