PCBA (Printed Circuit Board Assembly) Conformal Coating Material and Thickness?

gohyl

Starting to get Involved
Conformal coating spray onto PCB results in this kind of condition. Anyone out there know what went wrong? This picture is taken under UV Light.

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outdoorsNW

Quite Involved in Discussions
New versions of IPC-A-610 H and J-STD-001 H released to day. I have not had chance to look at the new versions. J-STD-001 G has conformal coat acceptance requirements and I am assuming the new rev will also. The 830 series documents listed by others are process and design guides, not acceptance requirements.
 

blackholequasar

The Cheerful Diabetic
Conformal coating spray onto PCB results in this kind of condition. Anyone out there know what went wrong? This picture is taken under UV Light.

This could have been a couple of issues - one is board cleanliness. If they don't have a clean surface, the coating may not adhere. It also depends on the TYPE of coating your applying and the level of thinner that is being applied to the spray. It looks like the spray didn't cover everything evenly, there are definite missed areas. If this is acrylic based conformal coating, you can re-apply to these areas and bake/air dry. But if the board isn't cleaned prior to coating then you get really poor adhesion.

We recently had a huge cluster with 1A33 coating on our PCBs for a customer that had bubbles, orange peel and blushing along with pretty bad corner delamination. It turns out that they never cleaned the boards prior to coating them (which caused the delamination) and that they baked them incorrectly (which caused exgassing and bubbling)
 

gohyl

Starting to get Involved
Thank you very much guys. In terms of cleaning, what solvent is recommended? Moisture Curing Polyurethane. Coating material humiseal 1A20 and 521. Is such dewetting a reject? How is the rework be?
 

outdoorsNW

Quite Involved in Discussions
To figure out how to clean, you need to know what the contaminant is. What might the contaminant be? What is the current pre coating cleaning?
 
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