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Conformal coating (again)


Loz

#26986

Conformal coating (again) | 26 January, 2004

I have a product that has earthing/positioning holes, as they are to be used for earthing purposes they need to be free from conformal coating. This pcb is double sided. I have used spot/peelable mask to protect these holes. However when the conformal coating has been applied (using a spray can) the coating on the 1st side appears to be de-wetting around the masked areas. The 2nd side is not showing any signs of this at all. I assumed that the peelable mask had introduced contamination. If this is not the case can anyone offer an explanation as to why one side bad, other good?

Thanks. Loz

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Pete B

#26992

Conformal coating (again) | 26 January, 2004

Some questions:

Is the peelable/spot masking only being applied to the earthing points on the one side or to both sides?

Is the peelable mask you are using specifically designed for coating masking or is it the same as that you use for masking solderable surfaces prior to wave soldering?

What type of conformal coating material are you using?

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#26996

Conformal coating (again) | 26 January, 2004

Some temporary solder masks outgas ammonia as they cure. It's possible that the first side cured and out gassed through the grounding hole. But when the second side cured, it outgassed between the board and the coating and in so doing reacted with something on the surface of the board.

It's also possible that the second side was not properly cured when you applied the mask.

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Loz

#27001

Conformal coating (again) | 27 January, 2004

Thanks Dave, sounds totally plausible. In answer to Pete B's questions

1. Spot mask IS only being applied to earthing points, top and bottom side. 2. Unsure. Speaking to manufacturer they are telling me it is compatable. However data sheet is vague. (does contain ammonia though) 3.Conformal coating is acrylic.

It may just have been a one off as a second pcb has not displayed the same kinds of problems.

Thanks,

Loz.

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Rob O

#27002

Conformal coating (again) | 27 January, 2004

Try using Kapton Tape or masking tape dots instead of the liquid mask.

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#27008

Conformal coating (again) | 27 January, 2004

I would suggest trying an acrylic peelable mask. In most cases peelable temporary masks are latex materials. Since you use an acrylic conformal coating it makes sense to use a mask with the same make up to avoid incompatabilities. Link to acrylic mask http://www.interfluxusa.com/misc.html

hope this helps, Patrick

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Maryann

#27199

Conformal coating (again) | 11 February, 2004

Our company strictly does selective conformal coating applications for the customer. We will quite often see one side looks great, and the other side doesn't. We often see dewetting around holes, and have found this can be a possible flux build up. Although if you look at it, you may not visibly see contamination. A simple water or IPA wash has solved this for us. Although I am not familiar with masking materials, as we simply program the equipment to spray around what isn't coated.

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