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Conformal coating mask dots and halos

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#61230

Conformal coating mask dots and halos | 25 February, 2010

We are using Humiseal 1B31 and polyester dots for masking. We are spraying this in a Binks sprayer mixed at almost 1:1 with 521 thinner. Whe are seeing the coating creating thin halos around the poly dots as if the dots are "rejecting" the coating. This leaves thin layer rings around the dots and is noticeable not only under UV light but in normal light. The thickness is below IPC spec in these areas. Respraying does not aleviate this either. Humiseal has no answer for this but is aware. Is anyone else seeing this? In military applications, this is not acceptable, yet polyimide and polyester dots are the only masking dots suggested. Any ideas?

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#61231

Conformal coating mask dots and halos | 25 February, 2010

My guess would be that the adhesive used on the dots contains silicone. We use 1B73 which is also acrylic and it hates silicone. We use silicone RTV to permanently mask around some connectors and unless its fully cured before coating it will cause lights areas around it like you describe.

Josh

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#61232

Conformal coating mask dots and halos | 25 February, 2010

It sounds like your poly dots are secreting something that affects coating thickness. Is this a function of the adhesive used by poly dot supplier?

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kpm

#61247

Conformal coating mask dots and halos | 26 February, 2010

If I had to guess I'd say they're using a silicone based adhesive.

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MGL

#61249

Conformal coating mask dots and halos | 26 February, 2010

Your masking dots are a silicone adhesive. Contact the supplier and tell them you need an acrylic adhesive on the same dots. Normally same cost and lead time.

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#61250

Conformal coating mask dots and halos | 26 February, 2010

Hey its probably the silicone adhesive

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kpm

#61254

Conformal coating mask dots and halos | 26 February, 2010

sorry jdumont I didn't see your post until after I posted mine for some reason. If I had seen it first I wouldn't have posted because yours covered it.

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#61268

Conformal coating mask dots and halos | 1 March, 2010

No problem just busting, trying to keep the mood light!

Cheers

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Lou

#61269

Conformal coating mask dots and halos | 1 March, 2010

Hey....I think it might be the silicone adhesive! LOL Yeah, that'll do it. We use simple Shercon paper dots. Work like a charm. No evidence of "de-wetting".

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