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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Help with dewetting

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Help with dewetting | 24 May, 2010

I am new Engineer in conformal coating and I am looking for help with dewetting. What "Tricks of the trade" can I try to reduce or eliminate dewetting? We use a lot of Conap CE 1155 and Humiseal 1B73? Any help would be appreciated!!!

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Help with dewetting | 25 May, 2010

Where on the assembly is the dewetting occurring?

Factors that influence dewetting usually involve non-ionic contamination such as: * Residues from board manufacture including silicone surfactants from solder resist & HASL rinse contamination * Component residues like mold release agents * Silicone oil from adhesives in production. * Soldering process residues * Cleaning bath contamination where rinsing has failed * Operator handling that adds contaminants

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Help with dewetting | 25 May, 2010

I don't have experience with 1B73. I do have a ton of experience with CE-1155. There are a couple of gotchas with this material. First and foremost is that it HATES silicone residue. If the material is not sticking to parts and they aren't ceramic, test them for silicone. The other trick with this is to rinse the board with IPA for 5 minutes prior to coating. Once the product is clean, always handle with gloves. Bake the assemblies out prior to coating to drive off any moisture. I personally like to give the assemblies 100-125C for 6 hours. Boards should be allowed to cool and should be coated immediately afterward. Regards, Justin

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Help with dewetting | 25 May, 2010

Hello, I have no experience with CE-1155 but a ton with 1B73. I would say Justin hit it right on the head. 1B73 does not like to be anywhere near silicone residues. We make sure the boards are handled with gloves after wash, before coat. Unfortunately we dam off the bottom of a couple of connectors that the coating likes to wick up and inside using Dow 3140 silicone. If the operators are not absolutely meticulous applying that and get a spot, finger print, wisp (long strand) of RTV where it shouldnt be, the coating runs and hides!

We also see it on the body of some ICs but i think that is less of a big deal...

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