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Parylene coating - spots defect around via holes & other flat surface

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#76421

Parylene coating - spots defect around via holes & other flat surface | 5 October, 2016

My fact is EMS/PCBA-concerned parylene coating that found coating spots around via holes and other flat surface but not 100% found in batch just a few boards per round.

The flow : SMT --> Rinse IPA 5 Min --> Treathment/soak IPA50%+SILENT50% 5Min --> Baking 60C/30Min --> Parylene coating (around 8Hr in chamber) --> Found defect spot.

We have simulated and ensure board drying before parylene that still have spots. Need help - Thank you

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#76427

Parylene coating - spots defect around via holes & other flat surface | 6 October, 2016

Looks like moisture bubbling out of the board. I doubt that your baking at 60*C for a half hour is going to do very much to dewet the board. 60*C is warm to the touch, that's it!!! Water boils at 100*C. 60*C is the temperature of a cup of Dunkin.

Crank it UP!!!

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#76428

Parylene coating - spots defect around via holes & other flat surface | 6 October, 2016

am worrying on a hight temp that will affect to others components mounted on board or not such ICs..

Thank you davef -

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#76429

Parylene coating - spots defect around via holes & other flat surface | 7 October, 2016

Two things ...

A friend in the contract coating business said: "... the board is not being baked out long enough, 30 min is certainly not long enough depending on how many layers this board is, as the vacuum (from the parylene process) is pulling the remaining moisture out from inside the board layers and via."

With regard to a board baking recipe: Refer to IPC-1601 - Printed Board Handling and Storage Guidelines [http://www.ipc.org/TOC/IPC-1601A.pdf]. IPC-1601 completely covers circuit board bake-out, methods for determining optimum bake time and temperature, caveats for certain board plating finishes, and on and on. I'd start with 48 hours at 100*C, after confirming that that won't damage components on the board. But then again you should use IPC-1601 to keep yourself out of trouble.

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Plasma Prior to Conformal Coating

Heller Industries Mark 5获得了 2015年中国SMT远见奖 - 回焊炉领域