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Bubbles in Conformal Coating

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#57795

Bubbles in Conformal Coating | 16 January, 2009

I am using Humiseal 1B31 conformal coating and xylene mix on a PVA coating machine. Bubbles are appearing between the pins of LCCs mainly and bubbling is worse when put through the IR oven.

Does anyone have any suggestions or tips to elliminate this problem??

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#57796

Bubbles in Conformal Coating | 16 January, 2009

That the bubbling gets worse when you run the board through the oven indicates the issue is with the balance between releasing volatiles and cure.

Try one of these ideas: * Adjust the atomization pressure, nozzle size, temperature or viscosity of the coating (thin or thicken it). If any of these are out of the process window, you can get bubbles. Try a controlled experiment and you should find the exact window. * Adjust your cure cycle. If the surface is allowed to skin over prior to removing solvent from underneath, you will get bubbles.

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#57798

Bubbles in Conformal Coating | 16 January, 2009

Hi Steve,

Make sure your spray head is all the way down. If so, try slowing your rate of speed over the part. Which head are you using to coat this part?

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#57811

Bubbles in Conformal Coating | 19 January, 2009

Thank you for all of the advice.

I am using the extended spray for these cards.

Humiseal have recommended using their own thinners 600 instead, so will run some trials with this and also the humiseal pre-mixed material (at the moment we mix our own 70/30)

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#57853

Bubbles in Conformal Coating | 22 January, 2009

Humiseal recommends a 1 to 1 mix ratio of 1B31 and Thinner 521. I have for that I need to thin my ratio more to get humiseal to spray correctly in our PVA650. Also I am using Humiseal 1B73 but the tech data sheets say the same for spraying. Try thinning it more, I think you will have much better results.

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#57961

Bubbles in Conformal Coating | 3 February, 2009

We use PVA and I have had bubbles that came from the pressure in the pressure pot being to high. Also the material filter was slightly clogged. I'm not sure of your setup hope this helps.

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#57969

Bubbles in Conformal Coating | 3 February, 2009

I would also suggest looking at your ramp rate in the cure oven. We noticed that accelerated heating increased the "gas out" of the solvent. We run 1A33 and and do not exceed a .5/degC ramp rate.

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