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

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SMT electronics assembly manufacturing forum.

Problem with conformal coating


Problem with conformal coating | 17 February, 2005

I use conformal coating DYMAX #984-LVUF and I don't know if it's a problem of viscosity but 0805 components are not covered properly. We use a dispensor to applied it and we cured it by UV. Even if I apply a thicker layer, the coating seems to have problem to stick correctly to the top corners of the components. So if we apply water on top of the component, we can see that the coating do not cover the component correctly.

Is someone ever had this problem and what do you suggest to do?


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Problem with conformal coating | 17 February, 2005

We're not familiar with your DYMAX #984-LVUF. The problem is not with your conformal coating. The problem is with your 0805 [and not all of 0805, probably just those from a specific supplier].

This lack of coverage of components is called dewetting. Dewetting is caused by mold release residues on the component bodies. Component fabricators apply a material to the molds used to form components that makes it easier to get the component out of the mold. * Is this dewetting a problem? Not really. Although it would be better to obtain components that do not exhibit this problem. * Dewetting could become a problem, if you clean the assembly and the mold release is silicone. When cleaning, you could spread the silicone over the surface of the assembly. [And probably all succeeding assemblies that you run through the cleaner. Bummer.]

We suggest that you inspect your coated boards under UV [black] light. If the dewetting is limited to component bodies, push on. Otherwise you may want involve a cleaning specialist.

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Problem with conformal coating | 18 February, 2005

Thanks Dave,

The problem is on all 0805. Do you think it could be a reaction with the flux from the wave or the one in the paste. Do you think the problem is the viscosity of the coating. SPEC = Viscosity 150cP nominal ASTM D-1384.

I ask you all these questions because the representative want to do other tests instead of getting a clear answer. He don't know what to do and we don't have the time to test and test and test ...

What kind of coating are you using on your PCB ? Do you have the same problem as mine ?

Thanks Frank R.

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Problem with conformal coating | 18 February, 2005

It's weird that it would be just 0805. When we see this it relates to a single part number and it goes way after a time. We use a Humiseal 1B73.

I've emailed you the contact for a person that is very knowledgeable on conformal coatings.

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Problem with conformal coating | 18 February, 2005

Frank R, I believe the Dymax #984-LVUF is a POLYURETHANE RESIN. I have used Humiseal 1A27 and 1A33 for several years with great success. Both of these materials are High VOC materials.

If your customer does not require these materials to be aproved by UL or IPC-CC-830 than go with Aqueous UR 1122 or 1H80. Both of these materials are Low VOC or VOC Free.

Best of Luck Jan C-C Technologies Inc.

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Problem with conformal coating | 23 February, 2005


Few questions concerning your Umiseal 1B73.

To cure your Acrylic coating do you respect specification ( 2Hrs-170degree F) or you go faster than that?

What do you use to cure it?

Do you have to clean your nozzles each day or each monday because of drying coating?

Is there a procedure to evaluate Coatings?

Thanks Frank

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Problem with conformal coating | 23 February, 2005

We: * Cure 1B73 according to spec in a heat box, like a Blue-M * Clean nozzles [one set in use, one set being cleaned] in thinner in a bronson ultrasonic cleaner * Haven't evaluated coatings in years, but would do it according to J-STD-001C, Reqmnts Soldered Electrical & Electronics Assemblies, Appendix B

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Problem with conformal coating | 21 March, 2005

Some UV cure coatings do not have the correct rheology for sticking to small sharp corners. 984 is one of them. MicroCoat Technologies, Allen, TX makes one that works every time.

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Problem with conformal coating | 10 April, 2005

Normally, some conformal coatings do not have very good wetting properties, that should be basic function of a good coating material (the same reqirement as avoid bubbles during coating process)!

For UV curing conformal coatings, you can try Lackwerke Peters Twin Cure DSL 1600! Other conventional conformal coatings, Peters SL1307 or SL1301ECO-FLZ are very good, since they have very high solid content, which means very low VOC! If you want more environmental friendly coating, please try SL1305AQ which water based material, no bad smell emitting out!!

If you specially wanted very good wetting function, and your assembled PCB is not very clean, try to use SL1309N which is more suitable! or

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Problem with conformal coating | 23 November, 2006

The solid content of 1B73 is too low, especiall when you add large amount of thinner, not easy to get enough coating thickness.

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