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Humiseal 1A33 conformal coating using automated atomized spray

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Humiseal 1A33 conformal coating using automated atomized spray | 3 July, 2018

Reaching out to all conformal coating experts, please help!

While setting up conformal coating using the automated atomized spray, we observing issues associated with conformal coating wetting on the following regions:

1) Component edges 2) Metallic surfaces

We are conducting a wash with Kyzen Aquanox A4241 liquid to clean flux residues and using Oxygen only plasma to deal with surface energy issues. Visibly, we don't see flux residue under the microscope. Should we consider using other gases that would affect the contact angle of metal surfaces (Maybe, argon????) Are there any detrimental effect of oxygen-based plasma cleaning on metallic surfaces.

The material that we are utilizing for this purpose is Humiseal 1A33 Urethane based conformal coating compound mixed with the recommended thinner in a ratio of 1:4 (as supported by the material TDS). Should we consider increasing viscosity?

Are there any ways to improve metal wetting such as soldered areas, gull wings, traces and exposed BGA pads? (Hard limits: Can not use coupling compound interfaces such as organosilanes, cannot change coating material)

How can we avoid shadowing in areas of high density/complexity?

We have enough leeway to vary atomizing air pressure, tank pressure, spray pressure, dwell time, cure method, number of coats, a volume of material dispensed.

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Humiseal 1A33 conformal coating using automated atomized spray | 14 August, 2018

A couple of things to try as I just went through this myself.

Checkout this link for pointers on plasma cleaning...

I ended up going with a process that employs multiple, very thin, atomized passes to build up to a thickness of 0.02"-0.025". Specifically, running more thinner than coating (ratio of about 1.15:1), along with a higher than normal atomization pressure to help flash off most of the thinner as it's sprayed.

20 passes later (mix of straight down and angled) and I have a uniformly coated assembly that's almost tack free straight from the machine (Asymtek SL-940/EFD781 Dispense head).

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Humiseal 1A33 conformal coating using automated atomized spray | 18 August, 2018

Hey Phil,

i'm just curious what your rework processes are for your hardware after conformal coating is applied (if any). I'm interested in conformal coating as our hardware can be exposed to moisture rich environments at customer sites but to my knowledge this limits our ability to service the hardware for future repairs.

would be interested to hear details from someone who has implemented a conformal coating process.

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Humiseal 1A33 conformal coating using automated atomized spray | 20 August, 2018

Not entirely clear on your question. We don't coat any of our hardware (assemblies are coated prior to hardware installation), so if coating needs to be reworked after this, then hardware removal is needed.

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