Conformal coating spray

[kcs]

I want to do conformal coating for some of my PCBs. I have purchased acrylic spray can from a well-known   manufacturer and did some experiments. I have generously sprayed and let it dry, then I have repeated this procedure 5 times. However, the coating was far from perfect. All the sharp edges were not coated. For example, pin and IC package edges. I have marked those places in the first photo. In the second photo you can clearly see that sharp corner is no properly coated even when thickness of conformal coating is relatively high (I guess to achieve that thickness I would need to spray at least 50 times or use dip/brush coating). The third image illustrates what I was expecting to get (on the left) and what came out (on the right).

Can anyone share his/her experience on doing conformal coating at home?
Is there any special techniques how to use spray conformal coating and achieve even coating everywhere (including edges of components)?

[rdl]

You won't get the results you want from anything in a spray can. That kind of application requires very low viscosity, so the material is going to have an unavoidable tendency to pull away from sharp edges. What you need for that effect is a thick, fast curing material, such as UV cured, applied by curtain coat or something similar.

You might try hanging the board upside down during and/or after coating it, but it may not help that much.

[kcs]

You won't get the results you want from anything in a spray can.

I see. I wish I knew that before... Can I use that spray can for any other application or is it generally speaking unusable rubbish?

Do you know any UV curable conformal coating that is sold in small quantities and is not restricted to professional usage (cannot be sold to regular customers)?

[SeanB]

Spray a little of the spray into a small solvent proof disposable bowl, and leave it to boil off solvent for a few minutes, till it becomes a thick liquid. Then use a small brush, or some paper towel rolled up into a thin tube, to paint the coat onto the board where needed. The thickened up coating will dry and shrink, but will leave a thicker film. You will likely be dipping the thickened sealer using a few dabs with it rather than painting. It works quite well and allows you to spray the whole board evenly and only add extra to the edges and such where you want a thicker film coat.

[calexanian]

We use a product called Humiseal. Its thick like honey. It remains a little soft like silastic but has the electrical and mechanical properties for use in SMT potting. We dribble it on critical areas on some of our products. It does not remove easily when cured though.

[kcs]

SeanB, have you tried that technique? Do you have any photos to share with the final result?
It looks to be quite hard technique, if coating mess all over the PCB is not desirable. But I could be wrong here, just my first impressions.

We use a product called Humiseal.

Humiseal is a brand, what is the exact product number? http://www.humiseal.com/product-selector/
Also, it looks like it will be quite hard to get it in small quantities.

[calexanian]

We use Humiseal type 1C49 and it is available in quart cans. It has a 6 month shelf life but if you keep it sealed in the fridge you can stretch that out to a couple years. As an alternative similar product we have used Loctite 5140 potting compound. That comes available in a caulking gun caulking gun tube.  an opec tube of that will last over a year in the fridge as well. Just make sure you plug it. Both of these products use both heat and moisture to cure. At room temperature they cure overnight. Both have a consistency of honey and flow out a little but build up thick. On larger I.C.'s i put a dollop on the top and smear it around to ensure all of the pins are covered. I have never had need to use a vacuum to pull the bubbles out. Occasionally one will occur but due to the nature of our products that tends not to be a problem. Your mileage will vary as they say.