Hello,

I must get some conformal coating to prepare some circuits that will be exposed to some salt-bearing water. (Not directly, but they will be around some water and could get tiny drops by accident.)

I noticed that Digi-Key does not seem to carry conformal coating - is this true? Newark has some but seem to have long lead times on them all. Mouser seems to have some.

Also I noticed three types. There is silicone, urethane, and acrylic. Which do you use and why?

I probably want the silicone because I guess it's better for moisture, but what are the reasons one would use the others?

And where do you buy yours?

Thanks!

 

You raise some interesting points. It has been awhile since I bought my can of spray acrylic from DigiKey. I went to the Mouser site and reviewed the TechSpray products. Surprisingly, the datasheet descriptions for relative repairability do not agree with the company's own selection chart. For example, the silicones are shown to have easier repair than the acrylic on the datasheet, but the selection chart shows it the other way around (i.e., silicones = 3; acrylic = 5; PU = 2). The selection chart (http://www.techspray.com/newinfo/2106.pdf) seems to make more sense to me, so here it is:

If resistance to moisture is your main consideration, it looks like the silicones are best, but they have slow cure times, are hard to repair, and are less resistant to arcing that the acrylics. My concern about silicone vs. the others is that they generally have poor peel strength. Thus, while the undamaged coating is extremely resistant to water, once the surface is damaged, water may be able to spread under the surface more easily or the coating may be easily peeled from the entire board. I have never used that spray, so that is just conjecture. I do think the silicone would be worth a test.

John