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I have made my own PCB for a project which carry AC supply, and I want to know all about it: If due to moisture it may short out or not, and how to protect it from moisture.

I have seen UV curable solder mask, but I didn't find it in any store, and I have got to some shops, they have something spray or transparent liquid which provides protection against moisture but it was costly. I can't buy it for just 3-4 PCBs.

Please suggest me any other cheap way to provide a protective layer. For a moment I thought to apply oil paint or hot glue on it, but I didn't know if it will work.

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  • \$\begingroup\$ What is your definition of moisture? How big is the board? What is it housed in? Does anything get hot on the board? \$\endgroup\$ – Trevor_G Mar 22 '17 at 3:27
  • \$\begingroup\$ You may be looking for a Thermal Encapsulant. \$\endgroup\$ – Misunderstood Mar 22 '17 at 3:34
  • \$\begingroup\$ It's 5cm×10cm size their are 4 similar circuits consisting triac bt136 use to switch on off Ac supply I have tested it daily for a month month but I find nothing hot is their any need of protective layer to prevent it from short circuit or rusting of track \$\endgroup\$ – Mayur Mar 22 '17 at 3:35
  • \$\begingroup\$ Is it exposed to the elements. Or will it be installed in a condensing environment... like a bathroom... \$\endgroup\$ – Trevor_G Mar 22 '17 at 3:39
  • \$\begingroup\$ I think you may be looking for a conformal coat, or epoxy potting compound. It is expensive when you buy in small quantities. \$\endgroup\$ – mkeith Mar 22 '17 at 4:11
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It really depends on the application.

If it is intended for indoor only in non condensing environments then you do not need a coating. Nothing will rust unless you are using steel screws or other fastenings.

If it is for a high humidity environment where condensation is likely then a conformal coating may be sufficient. There are a wide variety of options.

If it is intended for outdoor use where rain or other sources of water may enter the enclosure then "potting" the board in a resin or other material is usually required.

If all cases, especially where components are expected to get hot, special care must be taken to ensure that the heat transfer can still be maintained.

A wide variety of proper materials are available specifically for this purpose on the market that have the appropriate ratings and approvals. Many are specifically designed to have good heat transfer characteristics. I have to recommend you use one of these for your safety and the safety of anyone that might be using your boards.

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  • \$\begingroup\$ Having said all that. I have seen people dip their hobby boards in plain old varathane and hang them up to dry... Not sure it passes the flame test though. \$\endgroup\$ – Trevor_G Mar 22 '17 at 4:41
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If you are looking for extra cheap (like $1) protection you will not find it. I am using dry film solder mask (foil) which is simpler than wet UV curable solder mask you mentioned. I'm using Dynamask 5000.
For dry solder mask you need UV light and a cheap laminator.
The final PCB looks like a bought one.

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  • \$\begingroup\$ How much dry solder mask cost \$\endgroup\$ – Mayur Mar 22 '17 at 11:45
  • \$\begingroup\$ I buy slides of size A4, each for 3€. Or size 1m x 0.3m for 14€. That is foil. You can cut it to size of your PCB. \$\endgroup\$ – Chupacabras Mar 22 '17 at 12:07

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