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Professional Home Brew PCB: Creating a solder mask using UV curable paint

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Step 3: Applying the mask

Now set the board aside somewhere dark to dry for a several hours. I put mine in a sealed cardboard box to make sure it was not exposed.

You will now need to print the solder mask that will cover the board and protect the pads you wish to solder from being hardened in the sun. If you are using Fritzing to design your PCB then when you export it it will create a solder mask PDF you can print as well.

If you use a laser printer to print your mask then make sure you use the highest quality possible so it has the most toner on it to create an effective block for the UV light from the sun.

Cut your mask down to size so it is the same size as your PCB.

Once your PCB is dry it's time position your mask over your board and then use a sheet of glass to push the mask down flush on the board. This will avoid the chance of shadows on the board protected things you did not intend.

Place it all in direct sunlight for about 30 minutes.

Now the UV light should have hardened all but the areas protected by the mask, take it inside and remove the mask and lightly scrub the pads with turps using a toothbrush.

The non exposed areas should wash away. Rinse the board in water to remove any excess turps. It should now be ready to solder.
 
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sleemanj1 year ago
I'd like to add here that readers should look at the comments on page 1 before attempting to "dry" the board.  I didn't, and wondered why I had a lot of trouble. 

Drying the board is not necessary at all, infact, it's almost impossible, and if you cook the board to dry it then you're making it very hard on yourself.  Perhaps sdelaney had a different mixture, or spread it really really really really thin, but I couldn't get good results with his instructions to dry the ink first.

The ebay sellers are actually on the money, if it sounds a little odd, put a dollop of ink on the board, put a transparent, THIN, plastic film over the top and spread it around so that it's nicely covered.  The plastic film you use needs to be as clear and thin as possible.  You don't need to be in a dark room, it's not that sensitive, but don't go doing it in direct sunlight.  You can also use a toothpick to "paint" the board first, then put on your transparent film, this might help you get a more even coverage.

Leave the film in place and align your artwork on top of the film, toner side DOWN, so you have a sandwich like this: board, then ink, then transparent film, then tonor, then whatever you printed the tonor on. 

Now put a piece of glass on top to press it together, and expose to the sunlight, or make yourself a UV exposure box, my UV box (made from an old gutted scanner bed from a multifunction printer, UV leds and a couple hours of soldering) sufficiently hardens the ink in 55 seconds or so, experiment with scrap pieces of PCB to get the timing right, you want the exposed areas hard enough to withstand wiping or light scrubbing, but the covered areas to be soft enough that they are removed.

Once hardened enough, just peel off the plastic film (it doesn't really stick to plastic), and wash the board in turps (or acetone, or ....) gently at first in case it's still a little soft, the pads will wipe clean.  Once you've got the pads cleaned, expose it for a few more minutes to fully cure the ink. 

This ink is VERY tough once exposed, VERY tough, it does not dissolve, but you can scrape it off pads with the tip of a craft knife if you need to touch it up.
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