To add a professional finish to my boards and protect them a bit I like to cover them with a solder mask. To do this I have used a 3 mils Dry Film Solder Mask (DFSM) Dynamask 5030 from the Dynamask 3000 series. Applying this at home requires the following.

• KiCad
• Inkscape

• Dynamask 5030 3mils dry film solder mask
• Laminator
• Stick tape
• some paper, a little larger than your PCB.
• knife (I use a scalpel)
• brush
• developing tray
• laser transparency sheets
• laser printer
• super glue
• glass sheet
• 2 x tins of beans (or similar)
• 100ml Deionized water
• 1g of sodium carbonate (soda ash)
• Mixing flask
• 395nm UV light 100W
• UV protective glasses
• Yellow light (I use an LED desk lamp with some yellow film wrapped round it).
• Oven
• Baking paper

• 1 In the KiCad PCB editor plot the back mask to an SVG file. If you are doing a duel sided board then also plot the from mask but as a mirrored image.
• 2 In Inkscape I then assemble the images into the same file being sure to leave plenty of whitespace around them. Now print two copies of the image onto a transparency, I set my printer to transparency as the media.
• 3 Next I use super glue to stick the two images on top of one another being careful to ensure they are aligned and the glue does not get near the image (hence all of the whitespace).
• 4 Now set up a 'darkroom and ensure you are working under yellow light. Here you can unwrap the DFSM without exposing it.
• 5 Now cut out a section of the DFSM just slightly larger than your PCB. It really helps if your PCB is larger than the etched section then you have some edges to play with. Return the DFSM to its light proof storage.
• 6 The DFSM has two sides a matte side and a shiny side, both are covered with a protective film. First we need to remove the matte film as it is covering the sticky side. Use two pits of tape, one on each side, to separate the film, but do not peel the whole thing off yet!
• 7 Stick the DFSM to your PCB on the 'top' edge of the PCB. By top I mean the end you will feed into the laminator.
• 8 In this step you really need an extra pare of hands but it can be done! Fold the paper over the BCP with the fold at the top end and feed it into a heated laminator keeping a tight grip on the matte film. The idea here is: as the PCB is pulled into the laminator you keep a tight grip on the protective film to stop it going through with the PCB. This has the effect of keeping the DFSM flat and wrinkle free as it goes through the laminator and ensures a good clean adhesion. The paper should be slightly wider than the PCB and the DFSM and is used to prevent the sticky DFSM material from sticking to the heated rollers. Check you have a good clean adhesion without wrinkles*.
• 9 If you are doing both sides of the PCB repeats steps 5 to 8 for the reverse side.
• 10 Now put the transparency with the appropriate mask over the PCB being sure to align the mask Markes with the locations you need to mask off (typically the pads, etc). Once this is aligned carefully place the glass sheet over the PCB and transparency and hold it down with the two tins, be careful that the tins are not covering the PCB. Then balance the UV lamp on the tins directly above the PCB.
• 11 Put on the UV protective glasses and turn on the lamp for 30 seconds.
• 12 If you are doing a two sided board repeat steps 10 and 11 for the other side.
• 13 Now don your protective gloves and glasses and mix the water and sodium carbonate in a flask. Once the sodium carbonate has dissolved pour the developer into the developing tray.
• 14 Using some sticky tape remove the protective film from the DFSM and put it into the developer. You can use a brush to help remove the unexposed DFSM leaving the copper clear. If you are doing a two sided board turn the board after a few seconds and ensure both sides are clear where they need to be. You can now work under regular lighting conditions.
• 15 Rinse the PCB under running water and part dry.
• 16 Now to fix the DFSM, put on the protective UV glasses and give each side coated with DFSM another 2 minutes under UV.
• 17 In a preheated oven (heated to 150C) place piece of baking paper on a rack, put the PCB on that, and bake it for an hour (if it's two sided turn it half way through).
• 18 Let the PCB cool and it is ready for drilling if it is a through hole project.

• Should you get a bad adhesion in step 8, bathe the board in developer to remove the DFSM, rinse and clean the PCB, then retry steps 5 to 8.