UV curable solder mask

Short tutorial about using UV curable solder mask.
It is an update to my original PCB making tutorial: https://www.youtube.com/watch?v=p2kFazl-aEE
See explanation below:

In this video I used standard transparency film printed with laser printer. Usually I use optical film because of greater contrast, but here I wanted to present a method doable by everybody.

The solder mask paint I used can be bought from ebay:

https://www.ebay.com/itm/PCB-UV-Curable-Solder-Mask-Repairing-Paint-Green-100g-/200622507317?pt=LH_DefaultDomain_0&hash=item2eb6088535

It is pretty cheap, and enough for a lifetime for a hobbyist. It has very good scratch resistance, resistant to chemicals, heat resistance even to 320*C soldering iron, and gives good surface finish used with cellophane.

The key for a good, well cured coating is to obtain an even and thin film on the PCB.
The steps are the followings:
- Prepare the PCB – it should be cleaned thoroughly after etching.
- Prepare the film: It is crucial to have a good contrast otherwise either you need to lower the exposure and it will cure partially and will not adhere well to the board, or with a longer exposure it can cure on the pads also and you can not wash it down.
For a good contrast with laser transparency – print one normal and one mirrored image, then put them together with the toner part facing each other to prevent shadow ghosting.
- Stir well the paint (it is very viscous) and put a droplet in the middle of the PCB board. You can stretch it a bit but do not extend it on the board (it should be done using the cellophane to prevent air bubles)
- Put the cellophane over the board with the paint droplet in the middle, and stretch the paint using a credit card or similar. Don’t press it too hard otherwise the cellophane will stretch and will form wrinkles.
- Stretch the paint evenly on the surface of the board trying to achieve the thinnest coating possible.
- Put the film over the cellophane, align it to the PCB’s artwork, cover with a sheet of glass and press it some more to make the whole ting more even.
- Expose under UV light ( I used 12W on 20cm for 10min 30sec. )
- Peel down carefully the cellophane and wipe down the uncured paint from the pads.
- Expose for further 10min under UV light to harden the paint further (you can use the sun light also for this)
- Proceed with the other side for double side boards.
- Enjoy the result.

With a good film I obtained 50 micron details also (square pins for a 0201 component)

Details about the exposure device:

https://nagyizeeuv.blogspot.ro/

Good luck