Quote:
Originally Posted by Bobsound
thankyou for your insights. The last PCBs I made were a number of years ago using the black sticky tape and an RS UV exposure box.
Do you use the sticky tape or a resist pen or some other technique?
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I create the artwork in MS 'PAINT' then to make the UV mask, I use an ink-jet printer to print the artwork onto 'micro-porous film' used for screen printing, which is far superior to normal OHP film. I don't use pre-sensitised UV laminate, I haven't done for some years as their exposure time seems rather sensitive and I always ended up with useless offcuts. For some years I used positive UV lacquer, self-sprayed from aerosols. If the board doesn't come out right, I'd then wipe off the UV resist with meths (AKA 'de-natured alcohol outside the UK) and re-spray the lacquer and have another go. However, this last year or so I've been using negative UV 'dry film' which is very cheap on e-bay from China. It's basically a layer of UV dry lacquer with a clear protective film on each side.
You peel off one side of the film, (doesn't matter which), and place it on your PCB laminate, carefully excluding any air bubbles, then pass it through a normal laminator to seal the film to the board. (I guess you could use an electric iron on a low setting with a cloth placed over the board). Along with the mask, you then place it in the UV box and expose it. (Around 60 - 75 seconds), then peel off the second protective film and develop it using soda ash as a developer, which is harmless. The film of resist that it leaves on the board is excellent - much thicker than pre-sensitised or self-sprayed positive resist.
It's very simple to create a negative image for the mask from a positive one in a matter of seconds. In 'PAINT' you select the positive image, right click anywhere on it, and an 'Invert Colour' option appears. Click on that, and everything that was black becomes white. There's an example below, of a PCB I designed for the AM/FM Converter. I always print two images in case one doesn't quite print correctly of if I need to double them up. The top two are positive images, so everything that's black will remain on the board and everything transparent will be washed away when exposed and developed. In the bottom two negative images, only the clear parts of the image will remain after exposure and developing - all the black areas will be washed away by the developer. After etching, the resist in removed very quickly by placing the board in acetone.
The only problem with the film is that if there are any bubbles laft when the film has been passed through the laminator, the resist will tend not to adhere to the copper, so after exposure and developing, you need to carefully check the board with a magnifier to ensure that there are no flaws in the tracks. If there are, they need repairing, ideally with rub-down PCB transfers. Unfortunately, Seno have stopped printing the transfers, but through the kindness of forum members, I now have enough to keep me going, though I try not to have any bubbles in the film!
I don't think it's a topic that excites the interest of many on the forum, but there have been a couple of threads on the topic this last year or so, which might be of interest to you Bob:
https://www.vintage-radio.net/forum/...d.php?t=137818
https://www.vintage-radio.net/forum/...=132065&page=2