[SOLVED] Getting a good photo resist development.

[rupertlssmith]

Hi,

I etched a circuit board last week, it was a great fun and something I have not done since I was at school 20 years ago. I am (re)learning electronics.

I bought some ready treated photo resist coated boards from RS components, on FR4 base. The surface of these boards is not completely smooth, there is a noticable grain in one direction.

I think I got a reasonable exposure of the resist with a UV unit using several layers of laser printed film, 3 minutes exposure. When I put it in the developer, the exposed resist does not disappear. I had to rub it with my gloved finger quite hard in places to get the exposed areas off. Even then, due to the grain on the board there must have been fine traces left on, since little fingers of copper were left at the end of the etching, where there should be none.

Is it normal to have to scrub exposed resist off? or should the developer clean it easily away? Do I need a longer UV exposure?

Can anybody recommend some ready made boards that are smoother, no grain? Is it better to spray the resist on yourself? I suppose I can make sure I buy one made by a different manufacturer next time and see if that is any better.

Thanks for your advice.

 

[rupertlssmith]

*bump*

Anyone? Just looking for some advice on getting a good exposure for a hobbyist etching. In particular I'm unsure if I should really need to scrub so hard to remove exposed resist, or doing it wrong. Thanks for any help.

 

[betwixt]

I source boards from Farnell rather than RS but they are probably from the same manufacturer.
The exposed resist should come off completely by itself, assuming you are agitating the liquid so it gets washed away as it dissolves. It sounds like you need a longer exposure. My light box has two 8W UV tubes in it and I find about 4 minutes exposure is optimum. On occasions I have rubbed it gently if just one part seems to be stubborn, I'm not sure why that happens but I suspect the resist may have been slightly thicker in those places.

I have used spray-on resist occasionally but it is far more difficult to use. After spraying you have to keep it warm and away from dust while the paint dries and of course it can't be exposed to the light.

Brian.

 

[rupertlssmith]

Thanks. I did agitate while developing, but it definitely does not come off by itself.

Do you print your designs onto clear film? I used drafting film which takes the toner well but has a matt finish and is not a clear film. I'm wondering if I should be using clear film like is used for overhead transparency slides?

 

[Syncopator]

There's a group specialising in homemade p.c.bs at **broken link removed**
You will almost certainly find people there who have used the RS boards.

 

[betwixt]

I use clear OHP film and a Brother laser printer. The type of film isn't particularly important as long as it doesn't block UV too much. The printed side should be in contact with the board anyway to minimize light creeping under the shadow so any difference in light scatter through the film itself has almost no effect.

Brian.

 

[rupertlssmith]

Ok, I will try clear film. Thanks for your help.

 

[rupertlssmith]

To follow up and complete the thread... I tried again with clear film and it worked much better. 3 layers, mirrored so the ink side on the bottom layer is right against the board. The etched board is beautifully sharp.