Up to this point I've been using Press 'n Peel Blue to transfer the layouts to blank copper clad board. This is great for basic one-off circuits that aren't too complex. However, for the number and complexity of circuits I was getting into, I was getting real tired of the board prep, ironing to transfer the layout, and clean-up. I've read that a laminator works well instead of ironing, but decided I'd try stepping it up to the next level: optical transfer. I was a little apprehensive about trying this method, but bit the bullet, went to Home Depot to pick up a fluorescent fixture and UV tubes and got some pre-sensitized PCB and developer.
Instead of printing the layout onto Press 'n Peel and then ironing it to transfer onto the board, the optical method works by printing the layout on clear film, then laying that film on the pre-sensitized board (sandwiched with glass to keep it flat) and exposing with UV light. Developing then lets the areas that were exposed to the UV to be washed away, leaving the areas that were shielded by the printing behind to act as an etch resist. Then the board can be etch like normal. The pre-sensitized board doesn't need any prep, just have to remove the protective covering immediately before exposing.
I did an exposure test on a small strip of the pre-sensitized board to determine a good exposure time (method I learned from doing darkroom photographic printing from film), and then etched my first circuit (a test board for some of the control logic that I'll discuss in the next page). This worked out great. There's enough latitude in the exposure that it makes the process very easy, and the results were very clean and crisp, much neater and allowing smaller detail than I was able to achieve with PnP, and with much less work. I may never use PnP again as long as I have pre-sens board and developer handy.
So now, back to the design...