Hi Again Mike,

Single Sided boards are definitely easier to make than double sided. But you can learn to do double sided boards when needed. I've told you how to do the alignment with a common corner/edge fiducial datum on both transparencies. If you try it you will be surprised at how well the two sides line up.

As for developing and etching, time is the enemy. The longer you spend in the process, the more error you introduce. So do everything you can to speed up both processes. Start by warming the developer and the etchant. Elevated temperature makes both processes go faster.

Here's a tip on developing. What you need to guard against is overdeveloping some ares of the board while underdeveloping others. And remember, even if your etch resist is perfectly covered and exposed to uv light, all of the resist will react to the developer. The UV light only changes the rate of reaction. If you leave the board in developer long enough, all of the resist will disappear. So take care not to expose your board, even briefly, once the transparency is removed, but don't think that any part of the resist is now impervious to developing.

Put your etchant tray next to your heated/warmed developer bath and rinse sink. Working only under your safe yellow lamp, develop the board as normal. Once you've developed the board put it briefly in the etchant and remove it. You will see a change in the surface of the board everywhere the copper was exposed to etchant. This is called pickling and it will be obvious. If there are areas that were not sufficiently developed, areas that looked like the photosensitive resist was gone but where a residue remains, they will be plainly visible as "un-pickled" areas. Rinse off the etchant and ladle developer over those "un-pickled" areas with a spoon. Once all of the exosed areas pickle from the etchant, your board will etch in a nice, uniform and even manner.

If you get one or two spots where the trace developed away, or if you have just a few minor imperfections, you can touch them up with an etch resist pen or dry transfer tape. But with practice you shouldn't need to do such things (usually).

And now here's a tip for etching. In addition to heating, mechanical agitation speeds things up. An air pump (like from an aquarium) blowing bubbles that run up the sides of the board helps a lot (this assumes you have a process container that allows you to process the board vertically). Still, and as before, time is the enemy. Etch resist does not completely protect the copper beneath. As the exposed copper that is adjacent to the resist dissolves, copper just beneath the edge of the resist is exposed from the side (picture this in cross-section). So as the copper etches away farther down, the copper under the resist also begins to etch away from the sides. The net result is that you end up with traces that have a trapezoidal cross section instead of a rectangular one. And if the etching process takes too long you will eventually etch all the way across the top of the trace which means that the whole trace is now etching away. The smaller your trace, the worse this problem becomes. And the solution is to etch as fast as possible.

I can tell you that when I still made my boards this way I was able to produce 0.010" lines and 0.010" spaces (0.254 mm x 0.254 mm) consistently and repeatably. Though I never had need to then, I have no doubt that I could certainly gone smaller. No, I did not get it right the first time. I messed up my share of boards while climbing the learning curve, and it was definitely frustrating. But in the end I was able to produce a circuit board in a few hours. Compare that to when I tried to use the discount prototype shops and had to wait weeks, not days, to get a board back.

Good luck.

Joe

P.S. I too used a laser printer and transparency, but try to make certain that it is producing a completely blacked out and opaque image. And yes, holding it up to the light will work fine for this purpose. If you see lines of light in your traces, they will be transferred to your board. This might be a good time to do some of those "pen and ink" touch ups.