Phot Etched PCB

[BigBen]

The idea behind a photoetched PCB is pretty much the same as the photographic methods used to develop film (remember film? Back in the days before everything was digital?).
I have found some links that may be helpful:
http://www.prototrains.com/etch1/etch1.html
http://www.kepro.com/howto.htm
http://www.circuitspecialists.com/level.itml/icOid/218
The first actually meant to show the processes for making chemically etched parts (which is fascinating in itself) but can easily be understood to work for PCBs too...
The different places will mostly refer to Fluorescent or UV lamps, however I have found that most light sources (other than perhaps ambient light) does a fairly good job as long as you are prepared to take some time to set everything up in the right way. With that I mean, you need some way of creating a reproducible lighting condition. In photography an exposure strip is usually used. This strip is just a piece of photosensitive paper (PCB in this case) that is exposed for different amounts of time in different locations (by moving a light barrier across it). Since photosensitive boards are not very sensitive to light, it can take several minutes to properly expose the image (In fact, I had a setup using a single 75W bulb that required me to expose the image for over 30 minutes).
The other thing -which is the part I like most- is that using this technique will allow you to make boards without the use of a laser printer or copier (required for transfer techniques) and you also don't have to iron on the image. All you do is soak it in developer fluid (available at the above stores) for some minutes and all the etch resist lines show up, just like you drew them...

BB

[idbruce]

Big Ben

I recently made an exposure box for creating my own PCBs. Since then I have etched a couple boards, one board turned out fairly nice except for top and bottom layer alignment, and the other was a complete disaster. However there is a learning curve to everything worth knowing, and I am certain that before to long I will be making professional looking boards. After creating PCBs with other types of processes, I am now convinced that positive exposure is the only way to go. Referring to some of your comments, I would like to add a few things I have learned from reading (not by experience). As you mentioned, you can use alternative light sources besides an exposure box with UV flourescents, however the main benefit of the exposure box is the uniform lighting during the exposure time which should result in better trace consistency. In addition to uniform lighting, a quality negative is of the utmost importance for quality PCBs. I remember when I bought my HP LaserJet 6L, I was so impressed by the output. My documents looked like they just arrive from a print shop - crisp and clean. I would like to encourage anyone interested in positive developing to build an exposure box and buy a laser printer. I have not created the perfect board yet, but I can foresee it in the near future. I print my negatives on the LaserJet 6L using drafting Vellum as my paper, the Vellum allows enough light to pass through and expose the board. A homemade exposure box, an old LasetJet 6L, and drafting Vellum makes a good combination for exposing PCBs. Once I get the process down pat, I am certain that my boards will always look professionally made. For those readers that are interested in this process, don't be afraid to try it. You may not get immediate perfect results, but you will see the light! As Ben said, you can use an alternative light source, and you really don't need a laser printer. Just get started with this process and you will never go back to toner transfer.

Bruce

[PMinMO]

Personally I don't etch any longer, pcb mill...no chemicals. But for most it's a chicken or egg issue, can't mill pcb's without having working electronics first....

[idbruce]

Phil

LOL. So true. You have got to have the electronics, and of course the milling/drilling machine

Pretty soon I will have the option of doing it either way. I notice you did not mention the money you save by milling. Those darn chemicals are expensive, but I do like the output. I have never seen a milled board. I am curious as to what it looks like, trace quality, FR4 finish, etc...

Bruce

[PMinMO]

Here is a video I did for my sister website, at the end you can get the real perspective of size: http://www.millpcbs.com/phpbb3/viewtopic.php?f=12&t=13

[idbruce]

Phil

That was pretty cool. I checked out the site for a bit, it is also very informative. PCB-Gcode sounds like a nice and easy way to get things going.

Bruce