Step 1: Create Your Design
Start out by laying out the PCB traces & pads with your favorite CAD or PCB design program. I used Pad2Pad, mainly because I found that program pretty easy to use, and it's free for download. You're supposed to use Pad2Pad to design a board, then send the file to the company for manufacture. Instead, I use this design to create my own etching mask.
Unfortunately, you can't export p2p files into other formats. So, I printed the board layout to a PDF, then opened the PDF into Illustrator, which allowed me to clean up & fine-tune the design and separate it into layers. This technique is for creating single-sided PCBs, so I made two masks: One for the copper traces & pads, the other for the silkscreen. You need to print out a mirror image of your masks -- you'll see why soon -- but because the traces go on the back of the board, you can print those out normally. The silkscreen mask should be printed out in reverse.
I use 2pt lines for most of the traces; that comes out to about 0.028".
Step 2: Print the Masks
This is a tricky step. You need to print the masks onto special paper, and make them as dark as possible. Here's how I did it. I used Jet Print Multi-Project glossy photo paper. I had to order it online, but it might be available at larger office supply stores. Tom Gootee recommends Staples "Picture Paper"; that seems easier to obtain. Unfortunately I didn't read Gootee's article until AFTER I'd already gotten the Jet Print paper. So the Staples paper might be better.
These papers are marketed as ink-jet papers. But for this process, you need to run them through a laser printer. The toner creates the mask. And, you want the toner to be as dark and dense as possible. I found that if you tell the printer that you're printing a transparency, it'll apply more toner. I also adjust various settings on the printer menus (e.g., toner density, optimization, etc.) to get the densest possible print -- your printer settings will vary. Experiment to see what works best, and take notes as you go so you'll be able to duplicate your best efforts later. I burned through quite a bit of paper before I got it right, but now I get it right the first time.
If your PCB design has long vertical traces, you might orient the design on the page so that the long traces are angled. Because of the direction that paper travles through laser printers, long vertical traces might lose toner density near the bottom. Angling the long traces helps keep the toner dense on the full length.
Remember to print the copper mask "right-reading" -- i.e. NOT a mirror image -- but the "silkscreen" mask shold be printed in reverse.
Make a print or two and find a mask that is uniformly dense with a minimum of pinholes. Make sure all the traces and pads are complete.
Step 3: Prepare the Blank Board
Cut your board to size, leaving a little extra room around the edges. I use a hacksaw, which leaves some burrs. Smooth any burrs off with a dremel or small file. You want the copper surface to be as flat as possible. Sand the surface of the blank board with 400-600 grit sandpaper in both diagonal directions in a crosshatch pattern. Then, use acetone on a paper towel to clean the board as thoroughly as possible. Grease spots are your enemy! Scrub the board really well.
Step 4: Attach the Mask to the Blank Board
Carefully cut out the mask for the copper side from your printout. Place it face-down onto your board, so that the toner faces the copper. I use tiny bits of scotch tape on each edge to hold the mask in place. That might not be necessary if your blank is somewhat larger than your mask. I found that the mask tends to slide if it's not securely taped; you want to avoid that when working with tight tolerances.
Step 5: Iron!
This is the trickiest step. You need to set your iron to its highest setting, no steam. Lay a paper towel over the board & mask; otherwise, the sticky melted plastic that oozes out from under the edges of the mask will cause the whole thing to stick to your iron.
When first applying the iron, press straight down and try not to wiggle or slide the mask. The plastic surface layer of the paper will melt instantly, forming a temporarily slippery layer, which will tend to slide around if you're not careful. This is where it's easiest to screw up, I think.
Start by applying steady, firm pressure to the whole board for one minute, moving the iron occasionally to make sure that the whole board is heated thoroughly. After that, the mask is pretty much stuck to the board, so now you can go over the whole board with the edge of the iron, a little at a time. I use the edge of the iron & lean on it some, putting good heavy pressure lengthwise along the board. Then I move the iron a quarter inch or so and repeat until the whole board is covered. Then I do the same series of "pressure lines" widthwise across the board. Finally, I finish with overall pressure for a few more seconds. The total ironing time is maybe 3 minutes, tops.
Step 6: Soak Off the Paper
Drop the hot board immediately into a pan of hot water, along with any of the paper towel that might be attached. Some of the paper will start to come off right away. Help it along! After a few minutes, more paper can be pulled off. Also peel off any scotch tape you used to hold the mask to the board. After 10-20 minutes, you'll be down to the last layer, which is more like plastic than paper. The traces will be clearly visible though it. Get a corner started, and the plastic should peel off easily, leaving you with a nicely masked board. If you've ironed well enough, the toner will be fused to the board solidly; it can't be scraped off with a fingernail.
If the traces are messed up in any way -- for example, if the iron slipped -- you can clean off the fused toner with acetone and start over with a fresh mask.
Step 7: Etch
Drop the board into your etch solution. Don't let the etch chemical get onto anything made of metal! I use a large plastic containter. Etch the board until the remaining copper is gone. Depending on how fresh & warm the etch chemical is, it could take 10-30 minutes.
Step 8: Clean Off the Mask
Use acetone to clean off the toner. You'll be left with a nice shiny circuit board!
Step 9: Apply the Silkscreen Layer
Now it's time to add the "silkscreen" to the other side of the board. It's not really a silkscreen; it's actually the same process as described above, except that you leave the fused toner on the board and don't do the etch and cleanoff.
To align the "silk", I drill a hole in the four cornermost pads. After cutting out the silk mask, I place it toner-side-down against the side of the board opposite the traces. Holding it up to the light, you should be able to see the four corner holes through the mask. Use these to line up the silk mask properly, then tape it to the board with scotch tape. Next, iron the board the same way you did the copper side, and finally soak off the paper as in step 6.
Step 10: Drill the Holes
This is a little tricky, but can be done without requiring a drill press or other fancy equipment. I use a dremel tool with a #60 bit. That's the smallest bit I can find at the local hardware store. The bit is clamped into a collet, which in turn is held in the dremel's chuck.
Here's my secret to drilling lots of tiny holes with a hand-held drill: use a scrap piece of acrylic as a drill guide. Drill a hole in the acrylic, then drill through that hole and through the board. The clear acrylic makes it easy to line up the drill bit correctly on the center of each pad. After a dozen holes or so, the "guide hole" in the acrylic will start to "loosen up" -- just drill another guide hole & keep going.
Step 11: Finished!
The board is ready to use.
I've made four boards using this method. The first one was perfect, but got ruined by sloppy soldering. The second and fourth were also perfect & worked great in projects. On the third board, I moved the iron when I first applied it, so the mask slipped and blurred some traces.
With a little practice, you can make a board in a couple hours (not counting design time).
HavocRC made it!