Step 1: Create Your Design
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
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
Step 4: Attach the Mask to the Blank Board
Step 5: 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
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
Step 8: Clean Off the Mask
Step 9: Apply the Silkscreen Layer
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
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!
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).