03/30/2007
As detailed around the net and probably various other places, home PCB fabrication can be a rapid and accurate process. I started my initial home PCB fabrication by using the old sharpie and ferric chloride technique; which involved printing an image out and then poking holes in the paper and marking through the holes to get a rough outline that would then be filled in later. Recently I've stumbled upon a much better option. Below I'll describe the process I use which involves some PC software, a LASER printer, regular iron (as in hey my shirt is wrinkled and I need to go iron it), and some etch solution.
The best process I have found is to first use some software to created a clean, precise and easily editable PCB layout. PCB/Schematic layout software such as eagle from CadSoft is where I started. The demo has a limited board size of 4x3.2, but has many libraries available and most projects fit with-in the board requirements. I have recently come across FreePCB, which is a free PCB layout tool and looks to be the way I will go soon for all of my layouts (the only problem is I don't see an easy and accurate method to export an image out of the software, at least for now). Another option is to use something like Paint.net , a photo shop like tool, which is how the DC-DC Excalibur board (pictured to the lower left) was designed.
Now the image is prepared for transfer. Bottom layouts should be non-mirrored except for the text, while top layouts or solder masks should be printed out mirrored.
Once prepared the image(s) need to be printed out in high quality on some heavy gloss paper (don't go trying to save your toner here). Let me state that I have never tried this process with an inkjet, and I'm fairly confident it will not work, I have no idea how you are going to get the ink off of the paper and onto the copper. That said, if you did manage to transfer the ink or pass your PCB through your printer, the ink supposedly won't hold up well to the etch chemicals used. A laser printer is a must, I use a brother 5250DN. Alternatively you could optionally go to a copier and copy from a regular print to the nicer paper (we'll talk about paper just below) since copiers use toner just as a laser printer does. Though for $250 it's hard to pass up an auto duplexing 1200x1200 or 2400x600 dpi networking printer.
I'm currently using Office Depot glossy laser presentation 55lb 92 bright paper for $20 for 100 sheets. It might seem expensive, but at 20 cents a sheet and the ability for me to make a PCB from printout to complete etch in 20 to 30 minutes it's a steal. I'll diverge here slightly and explain my adventure for paper, if you don't want any advice or don't like reading, then move on. I read on a number of websites that inkjet paper of some type, usually photo was best used albeit in the laser printer. I found had mixed results from nearly perfect transfers to cracked ineffective printouts I desperately tried to transfer. I accidentally purchased "Office Depot® Glossy Laser Presentation Paper, 8 1/2" x 11", 65 Lb., 85 Brightness, Pack Of 100 Sheets" although the paper is of a heavier weight 65lb vs 55lb the paper is actually much thiner and wont' transfer a damn thing, don't get it. My best result was walking up to the print center counter and asking for a few sheets of the different laser presentation papers they had. I paid 65 cents for 6 pieces of paper. 3 sheets of the office depot and 3 sheets of HP. Both worked perfectly. I had 100% transfer even the lettering came out beautifully.
Next inline, we need to transfer that image you printed out to the copper clad board. I prefer to cut my PCB to size first. A hax saw works, but can make ugly lines if you aren't careful, a band saw is the best. I recently purchased some fine toothed metal jigsaw blades and once tested I'll report back on their quality of cut. Next we need to clean all those greasy finger prints (and oxidation) off of the copper. Make sure your copper is nice and clean by using either 0000 steel wool or those green scotch brite pads, the ones that scratch the hell out of nice pots and pans, to scrub the copper with. I use acetone to wipe up between and at the end of scrubbing the copper. Make it shine, but be sure not to rub it all away, we'll be needing that for the circuit.
Once the copper is all cleaned up, take a freshly printed image and lay it onto the PCB. My Iron is set at a high cotton setting or even linen, if someone really cares I can measure the temperature and report it. The PCB should be on the ironing board copper side up then the paper should be next and finally the iron on top. Making sure the paper does not move, I press one side of the paper to the PCB and lay the iron down making an initial transfer that will cause the paper to stick to the PCB. Move to the other side and repeat. Once the paper is "tacked" down start to push the Iron down with some force and mix between going back and forth, side-to-side, and spinning. Now let the iron sit on the paper for a couple of minutes and go find a wooden rolling pin now I usually place the PCB onto the rolling pin with the paper facing up and again heat the paper-PCB sandwich rolling forward and backward, thus allowing for a greater amount of pressure-heat transfer. After doing this for a few minutes I let the iron rest on the paper and PCB and give it a few minutes. Try not to heat it so long that the FR4 (or whatever substrate you happen to have) starts to outgass (i.e. start to stink/smell/eventually melt to your ironing board; you didn't go out to buy a rolling pin did you?).
Ok, so remove the iron and let the paper PCB combo cool at room temperature until it has arrived at room temperature. DO NOT PEAK, yes it is tempting, but and lifting/pulling will damage your transfer. BE AWARE As the board cools you might notice bubbling in the paper, this is usually fine since the paper will not stick where there is no toner. A number of people have suggested that immediately after ironing, the PCB can go directly into water of varying temperatures, I haven't tried this as of yet since letting the PCB cool at room temp has worked well so far and is a rapid enough process.
Now that your PCB has cooled off plop it into a bath of cold water. I use a bowl for smaller PCBs or large plastic containers for large boards. After about 2 minutes of soaking rubbing the paper should cause it to disintegrate and be gently removed from the copper with out removing any of the trace/toner transfer. Continue the process with the board either submerged under water or being re-wet often. Ferric chloride is more picking an won't go through a paper layer and therefore must be completely removed. This is especially important between small traces and on lettering. I usually scratch lightly with a fingernail, but it should be noted that this can remove the toner if the same area is scratched too much.
If you'd like a fast etch process then all you'll need is some HCL and H202, sometimes referred to as muriatic acid and hydrogen peroxide respectively. Hydrogen peroxide can be obtained from most any drugstore at a 3% concentration. HCL can be obtained from hardware stores for concrete etching. I have found 2 gallons of 35 molar muriatic (or XX baume).
etch. TBD
