Easy Printed Circuit Board Fabrication
(Well, at least my version of it anyway)
Using Laser Printer Toner Transfer
For many years I tried all sorts of ways to get my electronic projects to look more professional. I tried everything from “ugly” construction, perforated boards, Wire wrapping, resist pen and etchant, dry transfer and etchant etc. but nothing really seemed to be all that easy or work very well for me. Some of these methods took hours to do and sometimes you still had to place jumpers on the board. A while back I was surfing the Internet and thought I would see what articles were available there. To my surprise I came across a webpage by Tom Gootee entitled “Easy Printed Circuit Board Fabrication”. The site has all sorts of text telling of different people trying the method he described. They suggested different materials to use but I’ll tell you here about my experiences with Tom’s method and you can decide for yourself it you think it will work for you.
Things you will need:
The basic idea of this process is to:
· Scan your circuit board design and save it to your computer.
· Using your printing program on your computer, print the PC board design to scale on paper
· Cut your copper clad circuit board material to size
· Clean up the PC board material with a non-metallic scrubbing material (No Soap)
· Cut out your paper design about ¼ inch larger than the copper clad circuit board
· Place the PC board on the wood to keep from burning your table or counter top
· Place the paper PC board design face down on the PC board material
· Iron the paper using the cotton or higher setting on the iron. This will melt the design and transfer it to the PC board.
· Soak the paper and PC board in water until you can remove the paper leaving the image on the PC board
· Let the PC board dry completely
· Add the etchant solution to your non-metallic tray and place the PC board into it
· Using rubber/latex gloves lightly agitate the etchant solution over the PC board. The use of a piece of wadded up paper towel is recommended
· Once the unprotected copper has been eaten away, take the PC board out of the etchant and place in a clean water bath to stop the reaction.
Now let’s talk about the reason for this process along with the paper, home made etchant solution etc.
In Tom’s article he states “The toner in laser printers and most copiers is made mostly of PLASTIC, which resists the acid that eats away the copper that doesn't have any toner on it. Inkjet printers use INK, not toner. And their ink is typically NOT a good etch-resistor, at all. There are many methods that can be used to make a PC board. Most of the traditional methods involve applying a "mask" over the desired portions of the copper, and using an acid or etchant that can't easily penetrate the mask material to remove the unwanted copper from the remainder of the surface, although direct mechanical milling-away of the unwanted copper is also sometimes used.”
The idea is to mask the copper on the board that you want to keep and let the etchant eat away everything else.
This brings me to what type of paper to use. The idea here is to print the traces on the paper that transfer them off onto the copper clad PC board material…easily. In the article there has been quite a bit of talk as to the type of paper to use in this process. The author recommends using “Staples “Picture paper”. Here is the information on that paper:
30 sheet package:
Staples' SKU (Item Number) for the "Picture Paper" (30-sheet package): 471861
UPC barcode is: 7 18103 02238 5
Cost: $9.99 (30 sheets) at www.staples.com, as of 06/23/04.
Staples' SKU (Item Number) for the 100-sheet package is: 471865
UPC barcode is: 7 18103 02241 5
Cost: $29.99 (100 sheets) at www.staples.com, as of 06/23/04. (But he thinks he paid only $19.99, at his local Staples store.)
He goes on to say “With the Staples "Picture Paper", printing was absolutely perfect, even with long areas of very wide and very narrow traces.”
To be honest I didn’t try this paper. I used some Tektronics line chart paper that worked well the first time but I recommend using the paper Tom used to be safe. You can experiment with other paper later.
Tom goes on to say “With the Staples "Picture Paper", printing was absolutely perfect, even with long areas of very wide and very narrow traces. I didn't even run them through the fuser twice, and still had excellent (perfect) results. This paper doesn't stick to the iron, either. Press hard with the iron, for as long as you want (the more the better, it seems, with this paper; My boards actually sometimes made a "sizzling" sound as they were dropped into the hot water.).
After the boards soak for 5 or 10 minutes, you can peel off at least one layer of paper and let them soak for another 10 minutes or more. The last layer of paper doesn't ever peel off in one piece. But that's OK! You can rub it almost as hard as you want, with either your thumbs or a toothbrush, and you won't hurt the traces! [After I had made the first couple of boards using the Staple paper, I started going to the toothbrush sooner. Mine was a soft (or maybe medium) stiffness brush. But I could use circular or straight motions, pressing almost as hard as possible, with absolutely no noticeable damage to the traces.]”
Keep in mind that the “Picture Paper” should last you a while. Make all the sizing adjustment using your printer with plain paper. Once you have the correct size put in one sheet of the “Picture Paper”.
Tom makes mention that you may have to run you paper through your printer twice to get a good dark copy but I shied away from this thinking that I may not have been able to align the paper in the printer exactly the same way each time and I didn’t want the image to have shadows. You can give it a try on plane paper if you wish and see how it works for you.
Now to the Etchant solution:
As Tom suggested you can make up this solution using 1 part Muriatic Acid (the common kind that's sold in hardware stores, which is actually 28% Hydrochloric Acid) and 2 parts of Hydrogen Peroxide (the common 3% kind that's sold in drugstores and pharmacies). This etchant can etch a 1-oz board in about five minutes, at room temperature, with gentle mechanical agitation. And it's almost transparent. I mix it in a plastic tub and wear rubber gloves so I can use a balled-up paper towel to gently wipe the surfaces of the board, as it etches, which seems to speed up the etching time, considerably. (Caution: The concentrated acid's fumes would be very bad to breathe, or to have around metallic items. And the acid would be very bad to get onto anything that's not plastic.)
The Complete Procedure:
Here's Tom’s complete procedure, in detail, for those of you who have never used the toner transfer method to make PC boards, before:
He used to create the copper-side pattern with a generic drawing/graphics program. If you're just starting out, note that it would be a good idea to use a real PC board or CAD (computer-aided design) program, since it could make things MUCH easier for you, later.
Note that you need to pay attention to whether or not the pattern is drawn "reversed" or not. In my case, I draw the pattern for the bottom copper of a one-sided board as if I'm looking down THROUGH the PC board, from the component side. It's just easier for me, that way. When it's done that way, flipping the paper over for the ironing step, below, "reverses" the pattern onto the upside-down board's copper side. And then when the board is turned component-side up, the pattern on the board is oriented how it was intended to be. But when I put text on the copper-side pattern, I have to use reversed text (flipped left-to-right), for it to be readable on the finished board. [Most graphics software has simple "image-reversing" features, which usually work on just a selected portion of an image, as well as on the entire image.]
FREE PROTOTYPE BOARD PATTERN DOWNLOAD:
(10/2005): Here's a bitmap pattern for a 2"x6" prototype board that I designed. You can download it for free (for your personal use, only). Note that it's about a 540kB download.
RIGHT-click on the JPG image, below, and select "SAVE TARGET AS":
- Print the pattern, using the darkest laser printer settings (On my LaserJet 4, I use: Dithering: NONE, Intensity: DARKEST, "Raster Graphics", "Print Truetype as Graphics", and RET (Resolution Enhancement Technology): OFF). If you have a "Manual Feed" tray, such that the paper doesn't have to bend as many times, or as much, USE IT.
- Never touch the board-part of the pattern paper with fingers, or with anything else, before OR after it's been printed.
- Cut the pattern out (I use scissors), leaving at least 1/8-inch to 1/4-inch of extra paper, all the way around the pattern, and an inch or more on ONE of the shorter sides (to grab it by). Lay the pattern flat, face-up, until it's ready to be used.
- Scrub the board with a Scotchbrite or "artificial steel wool" pad (nylon abrasive pad), equivalent to '0' steel wool, usually in two orthogonal directions (with a lighter pass or '000' equivalent at the end, so it's not TOO rough). (I do *NOT* use REAL *steel* wool, since it WOULD cause RUST/oxidation, after it's embedded in the copper.)
[Note that if you have to cut the blank PC board out of a larger piece, you will probably have to use a metal file, to make sure that the edges are smooth and that they don't protrude above the rest of the copper surface, at all. A small, fine-grooved "mill bastard" file works well. [I have been told that commercially, a SHEAR is usually used to cut PC board material. I currently use a small band saw, with a fine-toothed blade, with a very small opening so the blade can't twist very much (a wider blade helps with that, too). I used to use a small hand-held reciprocating-type jigsaw, with a metal-cutting blade installed. And, before that, I used a hand-held metal-cutting hacksaw.]
The "scotchbrite" step does TWO things: 1) It removes oxidation, stains, scratches, etc, so the copper surface of the PCboard is all uniformly nice and shiny. (You might have to press very hard, for this part.) And, 2) It makes the copper surface somewhat LESS than perfectly smooth. The nylon abrasive pad makes many tiny scratches in the copper. This apparently helps the toner to stick to the copper. (Press very lightly, near the end of this part.)
- Scrub the board with a paper towel soaked with ACETONE solvent. Keep doing it until (almost) no more discoloration is seen on the paper towel. Press hard! And keep switching to clean parts of the towel.
- Lay the board (with the copper side facing up) on a rigid, flat, heat-resistant surface, such as a smooth piece of wood or plywood. Blow any dust, etc, off of it, if necessary, very carefully, and off of the pattern paper. Lay the paper pattern face down on the copper, lining it up exactly right.
- Use a regular handheld household electric CLOTHES IRON, set as HOT as it will go, i.e. the MAXIMUM temperature setting (called "Linen", on mine, just above the "Cotton" setting), with no steam.
- Place the iron on the back of the pattern. Pre-heat the whole board. i.e. Hold the iron on the whole pattern, if possible (unless the pattern is too large), for at least 1/2 minute or more, pressing firmly (see addendum, below, for pounds of force used). I usually am standing next to a 30-inch-high table that the PC board is on, and just "lean on" the iron, somewhat, during this step.
I usually MOVE the iron a little bit, after about half of the time has passed, just in case the holes on the bottom of the iron, or some other factor, might cause a non-uniformity problem.
Note that almost as soon as the iron first touches the pattern and presses it against the board, the pattern will no longer slip on the copper. So, sometimes I put the iron on a small portion of the pattern (a corner, or the smaller end of a board, usually), at first, for five or ten seconds, while I hold the pattern in position with my other hand. This prevents the pattern from slipping, just as the iron is applied, especially if the pattern paper is slightly curled, or the iron is applied too slowly, or with some lateral motion, etc etc.
- After the board is well-heated (after the 1/2 minute or more, in the previous step), I place the rear of the iron along an edge of the board (with the rest of the iron on the board), and press hard near the rear of the iron's handle. I move the iron 1/4 to 1/2 inch away from the edge and press hard again, for about a half-second to a second, and continue that way until I'm near the other side of the board (with the rear of the iron), and it gets hard to keep the iron flat against the board. Than I go back the other way (starting from the opposite edge), doing the same thing, over the same part of the board. If there are board-edges that are wider than the iron's rear edge, I make overlapping passes, with the iron's side being along the outer edge of the board, on both sides of the wide edge. I usually do this whole procedure starting from each of the four edges of the board.
- Sometimes, at this point (and periodically, whenever it seems like it might be necessary), I reheat the whole board for ten seconds or so, or more, with moderate to heavy pressure on the iron, just like at the beginning.
- I then always go over the whole board with the TIP of the iron, keeping it FLAT but torquing the iron "forward", as I go, moving either side to side on the board or pulling the iron backwards, in lines about a quarter-inch or less apart, across the whole board. But I'm careful to never let the tip "gouge" or "dig in", and never let any EDGE of the iron press against the board by itself. i.e. I always try to keep the bottom of the iron FLAT against the board, no matter what else I'm doing.
- If you see the pattern starting to show, through the paper, then you have probably done it well-enough. (Or is that just some kind of black stuff from the bottom of my iron rubbing off onto the areas over the slightly-raised pattern?)
- At the end, I usually reheat the board (with pressure on the iron at the same time, again). I also usually just press the iron flat against the board, hanging almost halfway off one side, then in the middle, then off the other side (still always keeping it flat against the board), for good measure...
- The entire heating/ironing process usually only takes between two and three minutes.
- Then, usually within five or ten seconds or so, I pick up the board (i.e grab it by the edge of the pattern paper) and drop it into hot water. [A minute or two of delay doesn't seem to matter, at this point.]
I usually use a small rectangular glass baking dish (or a sink), full of hot water (about 130 deg F or more; mine is usually about 140 deg F), letting the board soak for 10 or more minutes. [Update: I usually try to carefully peel off as many layers of paper as I can, within about two minutes, and then re-wet or re-soak the board when I get down to dry layers, or the last layer.]
- Peel off the paper, or at least the TOP layer or two. If the paper underneath is still a little dry-ish, put the board back into the water, for another ten minutes or more.
- Rub the remaining paper off, with thumb pressure (or a toothbrush or other soft brush). It's OK to rub fairly hard. But your thumbs' skin may get sore. Usually, almost all of the paper residue comes off, even off of the toner itself. So, you could SEE if there were any pinholes, etc, in the toner. (I have yet to see any defects, though, using the Staples Picture Paper.) Note that it doesn't matter if there is paper residue that remains on top of the TONER.
At this point, if something has gone wrong, you can start over and not waste the board, by washing the board with lacquer thinner (see below), to remove the toner. Then, begin again with the second (Scotchbrite) step, above.
- Use small circular motions with a toothbrush, or some other small, relatively soft brush (but not with metal bristles!), to remove paper residue from small or tight areas, and, especially, from the drill-hole "marks", and any small text. This used to be the hardest, or most tedious, part. But with the Staples "Picture Paper", this step isn't too bad, at all. And you can usually rub pretty hard, with the brush, without damaging the toner at all (unless you didn't iron it correctly). Small circles with the brush, keeping the bristles mostly un-bent, and using their tips to dig into areas that need it, seems to work well.
- Rinse the board and wipe the board dry with a clean paper towel. [Update: Now I usually wash it with soap and warm water, and then rise and dry it, just to make sure that all of the paper's residues have been removed, pretty well.]
- Make any necessary corrections, using a Sharpie or other etch-resistant marker pen. I sometimes have a couple of very small flakes of toner fall off, on about one out of three or four boards, at the most, especially if I scrub way too hard with the toothbrush.
- Don't get the etchant on ANYTHING else, especially a good stainless-steel sink(!) (or your clothing). I keep the lid loosely on the container, to catch any splashes. Don't use a metal container! And don't use any metal utensils, if you want to use them for anything else, ever again! Wipe and flush any accidental spills with lots of water, IMMEDIATELY. The ferric chloride will also stain your skin. Wash it off immediately, if possible.
- When etching is almost complete, I used to remove the board, rinse it under running tap water, and put it in a small tub of half-strength etchant (diluted 1:1 with tap water), and lightly brush the areas that still had visible copper, until they had been removed. This seems to help prevent over-etching. [Update: Now I usually just wear latex gloves and rub the board with my fingers, in the full-strength etchant tub, to remove any "stubborn" areas.]
- Wash the board in Acetone. I don't use a tub of it. I just soak a folded-up paper towel with Acetone and wipe the toner off of the board. (Note that Acetone is also bad to get on your skin.)
- If you're going to put artwork on the COMPONENT side of the board [Recommended (!), especially since it's SO EASY to do; much easier than doing the copper side.], scrub it with the Scothbrite pad, at this point, with the same method that was used for the copper side. Then do an "acetone rub", with a paper towel, until no more "dirt" comes off, as was done for the copper side. Make sure the holes are all dried out. (Tapping each edge of the board sharply on a hard surface can help to dislodge any liquid that's still in the holes. Then re-dry and allow to air dry for a minute.)
Note that the pattern has to be the drawn as the REVERSE IMAGE of what it will look like after it's applied to the board.
- Hold the board and the pattern sheet together (usually printed on the other, more-easily-removed, in front of a very bright light, to align the component markings with the holes' pattern. (If your boards aren't translucent, this method may be a problem.) Then iron the component-side pattern onto the fiberglass side of the board, using the same technique as was used for the copper side.
- Soak for five or ten minutes in warm water and then just peel off the paper. Rinse and lightly rub the very minimal residue away, dry the board (and maybe wash with liquid soap and warm water), and it's ready!
The boards made this way come out nearly perfect, nearly every time.
This page is at: http://www.fullnet.com/~tomg/gooteepc.htm