Inexpensive Printed Circuit Boards By - lawrence mazza ----------------------------------------------------------------- After I design a circuit, I like to fabricate it using a printed circuit board because a board offers a lot of advantages. For one, the solder connections are more stable, and for another, well, they look so nice that you want to show them off. There are several ways to make boards including etching, direct plating and copper removal. For the hobbyist, etching is probably the easiest and most cost effective. Etching is the process of chemically removing the unwanted copper from a plated board. You must put a mask or resist on the portions of the copper that you want to remain after the etch. These portions that remain on the board are the traces that carry electrical current between devices. This article will discuss an alternative approach to placing the circuit pattern on the copper clad board. One way to put a pattern on the board is the direct draw approach. A resist pen is used to draw the circuit onto the copper surface. The pen deposits an ink that resists the etchant thereby creating the desired circuit on the board. This is the quickest way to get a circuit pattern on the board, but it is difficult to position the traces accurately, especially if you are using any IC packages in your design. Plus, since the ink doesn't apply uniformly, there is a risk that the traces will be etched away since the etchant can get to the copper through an extremely thin layer of resist. Another approach is to use a photo sensitive resist. In this case, a board is covered with a resist material that sets up when exposed to Ultra Violet light. To make a board this way, you must make a photo negative of the circuit which is clear where you want a circuit trace, and opaque where you don't want a trace. After the photo negative is made from your art work, it is placed onto the photo sensitized board, and is exposed to the UV. The UV light transmits through the clear portions of the negative and cures the photo resist. After that, the board is submerged into a developer bath that develops the traces on the board. The resist that is left is in the shape of the art work that represents your circuit. The advantage to this approach is accurate and neat traces, and once you make the photo negative, it can be used over and over to make additional boards. However, you need a photo lab to do this, and the entire process takes quite a bit of time. Now that laser printers are affordable to the common folk, creative people have developed methods of using them to produce the resist pattern. One method uses a specially coated paper and is sold through many electronics outlets. The circuit pattern is printed onto this paper and the paper is ironed onto the copper clad board. The board and paper are placed into water, and after a while, the resist pattern lifts off the paper. This process works a lot like putting decals on model cars, planes and boats. And although I have had mixed results using this paper, it can also be used to make custom decals using a color printer. I have experimented with other types of paper in search of a replacement for this process. In doing so, I have discovered another, fairly consistent paper that I now use to make all of my printed circuit boards. This paper is similar to what is used in magazines. It is a white, glossy paper that prints well and costs about three cents per sheet. What makes the paper glossy is also what makes it work in this process. And although it doesn't work exactly like the 'decal' type paper, I find it just as easy to use. The reason the paper is glossy is because it is covered with clay. I'm not sure how it's made, but there is a fine layer of clay that is pressed or worked into the surface of the sheet. You can find this paper at office supply stores - just ask for 80 pound coated paper. After the pattern is printed onto the paper (I use AutoCad to draw the circuit, by the way), it is ironed onto the copper clad board using a hand iron set to maximum temperature with no steam. This process melts the toner and allows it to stick to the copper. Note that the copper board needs to be very clean in order to make the toner stick (this is true of the decal paper as well). The ironing process only takes a few minutes, and it helps to keep heavy pressure on the iron to keep the toner in contact with the board. When the board is cool, it is placed into hot water just like the decal stuff. Little by little, the paper saturates with the water, and starts to disintegrate. With a little work, you can gently rub the paper off, and what's left is the toner resist, with a little of the clay also attached to the toner. It is the separation of the clay from the paper that allows the toner to remain on the board. In the picture, you can see the white clay that is still attached to the toner. At this point you can examine the board and fix any holes or cracks using a resist pen. Then the board is etched with Ferric Chloride or Ammonium Persulfate as usual. This is just another approach to making PC boards that I find the easiest and most cost effective. Try it the next time you make a board, and let me know your experience. -L ----------------------------------------------------------------- When I started teaching Electronics, one of the most challenging things I ever had to experience was producing Printed Circuit Boards. In fact, it was so frustrating, that I contemplated getting out of Electronics altogether. But now, there is a new way! I call it The Toner Method. Photo Resist never worked for me. Heinous is a good word to use. The Etch Resist Pen was expensive - $10 a pen, and they always went walking. Masking Tape worked for simple, non-IC circuits, but it was tedious, and poor quality. Plotters are finicky, use up pens and take forever and a day. Mesmerizing to watch. Definitely "High Tech." The Toner Method is incredible! It is the greatest thing since Roswell! All you need is a PCB design program (such as PCB Wizard, or even AutoCAD or AutoSketch), a Laser Printer, and Photo Quality Ink Jet Paper. The results are Laser Quality, Reliable, Inexpensive, and No Nasty Chemicals! Design the PCB (component side), check for errors Laser Print the PCB onto the clay side (whitest) of Photo Quality Ink Jet Paper Thoroughly Clean the copper board (I use super fine steel wool, then citrus cleaner) Place the paper Toner Side Down onto the copper Iron the paper on high heat (Cotton Setting) with pressure and steam for 40 seconds, pressing 10 seconds in four different directions. Run the tip or edge of the iron over the paths Allow to cool thoroughly. Gently peel the paper off, the toner should be left behind! Touch up any damaged or missing traces with a Sharpie (or equivalent) pen. Etch And you're done! Easy! Nice thing is, the students can print the image, and prepare the board at home. It may be a good idea to print the image at least three times on one sheet. This makes printing easy, plus allows for at least two mistakes. The sheets cost $0.25 each (generally), a fee most students can foot. Any slick photo-quality paper found where you get printer supplies should work. My biggest hints are 1) Don't rush the ironing prosess; I don't think that you can over-do it. 2) Use very warm water to soak off the paper--again, don't get in a hurry-- 3) Brush the exposed side of the paper vigerously to remove the clay then put it back in to soak. I also use a flat-edged Xacto knife to remove some of the larger areas between traces and increase absorption. ----------------------------------------------------------------- From: tomg@fullnet.com Newsgroups: sci.electronics.cad Subject: Economical and robust PCB toner transfer paper Date: Thu, 20 Jul 2000 07:19:59 GMT I've recently tried many different paper types, and have found one or two that give excellent results for making PCBs (printed circuit boards) via a laser printer and the clothes iron toner transfer method. I tried almost every glossy paper type that our local Staples office- supply store carries, plus the "house glossy" from our local printer. Most either had "pinholes" in the large black areas, or in the vertical (to the print path) areas, or had removal problems after ironing. For example, the HP Premium Photo Paper had perfect printing, no pinholes at ALL. But, it was almost impossible to remove, even with long soaks in soapy hot water, or in alcohol, and sometimes pulled the traces off with it. Anyway, I finally found a good paper that's always free of pinholes and still removes fairly easily. It also leaves extremely strong toner/traces, which can be scrubbed fairly hard with a toothbrush, or rubbed very hard by fingers, without being damaged. It is the JetPrint "Graphic Image Paper, Gloss Finish", Heavy Photo Paper. They also make a product called JetPrint "Multi-Project Paper, Gloss Finish", Medium Weight, which almost falls off the board after soaking for 10 minutes. Alas, it sometimes has pinholes. (I use an HP LaserJet 4. Your mileage may vary...) However, the Multi-Project paper IS PERFECT for doing the component sides of circuit boards, and anything else where etching isn't required... Here's my procedure, for those of you who have never done this before: - Print the pattern, using the darkest printer settings. Cut the pattern out, leaving at least 1/4-inch all around. - Scrub the board with a Scotchbrite 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 don't use real steel wool, since it may cause rust after it's embedded in the copper. - Wash the board with liquid dish detergent, then with acetone, then with alcohol, drying with a new paper towel after each, and never touching the board surface with fingers after the first wash. - Lay the board on a paper towel, copper side up. Blow any dust off of it, carefully, and off of the pattern paper, and lay the pattern face down on it, lining it up just right. - I use a regular clothes iron, set as hot as it will go ("Linen", above "Cotton"), with no steam. - Place the iron on the back of the pattern, for about one minute, pressing very firmly, moving it by 180 degrees at the half-minute mark (just in case the holes on the bottom might cause a problem). (Note that if you try the HP paper, you better put a sheet of regular paper between it and your iron, because it will stick to the iron!) - After the board is heated (after the one minute), 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. I move the iron 1/4 to 1/2 inch away from the edge and press hard again, for about a half- 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. When I reach the other edge, I go back the other way, doing the same thing. If there are board-edges that are wider than the iron's rear edge, I make overlapping passes with the iron's side against the outer edge of the board, on both sides of the wide edge. I usually do this starting from each of the four edges of the board. - Sometimes, at this point, I reheat the whole board for ten seconds or so, or more, with moderate to heavy pressure on the iron. - I usually 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, or by pulling the iron backwards, in lines about an inch apart, across the whole board. But I'm careful to never let the tip gouge, and never let any edge of the iron press against the board. I always try to keep the bottom of the iron flat against the board, whatever else I'm doing. - 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 whole heating/ironing process takes between two and three minutes. - Then, within five or ten seconds or so, I pick up the paper towel, with the board on it, and hold it under cold running tap water for 15 to 30 seconds, to stabilize the toner. I turn it over and cool both sides. - Then I immediately place the board into a sinkful of hot water (about 130 deg F), for 10 to 20, or more, minutes. - Peel off the paper, or at least the top layer. If the paper underneath is still dryish, put the board back into the water, for another ten minutes or so. - Rub the remaining paper off with thumb pressure. It's OK to rub 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, though, using this paper!) - Use small circular motions with a toothbrush, to remove paper residue from small or tight areas, and from hole marks. This may be the hardest part. I will soon try leaving the residue IN the holes, to see if the etchant can work through it. - Rinse the board and wipe the board dry with a clean paper towel. - Sometimes I wipe and rub the board with a paper towel and 70% alcohol, especially if it needs correction-pen marks. - Make any necessary corrections, using a Sharpie or other etch- resistant marker. 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. - Etch. I use Ferric Chloride, in a tupperware plastic bread container, in a sink of hot water, agitated by an old metal record- player turntable turned on end, with a bolt an inch from the spindle attached to a small piece of wood that is also attached to a bolt that protrudes near the plastic container's top edge. I have a couple of bricks in the sink, to keep the container in line side-to-side as it's rocked front-to-back. I usually use either the 33 RPM or 45 RPM setting. (Don't get the etchant on anything, especially a good stainless-steel sink!) I keep the lid loosely on the container, to catch any splashes. If you use 1-ounce boards, instead of 2-ounce, etching is much faster, and, correction-pen marks will last long-enough to work well. Plus, over-etching isn't usually as much of a problem. - When etching is almost complete, I usually remove the board and put it in a small tub of half-strength etchant (diluted with water), and lightly brush the areas that still have visible copper, until they have been removed. - Wash the board in laquer thinner, rubbing with a paper towel, to remove the toner instantly. But be careful! I do it outside... - Drill. Some people have suggested drilling BEFORE you etch. OK. But I like the way the etched hole marks help guide my drill bit into themselves, especially on small pads and when holes are very close together. I use a regular floor-standing drill press. I have tried the pure-carbide bits, about .035 inches, with the larger shanks. But they are so strong they're too brittle, and they break too often, for me. (Even getting 50 of them for $5 at a hamfest doesn't seem like a good deal. That's how often I break them!) So, I usually just get the "wire-gauge" high-speed steel bits, from the local hardware store. I've been using the #60 (.04 inch), since they fit a large variety of component lead sizes (all but the largest). I got 15 bits for about $20. I change bits every few hundred holes, at least, or whenever I notice the edges of the holes are getting pulled away from the board too much. I guess the FR-4 board material doesn't transmit heat well at all, and the steel bits get hot quickly, and consequently dull quickly. To hold the tiny bits in my large drill, I bought a small chuck that fits into my larger chuck. - If you're going to mark the component side, scrub it with the Scothbrite pad, at this point, then wash the board in soap and water, and then 70% (rubbing) alcohol. Make sure the holes are all dried out. Hold the board and pattern up to a bright light, to align then component marking with the holes' pattern. Then iron on the component- side pattern, but using the other, more-easily-removed "Multi-Project" paper, mentioned above. Soak for five or ten minutes in warm water, then just peel it off. Rinse and rub the very minimal residue away, dry the board, rub it with a paper towel with alcohol on it, dry it again, and it's ready! If anyone's interested, I can try placing the board on a scale, and see how hard I'm actually pushing, with the iron. The boards made this way come out nearly perfect, nearly every time. Well, I tried leaving the paper residue IN the holes and etching. But the result was less than satisfactory. So, in order to minimize the potential for damage to the traces from hard rubbing with the brush, I tried letting a board soak overnight in water. Voila! The drill holes were easily cleaned out with fairly light scrubbing with the toothbrush. Of course, I usually can't wait overnight. Adding some liquid dish detergent helps, if I'm in a hurry. Also, digging the bristles on the tip of the brush straight into the holes, while making tight circular motions, gets the residue out with minimal brush pressure. It is still quite tedious, if there are lots of holes, though. Also, I DID put a bathroom scale under the iron, and simulated pressing on a board. I was using at least 25-30 LBS of force. I don't know how many PSI it is, because I use the same force on boards sizes of 4X6 inches and of 2.375X6 inches. Both seem to come out equally well. I have, several times, used a lot more force on the iron, and it IS possible to flatten out or blur pads or traces, if I press hard enough, or if I accidentally scrape with the edge or tip of the iron instead of keeping it flat. Someone else suggested baking the boards in an oven, after the toner has been applied and before etching. With my current paper and method, I don't see why it would be necessary, since the toner seems so strongly bonded to the board. However, back when I was using paper that left pinholes in the toner, I wanted to try baking a board just to see if the pinholes would close up. At the time, it also seemed like heavier iron pressure might close them. But it never seemed to. Now that I'm using the JetPrint Graphic Image Paper, I don't need to worry about these things any more. Happy board-making, everyone! Tom Gootee Gootee Systems