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by Dave Eisenstein This article is NOT about designing a PCB from scratch, with the routing problems of the circuits and layers, plus double-sided, etc. It is how to make a simple PCB you found already drawn in a book, magazine article or over the internet. First, you really may not need a PCB at all for your projects. Heresy! If it is simple enough, you may use pre-perforated "vero" board. That creates the problem of adding a bunch of wires to connect your various components. Additional heresy! You may not even need a board of any kind...see Georg Ziegler's boardless DCC decoder accessed from page 2 of http://home.freeuk.net/merg/resources/index.htm For most of us, one or more printed circuit boards are the way to go. You can sometimes buy the ones you want from a fellow modeler, such as Dick Bronson, with a Block Occupancy Detector (BOD) that he had made up for himself, and is now willing to sell: http://www.rr-cirkits.com/index.html If you want to make 50 or more of your own devising, then there are commercial sites. Veteran modeler Mike Dodd of Montpelier, VA says he has good luck with WWW Electronics -- E-mail at wwwinc@esinet.net. Dick Bronson likes Excel Electronics, found at http://www.excelnc.com It seems that (aside from drawing your own with a resist pen) there are several ways to go such as photo-resist laminated to copper applied to various non-conductive bases, such as glass laminate. Kepro Circuit Systems of St. Louis, MO sells "bare brass" to which you add the dry film resist which they also sell, or various combinations of already applied photo-resist on the copper coated board, sold in 1 oz or 2 oz versions. http://www.kepro.com Their photo-resist only works with "negatives"; they sell special film to make the negative. TIP!Of course, a positive drawing can be made on a transparency (next paragraph) and used with heat fusing the toner directly onto the bare copper board, then etched. No "negative" inversion needed. You may need to "flip" the drawing, by using "Reverse" option in your graphics program. On the other hand, MG Chemicals makes a kit "416-K" that uses a "positive" photo-resist on three boards, 3"x5", 3"x6", and 6"x6", with trays, chemicals, rubber gloves, and instructions for about $30.00, from FAI Electronics, 10977 Granada Lane, Overland Park ,KS 66211, at 913-498-1531. MG sells an "exposer" kit with UV. However, the sun can be used as the "exposer", but suggest being careful, the traces must be dark. MG has a nice demo, instructions and a FAQ on "How to Make a Printed Circuit Board" found at http://www.mgchemicals.com/T3_Demo.html and ..../T3_Instructions.html and ..../T3_FAQ.html To copy the PCB drawing from an article for use in making a PCB, try transparency film as the "paper" in a photo-copier or laser computer printer that uses toner fused with heat. I used Apollo Laser Printer Transparency Film CG7060 from Office Depot. Or use NewsCraftLGN (for Laser Generated Negative) for this purpose. They are found at: http://www.systemfacilities.com/products.htm as suggested by Randy Gordon-Gilmore, a railroad modeler, who wrote at length about his extensive photo-etching experiences at http://www.rickadee.net/~zephyrus/etch1/etch1.html and again at .../etch2/etch2.html Another source is sold as a Toner Transfer System with all the works (machines for each step!) at http://www.dynaart.com/C.Direct_Etch.html For a brief overview of all methods possible see their interesting write-up at http://www.dynaart.com/B.Techniques.html Theirs is an "iron-on" system at its heart. [Craig Sutherland of Kansas City suggested this.] One problem with photo-resist is the need for another chemical to remove the photo-resist not exposed to light (negative) or to remove the photo-resist exposed to light (positive), so as to develop the image made with ultra-violet light (or the sun at mid-day) thru the film. Then, as usual, the etching of the copper (or brass) still needs to be done with ferric chloride. "Yep...you pays your money and you makes your choice." The developer chemical is a 1% solution of sodium carbonate (Arm and Hammer washing soda). The etchant is ferric chloride and will stain your clothes and hands so use rubber gloves. Another etchant is sodium persulphate crystals (unlimited shelf life when dry) but very limited shelf life after mixing with water. Both etchants need handling with care. Sodium hydroxide (lye) could be used to remove the hardened resist after etching, but is considered difficult by some persons. Some resists can be soldered right through without removing. MG Chemicals says theirs is the latter. A 1991 article in Model Railroader suggested heating the PCB copper board at 275 degrees F. in your kitchen oven, then ironing on the fused toner image from your paper or from film, protecting the film from the iron with paper to prevent the film from crinkling. Some like the ironing method; others the photo-resist. To give you some idea of the cost of the boards and chemicals, here is a recent price quote by Circuit Specialists, Inc. found at http://www.web-tronics.com/
Another modeler wrote on "making PCBs at home" from Australia. Catch his most interesting comments at http://www.users.bigpond.com/pbhandary/misc/MakePCB.html He uses pre-coated PCBs, exposes them to UV (ultra-violet), then develops and etches. His approach is different from most, but he gives extra good advice about choosing drills. We appreciate his findings at the URL given above, from Prashant Bhandary. Randy Gordon-Gilmore suggests the possibility of using baking paper (used for lining cookie sheets) because it has a silicone coating that will act as a "release agent" to the toner fused on it by the laser printer. He further suggests always using distilled water to avoid the local contaminants found in the water of some cities, when mixing chemicals. Nearby Kansas distributors for Kepro are given as Carlton Bates Co. 9214 Bond, Overland Park, KS 66314, at 913-438-4848; and Newark Electronics, 6811 West 63rd St., Overland Park, KS. 66212, at 913-677-0727. They sell kits from Kepro for hobbyist's use:
Radio Shack also sells a small kit for about $15.00, with two small boards, trays, etc. These are bare copper boards with no photo-resist. However, that means you can use the positive transparency (reversed first) directly on the board with "ironing" heat alone, then etching with ferric chloride in their tray, rinsing carefully as usual. Another UK modeler, Alex Chambers, for UV (ultra-violet) exposing, uses a face-tanning UV unit to expose photo-resist laminated to his bare copper boards. He laminates the photo-resist to his boards with his office laminator set at its lowest heat setting (about 90 degrees C).
Finally, Herbach & Rademan of Mt. Laurel, NJ, often have good buys on some of these things. Try them at http://www.herbach.com for their complete catalog.
IF you have questions on the techniques outlined or the vendors mentioned (or most anything else) in this article, feel free to contact Dave Eisenstein directly. He's a very agreeable and knowledgeable chap, and will do his best to answer any question you may have.
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