|RWC Simple Printed Circuit Board manufacture|
I have also produced my own boards in small quantities, using a photo resist coating sprayed onto the copper laminate board, and I've also used a precoated board, and a UV light source. I've used the usual etch resist pens, etch resist transfers, silk screen printing of an etch resist ink, and direct machining - e.g.. milling out the copper between tracks. They all have disadvantages of some sort, and many involve another time consuming chemical process.
What follows below is a description of a method that I have used to produce prototype printed circuit boards, and it can be more reliable, quicker, and less costly than many other methods.
1) Generate the image, so that it may be printed on a normal, electrostatic, Xerox type of photocopier, or on a computer based laser printer. Many computer graphic programs can do this quite readily, or just draw it at say four times actual size, using a felt-tipped pen or tapes, etc., and photo reduce it in the photocopier.
2) Take a sheet of standard office copier labels, the sort that have the heat proof adhesive, and are suitable for laser printers or photocopiers, and remove all the labels, without damaging the backing paper. (If possible, select a sheet with a single large label since it often happens that the labels are die cut, and the backing sheet may be perforated, and it is the backing paper that we need). The back of the backing paper is ... well, like ordinary paper, but the front (the side that was covered by the labels) should have a plastic/waxy/shiny surface.
3) If you're using a computer generated image, then do a trial print onto normal paper, to ensure it prints out the correct size (Many graphic programs can be a bit convoluted in doing this, it usually helps to set the image resolution to 300 dpi, and the printer the same). You need the image to be printed in reverse i.e. looking at the final printed circuit board, the right hand edge will be the left hand edge of the print, and the tracks need to be solid black. Remember, it must be a laser printer, or else use a photo-copier. (Many of the newer printer/fax/copier machines use ink jet based technology, and these will not work for this process.)
4) Place your sheet of transfer paper (from 2) into the printer or copier so that the image is printed onto the shiny surface. This works fine with my HP Laser printer, and also with the Sharp photo copier.
5) Ensure you have a clean, grease free piece of PCB, it may help to roughen the surface slightly with glass paper or emery paper, but it needs to be very clean - absolutely no finger prints. Vim or other similar domestic abrasive kitchen cleaner is also quite good at cleaning PCB's, since it leaves a suitably roughened surface, but be sure to wash off any residues. Place the printed circuit board (copper face up) on a pad of paper (about 0.25 inches thick is OK). Place your print face down on the copper sheet. Using an ordinary domestic clothes iron, set to hot (cotton or linen), gently iron the back of the paper to transfer the image image from the paper to the copper. Do not press hard, or the tracks will thicken.
If the result is patchy, clean off the ink thoroughly, run off another print, and try again. You can re-use the same transfer sheet a number of times if you are careful. After a few attempts you will find how easy it is - provided the copper is absolutely clean. It is quite possible to produce fairly fine tracks in this manner, and if the transfer process goes wrong, it is easy to repeat, without wasting copper PCB.
6) Etch the PCB in hot Ferric Chloride or other etchant in the normal way.
7) Other uses - obvious stuff like transfers to tee-shirts, etc., or indeed transfer the component layout onto the PCB. You can also print text, lay over a strip of 'Sellotape', peel off the tape, taking the letters with the tape, and apply the resultant label to wherever the Sellotape will stick.
©Ray West 1999