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– An irresistable way to make PCBs at home! Ever wished that there was a way to transfer complicated PC board artwork from a magazine without having to resort to messy (and expensive) techniques such as photo-etching? Well, you can do it using nothing more complicated than a photocopy or a laser printout and an iron! By Heath Young I f you have ever used 3M’s “Dalo” pens for doing PC board artwork you will pretty soon realise that they have their limitations. The quality of the tracks you can produce is dependent on how steady your hand is and when the time comes to etch your board, you will discover that the pen is not quite impervious to all aqueous etchants. I have thrown out many a board due to severe pinholing in the tracks when I have used ammonium persul-phate etchant. The procedure that I have now come to use almost exclusively, even for small boards, is a method known as toner transfer. This uses the toner from a laser printed or photocopied page as the resist material. Toner is made from colourant (carbon black, etc) and a low melting point plastic. The plastic is impervious to aqueous etchants, so pin-holing should not be a problem. The question is, “How do you get the toner off the printed page and onto the copper laminate?”. It’s done by remelting the toner while it is in intimate contact with a very clean, slightly roughened PC board. You’ll need an iron To melt the toner, you need to beg, borrow, buy or steal an iron. No, not a soldering iron – the iron used to press clothes. Step 1: print a “reverse direction” PC board pattern with a laser printer or photocopier. You’re looking for dense blacks and no break-up in the pattern. 72  Silicon Chip A tip: don’t tell anyone what you are going to use it for otherwise they might not let you have it! Tell them you’re going to iron a shirt (on second thoughts, that’s not such a good idea – they’ll certainly not believe you!). While the iron is used to melt the toner onto the black PC board, done correctly this won’t harm the iron. Artwork preparation There are a lot of different printer papers and a lot of different toners around. So some experimentation may be necessary but the basic method remains the same for all. Firstly, you must get your artwork – this must be the mirror reverse of the track outlay. The PC board Step 2: clean the slightly oversize blank PC board thoroughly then slightly roughen it with 600 wet’n’dry. Avoid touching the copper surface once clean. artwork for projects printed in SILICON CHIP must be mirror reversed (inverted) before they are suitable for toner transfer. This is actually simpler to do than it sounds and can be done in a couple of ways. A good quality photocopy of the artwork can be made onto an overhead transparency sheet and this- sheet is then flipped and photocopied again onto paper. (Note that the photocopy of the transparency has to be done so that you can read the lettering when it is placed on the glass – otherwise you will get an inversion of an inversion - not what is wanted!) An even easier method, though, is to download the PC board file in either EPS or PDF format from the SILICON CHIP website (www.siliconchip. com. au) and simply tell your laser printer to print a negative (also sometimes called “inverse” or “reverse”) which can usually be selected as part of the printing process. If you are using programs like PCB Designer 1.0 or Easytrax (which may be downloaded from the ’net for free) then you will probably have designed a board in “mirror reverse” anyway, as it is much more intuitive. Mirror image boards (as if you are looking through them from the component side) are much easier to produce as there is no messing around reversing the pins when designing the board. The importance of a good quality laser print-out or photocopy cannot be over-emphasised. It must have good dark tracks, without any breaks or bridges which will obviously cause you grief later. Once satisfied with your printed image, you are ready to move on to the next step. Copper laminate preparation Cut the board slightly over-size, as the toner does not transfer well very close to the edges of the copper laminate. About a 3-5mm margin is safe (even more if practical) – the extra material may be trimmed off later. The copper laminate must be prepared before the toner can be applied. The toner requires a roughened surface otherwise it simply will not adhere or ‘key’ to the copper surface and will come off while etching. The board is cleaned up and roughened with 400 grit silicon carbide paper (“wet and dry”). Roughen the board by swirling the sandpaper (wet) in a light, circular motion taking care not to remove too much copper or the tracks will be too thin. Wash off all of the grit and dry the board with a lint-free cloth – a clean linen tea-towel is ideal for this. Do not touch the copper with your fingers from now on as the oil in your fingers may stop the bonding between the toner and the board surface. Toner transfer Cut the prepared artwork so that there is a border of about 10-15mm around the edges of the circuit board pattern. Now cut the corners off the artwork at a 45° angle – this will allow you to fold and tape the edges without creasing. Centre the artwork, toner-side down, onto the copper side of the circuit board and fold the artwork over the edges onto the non-copper side. Tape the longest side first, with Sellotape or similar adhesive tape. Don’t be tempted to use masking Step 3: cut the page out with a 10-15mm. border, then cut the corners off at a 45° angle (not too close to the artwork!). Fold the longest edge over 180° 10mm from the pattern. tape as its glue will melt from the heat and the artwork will shift and destroy your good work by smudging. The rest of the edges of the artwork are then taped onto the board, keeping the paper as tight as possible. It’s a bit like covering a book. Once you are satisfied that the artwork is well secured to the board, set the iron for the maximum temperature (ie, the “linen” setting) and turn the steam off. Put the board on a firm, flat surface (one which will not be damaged by heat!) and run the iron over the whole of the artwork. Apply a reasonable amount of pressure while you are doing this. The paper will scorch and go brown when the board is done properly and the sticky tape on the reverse side goes yellow from the heat. If you keep the heat on for too long, the copper may delaminate from the substrate – you can see this as a blistered copper surface and a discolouration on the other side of the board. Warning: the copper does get very hot! Once this happens, stop heating the board and allow it to cool naturally – do not quench in water! When the board is cool enough to touch, you will notice that the paper appears to be bubbling up from the board. This is normal with boards with wide track spacing and means that it is time to remove the paper. Removing the paper The paper is removed from the board by running it under a cold water tap and, when it is well and truly soaked, gently ‘rubbing off’ the paper fibres with your thumb and forefinger. Patience is the key here; do not be tempted to use anything harder than Step 4: wrap the folded edge over the PC board (toner to copper) and sticky tape it to the other side (not masking tape). Then tape the other three sides, stretching the paper as you go. FEBRUARY 2001  73 your fingers! You may not get all of the fibres out of the tracks but you do need to get rid of most of them. If at first you don’t succeed... You may discover at this stage that you have not used quite enough heat and the toner has not stuck well to the board. If this is the case, you can remove the toner with automotive paint thinners and start again with a fresh printout. Make sure you do a really thorough job with the iron. Etching Once the pattern is properly transferred and appears to have adhered properly, you are ready to etch the board. All of the normal aqueous etchants work well with this method but I prefer to use ammonium persulphate, at double normal concentration and very hot, to avoid undercutting thin tracks. Once you are finished etching, the toner can be removed with a cloth moistened in automotive paint thinners such as Prepsol. Then you can drill all the holes and cut the board to size. (Often it’s easier to do the reverse – drill the holes while the toner is still on the board, then strip it and cut it to size. We would also spray the board with a solder-through PCB lacquer to prevent oxidisation.) So there you have it, a cheap, easy way to make PC boards that are nearly as good as photo-etched boards but at a fraction of the cost. Boards produced by this method do have a few limitations though; very thick and very thin tracks sometimes don’t work that well but the results Designing your own PC boards is not too difficult, particularly when you use one of the many software packages around. They also allow you to print your pattern out reversed, ready to use in the process outlined here. This software is PCB Designer 1 – you can download a trial version from the ’net. with most of the boards published are quite good. As with all PC boards, commercial or otherwise, you should always give the pattern a thorough check before building a project. Use the published pattern as a guide or, if this is not available, print out another copy to check by. And one final tip: if you’re printing a pattern off the web, always ensure your board size agrees with the project board size before etching (SILICON CHIP always gives the size of the board in the parts list). We’ve seen whole production runs of double-size boards! The PCB Designer 1 program mentioned above is a 31-day evaluation version and is available from http://shareware.cnet.com/shareware/0-13628-500-2089325.html?tag=st.sa.16165_501_1.lst.titledetail Because it is such a long address we’ve also published it in the “Panels & PCBs – November 2000” page of the SILICON CHIP website (www. silicon-chip.com.au) – all you have to do is cut and paste the address into your browser. Easytrax is freeware and is also available via the ’net – try http:// www. protel.com.au/etech/freeware_ SC home.html Step 5: set the iron to its hottest (‘linen’) with steam turned Step 6: remove the paper fibres by wetting thoroughly then off. Iron firmly on a hard surface until the paper is scorched rubbing gently but firmly. This takes some time but when and the sticky tape starts to bubble. Allow to cool. successfully completed, your PC board is ready to etch. 74  Silicon Chip