So last time I mentioned I had grabbed a beginner’s etch set – the A200 by a German company Kemo Electronics – from JayCar with ambitious plans to make a breakout board for this surface mounted CMOS camera sensor I wanted to play with. In retrospect, I could have purchased most of the items in the kit individually and I would have probably gotten better value for money that way, but I guess where this kit shines is that it allows beginners to inexpensively experiment with two methods of PCB development by including most of what you need in one package. Now one of these methods – involving the use of a photoresist coated board – required the use of UV lighting and a photo-positive template printed on transparent media, which I thought was a bit too sophisticated for my first attempt so I opted for the simpler toner transfer method.
Now my inkjet printer wasn’t quite going to do the trick here, so I grabbed a used HL-2140 Brother laser printer off Trade Me for $25 (great deal). The OEM replacement toner cartridges for these printers tend to be overpriced, hence why people probably just prefer to sell them and buy a new one at a fraction of the price it would cost to restock the old one. The trick is to find a used printer for which third-party compatible replacement toners are available since these tend to be much cheaper. I got one for $18 off Trade Me, which is about 1/5 of the price of an OEM one.
Next I needed a print media which would facilitate the toner transfer process. My research online seemed to point to glossy photo paper as being best, however the 20 sheet pack of Brother BP61GLA A4 paper I tried was an endless source of frustration. Ironing this paper with the PCB prints unto the copper clad board would not only transfer the toner, but also glossy substrate which seemed to have plastic consistency. This left an etch resistant semitransparent plastic film over the board which had to be delicately scrubbed off, taking care not to ruin the desired transferred toner pattern. After repeated making a mess of this, I followed some other advice online and used magazine pages instead, which are a bit thinner so if your printer has a “paper thickness” setting like mine, set it to “thin paper” to save yourself a lot of stress with paper jams. Magazine pages are wax based and this means that they won’t bond strongly to the toner, and with a little heat from the iron, readily transfer the patterns to the copper clad boards. They also required a lot less soaking in warm water to cleanly separate from the board than the glossy photo paper. The only caveat was that I just had to be careful not to apply too much pressure with the iron while transferring the pattern, since this caused the molten toner to bleed laterally and in some cases form bridges between traces. I then used a permanent market to touch-up any imperfections in the transferred circuit. One important lesson I learnt was how important it was to properly clean copper surface of the board in preparation for toner transfer otherwise any contaminants (e.g. I’m guessing fatty acids from hands) would cause the transferred toner not to bound with copper board in some spots. I found isopropyl alcohol on a paper towel (not dish washing detergent as some suggested) works best for this.
Contrary to the instructions from the kit, I did not dissolve the entire 100g sachet of sodium persulphate (the etchant) into 1/2 a liter of water but rather I only used 1/4 of the sachet (weighed to 25g) with 1/2 a cup of warm water since I only planned on etching very small board. This stuff is toxic and requires special disposal so it’s best to just keep it in a container reuse for as long as possible by adding addition etchant when necessary. I just needed a hot water bath to raise the temperature of the solution for subsequent reuses. My board etched within 1 hour and from there it was just a matter of washing it clean with water, drying it, and removing the toner with acetone (nail polish remover) to reveal the copper traces.
