Making a PCB
Introduction
It's been a long while since I seriously dabbled in electronics projects. I'd built the odd small circuit on Veroboard but nothing really serious. The last time I actually constructed a serious project, it was my GCSE Technology project.Looking back on it, it was very handy to have the full use of the school's equipment and I was always actively encouraged by the teachers there. Stuff I took for granted with very much possible - use of wood and metalwork tools, PCB etching, bench power supplies and oscilloscopes. Now I have no such facilities to use except for my own, which are limited mainly due to not having a suitable space for a workshop, and being totally skint :)
The main thing I miss, was the use of the school's PCB etch tank. While you can do some very creative things on Veroboard, there are times when only a custom designed PCB will do. Of course, the chemicals to etch PCB's are readily available from suppliers like Maplin and Rapid Electronics, but to be most effective they need to be used correctly.
PCB Artwork
The biggest thing I had trouble with at school was producing decent PCB artwork. In those days, the way I used to do it was to work out the layout on 10mm squared paper, and then trace this onto tracing paper. This could then be turned over to produce the mirrored image that I then had to draw onto the PCB - manually - with a Dalo marker.
Obviously, this is tedious, error prone, and rather inaccurate especially as the Dalo ink tends to puddle, meaning traces aren't sharp. The only other viable alternative at the time was Photosensitive board, where you expose the board to UV light with a mask image of the layout. The problem is, you need a UV lightbox, chemicals for developing which are quite caustic, and the Photo-sensitised PCB is (was) a lot more expensive than the standard stuff.
Fairly recently, I came across a few web pages mentioning the "Laser Toner Transfer" method. The basic idea was that laser "ink" isn't really an ink at all, it's a plastic that is fused to the paper with heat. By printing a PCB layout onto a glossy paper sheet, the toner could be ironed onto the PCB using a hot clothes iron. There is a special material for this sort of job called Press 'n' Peel but it is expensive, something like £20 for 5 sheets of A4! The method I was reading about used standard "Photo Paper" which has a glossy surface as the carrier medium, and can be aquired from pretty much any stationers for reasonable prices.
A link to the article that has the most detail is here
Testing
Having aquired a Brother HL-1040 laser printer, I decided to give this method a go...
The thing that seems to make or break this method, is the structure of the paper. When I tried with some cheap photo paper, all that happened was that the glossy backer came right off with the toner onto the PCB. This then had to be removed manually with a small brush, which was tedious and damaged the traces. It was only when I spotted some Kodak "Ultima" photo paper on special offer at Partners, that I decided to give some better quality paper a try.
It was worth the gamble. The Kodak paper seems to be actual photo paper of the same kind used for 35mm prints, rather than ordinary paper covered with a glossy backer material. The only issues I seemed to have were some larger traces not being transferred fully, and I think this is down to not using even enough pressure when ironing. Glitches like that are pretty easily touched up with an etch resist pen.
Etching
The all important part of course, once you've gotten your design onto the PCB, is to etch it. This involves the use of fairly strong acid's to eat away at the copper. The choices I have read about are:- Ferric Chloride - Old faithful, pretty much what all schools use. It's cheap, but it smells bad and stains anything it touches a horrible brown colour. The fact that it's cheap and easily available is about the only good thing!
- Sodium Persulphate - A little bit more expensive, but very good, clean, and not too dangerous. It also starts out clear so you can see your board etching very easily
- Ammonium Persulphate - Similar to above but a little more hazardrous. I've not seen this for sale in the UK
- Hydrochloric Acid/Hydrogen Peroxide - I have read bout this but it is FAR TOO DANGEROUS to consider using! It gives off hydrogen fumes, can't be stored and burns anything it touches almost instantly. Avoid unless you have a death wish!