01-04-2017, 04:32 PM
DON'T TRY THIS AT HOME, FOLKS!
I first dabbled with PCB production while I was still at school. I hadn't come up with the nail varnish resist idea at this time and I hadn't a clue where to obtain etching materials but I had another idea. A boy in my class was seriously into chemistry and had struck up a rapport with the pharmacist down the road who would let him have things us other oiks wouldn't be let near - so I asked him if he could get me some concentrated nitric acid!
When I explained why I wanted it, he agreed so, one Friday night after school, I waited outside while he got the acid which he presented to me in a small brown bottle sealed with a cork! With his instructions to keep the bottle upright at all costs ringing in my ears, I set off for home.
Ten minutes walk to the underground and down the stairs. Two stops then change. Up the stairs, down the stairs and wait for the train home. I managed to jam myself into the corner seat for support for the 35 minute journey, then it was off down the High Street and home - about a 12 minute walk. Once indoors I walked right through the house and out of the back door before setting my bottle down on the window sill.
I then decided to remove the cork from the bottle and found to my horror that it wasn't in the bottle but rather resting on top of the bottle with a thin sliver of burnt cork protruding into the neck! I carefully placed the bottle somewhere where it couldn't be stumbled upon by anyone, man or beast, and went inside for my tea.
The next day was Saturday and time for the great experiment. I'd already prepared the board using the graph paper technique to mark the pad positions then drawn the track layout on the polished copper using a black fibre tipped pen only recently introduced by Platignum at a cost of 2/6.
I'd melted some candle wax with which I'd then succeeded in coating the board in a thin layer. Being translucent, I could still see the track drawing through it. Now out came the school compass and, using its point, I'd laboriously scratched a groove all round each section of track, making certain I could see the copper in the bottom of the groove.
I placed the board on the concrete coal bunker, which was conveniently slightly slanted and retrieved the acid. I has a glass applicator from an old bottle of drops which was ideal for getting the acid out of the bottle, being careful - of course - not to squeeze the bulb too hard before sucking!
I dripped the acid into all of the grooves, take advantage of the gradient to distribute it evenly and continued until all reaction stopped. I then washed the board thoroughly and melted off the wax. A quick once over with metal polish to remove the ink pattern and there it was: my very first PCB! All that was left was to drill it and mount the components but now, almost 60 years later, I haven't a clue what it was I was building!
