OWN DESIGNS:

I have not yet tried the "PCB software/printout to Deskjet onto acetate" technique, nor scanning in from other artwork. I simply use rub-down transfers onto plain acetates, then sellotape a clear acetate on top to prevent damage to the artwork.

EXPOSING THE BOARD: Place the artwork onto the glass plate of the UV exposure box, (making sure it's the right side down!) and place the lacquered board on top. Close the lid to tightly clamp the board down. If it's not clamped tightly, UV will creep behind the thinner tracks and over expose them.

EXPOSURE TIME: Using the Maplin lacquer with one good coat in a four X 8 watt tube box, I find that an exposure time of four to 5 mins gives consistently good results. (The exposure time doesn't seem too critical). Once exposed, do not expect to see anthing but the feintest sign of a pattern on the board. The pattern will not emerge till developed.

DEVELOPING: I have had no success using caustic soda (sodium hydroxide). I've found that either all or none of the lacquer dissolves. I'm told that you only need a weak solution, just enough for it to feel "soapy" between finger and thumb. Well it won't work for me! I use Maplin's Photoresist Developer, Code: YM62S at £3.79 a 250 ml bottle which dilutes four to one with water. I make about two PCB's a week on average and this developer lasts for at least a year.

I pour it into a "Tupperware" food container, about 10" by 6" so that the developer is shallow and you can see the board developing. (The developer soon goes deep blue) As soon as the lacquer has dissolved and your pattern is fully visible, take the board out and rinse it.

If you find for some reason that the result is unsuccessful, all is not lost. You can clean off all the lacquer, go back to square one and recoat the board! In any event carefully inspect the board for any blemishes such as bridges between track, often caused by a build up of lacquer around dust specks, or holes in tracks due to over exposure. These can be repaired with rub down transfers. Meths on a cotton bud will remove any underexposed lacquer/dust specks.

In the final part, I'll cover etching drilling and tinning.

(All information given in good faith, without liability! I have no connection with Maplin's or any other supplier).

PCB TECHNIQUES, FINAL PART.

In the first two parts I covered equipment, materials and techniques for the UV method. Now a few final comments, firstly on double sided board production and generally finishing off your boards:

DOUBLE SIDED PCBS: There are two situations encountered, firstly when you simply need a groundplane on the reverse side as in RF circuits. All you need to do is to protect the reverse side of the board with sticky back plastic such as Fablon during etching of the other side.

Secondly, when you need tracks on both sides. In this case, place the artwork for both sides accurately on top of each other and drill through them and the board at three register points, such as mounting holes. This will help you to position the artwork at the exposure stage and ensure that when the board is completed the tracks on both sides will accurately overlay one another. Spray, develope and etch one side, protecting the second side with Fablon during etching the first side. Then repeat the process for the second side, protecting the first with Fablon during etching. Do not, incidentally, be tempted to drill any other holes until both sides are etched as the ferric chloride will creap through the holes and start to etch away at the edges of any holes!

TINNING AND DRILLING:

Once etched and cleaned, tin my boards as follows: Smear the copper with a thin coating of plumbers flux. The white stuff used for lead free solder works very well, obtained from DIY stores. Using a wide tip to your iron, put a small blob of solder onto the tip and quickly pass it over the fluxed board in a "brushing" motion. This quickly tins the whole board with a thin even coating and avoids overheating any thin tracks and pads.

Rinse the board and for I.C's, resistors, caps and diodes, drill with a 0.8mm HSS drill (Maplin's code: QY64U, 82p ea.). The Tungsten Carbide drill bits are superior but don't last too much longer and cost £3.00 each. I re-sharpen the HSS ones on a small modelling grindstone ( Mapin's code KW16S, £3.99 for three), held in a PCB drill. For Preset pots, trimmer caps and pcb pins I use a 1mm Maplin's code: QY65V or 1.2mm code QY90X, both 75p each.

SAFETY PRECAUTIONS: Commonsense dictates that all chemicals should be kept well away from chidren, pets and the XYL and containers clearly marked so they don't get used for storing the porrage or feeding the cat! Rubber gloves and eye protection are sensible and don't switch on the UV box without the lid closed!

In conclusion, yes, it's messy, and the cost of the UV box is quite high but once you've geared up, the intitial outlay is soon recovered and you can achieve professional results quickly and at negligible cost. I've made boards for such things as the P.W. Robin Frequency Counter (excellent), the G3TSO TX/RX, a masthead preamp, Baycom/JVFAX interfaces, PSU's, etc etc. Presently I'm making the P.W Droitwich locked frequency standard, which has become something of a nightmare because there were errors in the article and despite an apology and assurance from the Editor in March 96 PW, and two letters from me which have so far been ignored, the errors remain uncorrected, except what I've worked out for myself. However, 'twas ever thus with all radio mags and we soldier (and solder!) on! :-)

Disclaimer: As I've said before, all info and advice given in good faith with no acceptance of liability. I have no connection with any company such as Maplin. I'm just a retired old buffer having fun while my wife is at keep fit and can't see what I'm up to! ( She has, however, long since discovered that Ferric chloride makes holes in shirts and sink unit tops and I've discovered that such mishaps induce earache in the culprit!)

I'll be happy to answer any queries but I don't take orders for boards!!