I hesitate to stoke the off-topic boiler, but seeing as I started this off with a contentious point please indulge me... > From: Byron A Jeff > > [SJH wrote:] > -Forget wire wrapping! Making a PCB is so easy these days. But first, > -prototype the circuit on a breadboard. > Well this is a religious argument. Each has their advantages and disadvantages: > > Breadbording: Quick to throw together. Easy to change. Entirely too easy to > change. > > Wirewrapping: Quick to throw together presuming you have the equipment. Sockets > cost more than PCB sockets. Too much extension from the bottom of the board. > Fairly stable and generally easy to modify. > > PCB: Please tell me how to make an inexpensive, consistent PCB. While it > may be easy to do, many of us have not set up the design tools and equipment > to put it together. I'll gladly take a lesson in easy PCB making. Yes, consistency is a good point. After much weeping and gnashing of teeth I have found a routine which works for me. I recommend anyone considering making PCBs to spend a whole day working out a good routine then sticking to it. I use precoated positive photo board. Saves worrying about the zillions of variables which can affect the process of making your own (thickness, baking temp, dust, hairs, dust, resist-eating moths, dust etc. etc.) 1. Draw the board on white bond paper. Use a laser printer or use a 0.5mm drafting pen. Print/draw mirror image so that the pattern will be correct when the ink side is pressed against the board. I use Protel but have also used drafting techniques. To draw nice pads, I drilled a DIP pattern into my square so that running the pen around each of the holes results in a nice round pad complete with drill guide hole. (Relieve the underside of the template to prevent ink smears). 2. Sandwich board and pattern between 2 sheets of glass with ink side against the board. Expose to white fluorescent lights (4 x 20W tubes about 200mm from board) for about 1 hour. Yes, this is slow but it gives time for the finer things in life such as preparing the developer and etchant. 3. Develop in commercial developer (or NaOH in a pinch). Etch in hot ammonium persulphate, preferred for its transparency and non-staining which is always an advantage when sharing the kitchen with the boss of the house. Don't leave developer in glassware - I etched a good erlenmeyer flask by not rinsing immediately. Throw away developer after use. 4. Drill then solder. I find that removal of the resist is not required before soldering and in fact forms a nice barrier against my sweaty little fingers. (Be nice if it was actually flux, wouldn't it?) Note on using laser printers: since the paper is not gripped by punched holes etc. don't expect the laser to produce perfectly dimensioned artwork. This is especially a problem when doing long edge connectors or trying to register two patterns for double-sided work. 75mm boards are about the upper limit for my HP laserjet. 15mil traces and clearances are the limit for a 300DPI printer and 10mil for a 600DPI. If you know a little PostScript (TM) then post-processing of the artwork can be quite easy. A favourite of mine is to change the output from Protel so that it a) sets a black page, b) outputs the pattern in white with everything oversize by 30mils and c) outputs the original pattern in black. This gives a pseudo ground plane for SS boards. Optionally, you can connect all the copper islands left by this process using the drafting pen. If cutting the board to size using an angle grinder, leave a 10mm zone around the edge where no copper will be required. The heat of grinding ruins the resist for about 6mm either side of the cut. Fluoro lights should be mounted to give a perfectly even illumination over the board. If the board is tilted slightly to the tube axis or at one end of the tube, you will be surprised how unevenly the resist will develop. If in doubt, move the board to twice the original distance and quadruple the exposure. Heating the etchant is recommended unless you like watching paint dry. I used to heat up ferric chloride in the microwave oven. Since ammonium persulphate is made up as required then discarded, just use boiling water when making it. Don't use at over 80 deg C otherwise the resist can get damaged. Hairline breaks in the traces are a severe annoyance. They can be minimised by ensuring that the printer toner is in good condition, and examining the backlit pattern for breaks. Such breaks are repaired with the drafting pen. Filled-in drill guide holes are another pest. Cured by ensuring the resist is fully developed! Many a good DS board has been damaged by using blunt drills. When the drill breaks through the other side it lifts the pad there. Tungsten carbide drill bits last more than 10 times as long as HSS but must be used in a drill press. They also cost ten times as much. It's a pity, but I've never seen nitride coated HSS in PCB sizes. > > Pre-etched PCBs: Been experimenting with these lately. Shows promise. I'm > talking about the Rat Shack boards that are etched to look like breadboards. > Simply solder in the sockets, components, and wire. > > Each has advantages and disadvantages. Generally while I'm designing and > testing I wire wrap. Easy to put together a semi-permanent board that can > be changed if necessary. I'm willing to examine PCBs but all I read in the > sci.electronics newsgroups is how difficult it is to get good boards.... > Single sided with min. 20mil traces is easy. Double sided and/or 12mil is a pain. However, by dint of much practise my boards are turning out so well that I wouldn't consider wire wrapping or solder tags (remember them in the days when components were big enough to see?). Total investment: { PC; EasyTrax; Laser } or { Staedtler/Rotring drafting pen }; 2 glass sheets; fluoro lights; Plastic tray(s); PCB drill. Consumables: precoated board; developer or caustic soda; etchant; drill bits. Regards, SJH Canberra, Australia