Homebrew Tips

Helpful Hints from a Homebrewer...
PC Boards Save yourself some work ... make your boards "surface-mount" whether you use surface mount components or not.

Many of my board layouts use mostly the TOP surface of a double-sided board, without drilling - a lot easier to modify and change without removing the board. Also a lot easier to lay out intuitively, without software - cover with mylar tape and get your X-Acto knife out. Nice big ground plane on the bottom for stability, into which you can cut a few traces for power or whatever. I use a mix of conventional and surface mount parts - depending on values available. Start with your typical .1 uF bypass capacitors, maybe some 5-10 uF tantalum capacitors, and you've already saved a lot of space, even if everything else is conventional.

If you do photo-etch processes from commercial board patterns, just flip the board horizontally in the software to use it on the top plane. (Easy to do with a scanner)

Wouldn't you know it - the homebrew publications have taken to calling this "Pittsburgh style" homebrewing! Perhaps I should lay claim to it as "Milwaukee Style" since I wrote it here first :-) ...

Photo-etching success... After years of various tape and resist-pen methods of laying out PC boards for etching, I'm finally starting various photo etch processes. 

The big stumbling block (for my cheap ways, at least) was the expense of commercial pre-sensitized boards, since I have this nice big stock of board material I got at swap meets. So I'm starting to look for various photo-resist coatings you can apply yourself. You have to look around a bit for these - they aren't in the catalogs of the bigger suppliers.

FIRST SUCCESS: a local store has GC Electronics positive resist sensitizing spray, and the positive developer. Spray it on (in semi-darkness), air-dry for a while, cure overnight in a dark box, and there you are.

I drew my layouts with the drawing tools in Lotus Word Pro 97, which for a generic program work better than the ones in Microsoft Word 97 - nice dotted grid can appear, down to .05 inches. (Mastery of other dedicated software yet to come)

For a transparency, ink-jet printing onto ink-jet window decals (Avery 3276) has worked for me, as well as inkjet transparencies. With my Epson 850, I print at 1440 dpi, flipped horizontally, and I run it through twice (letting the ink dry between passes) for a nice black layer - amazingly good registration if you're careful to adjust the paper feed. Laser printer or copier toner on appropriate transparencies is blacker, but my inkjet method works, too. Inkjet transparencies like this should dry thoroughly so they won't stick to the photoresist on the board.

I put the decal or transparency onto the inside of the glass in a drug-store picture frame - so the ink faces the sensitized board surface you'll be putting in. (Dry the ink overnight, too, to keep the transparency from sticking to the board!) In semi-darkness (yellow bug light in the next room), put the board onto the glass and put the cardboard into the window frame to hold things together reasonably firmly. Expose it to a 15 watt UV black light, about 6-9 inches away,  for 3 minutes. Develop in the GC Electronics positive developer - diluted 4 parts water  to 1 part concentrate - takes about 30 seconds to 1 minute. Rinse the board, touch up any problem areas (gaps, bad spots) with a resist pen or nail polish, cover the ground-plane side with tape or other resist, and etch. 

Results depend on the evenness of the coating you put on, flaws in your board, etc. At its best, it shows up some very fine lettering I put on the board for component identification. Who knows, maybe you can etch dial markings, meter scales, etc., for a unique front-panel look!

Datak ER-71 spray-on NEGATIVE resist and its matching ER-8 negative developer (so you have to invert your dark/clear spaces on your transparency) - available from Electronix Express. Arrived... it's in a pump spray bottle. To coat, you need some hot air - board at about 140 degrees when you spray it, drying at 140 degrees. I got by with a variable heat gun and just estimated by touch! Trouble with this coating is that it's so hard to see, because it's so clean and clear, but it seems less gummy than the GC positive spray. An exposure for  7 minutes to my fluorescent "daylight" 15-watt tube did a good job. The developer seems less acrid than the sodium hydroxide that GC provides, and is pre-mixed. Develop 30-45 seconds in one batch of developer, dry on tissue without wiping, then dip in a second batch of developer for 10 seconds.  As the developer dries, you can finally begin seeing the etching pattern. The resist is soft after developing, so don't touch it or it will smudge/scratch easily. Let it dry for a while, touch up, and etch. 

Injectorall positive resist liquid PC197, and developer D3 - available from Ack Supply and elsewhere. Again, yet to arrive and test...

Connection Pins Some ways to enable fast connect/disconnect for testing...
  • In a conventional drilled board... stick the heaviest wire you can into your PC board connection holes, and then you can lightly solder and unsolder your connection leads
  • Better yet, use some kind of push-on connector for the lead, and a pin soldered into your board. I've used the snap in contacts for Molex connectors, as well as the pins/contacts from DB-style computer connectors. In both cases, trim the pin that you put on the PC board appropriately. Then be on the lookout at your swap meets and surplus houses for the best buy...
 Hot-melt glue - better than duct tape! Handy hot melt can:
  • Bundle wires together
  • Mount wires to chassis
  • Hold down all kinds of stuff
But don't wait for your glue gun to heat up:
  • Careful use of those small butane torches can quickly melt as much glue as you need. Just melt the end of the stick with the flame and let it drip where you need.

e-mail to john at seboldt dot net (note spamfoil format - type in standard e-mail format to reply ;-) )
Milwaukee, WI