On Tue, Oct 31, 2006 at 12:15:48PM -0600, John Griessen wrote: > > > Peter Clifton wrote: > > >We run a robot design project, > . > . > . > the desire is (from the project's leader) that the students use gschem > >or similar to draw their schematics. We aren't yet at the stage where > >these students build custom PCBs, however various ideas for rapid > >prototyping (miniature milling setups) have been discussed as a future > >possibility. > > > I saw at one Univ. site, (maybe MIT) a lab procedure about using their > owned spray etching station. I have tested a very environmentally friendly > etchant using HCl and H2O2 and pure copper metal to start off a solution > and it works well enough without spray, and precipitates copper hydroxide > when pH neutralized leaving slightly salty water that can go down the > drain. The copper hydroxide can be sent to the landfill or sold scrap > even. This etchant recipe, originally published by Leo Van Loon, is easy > to see through, easy to replenish by color change, and low risk of eating > holes in clothes, and makes no stains on hands or clothes. Baking soda in > water is all you need to neutralize/rinse just etched boards, and lye, > (NaOH), and pH paper or meter is all you need to neutralize excess etchant. > Replenishing is by adding HCl 35% and H202 35% -- it increases the volume > of etchant, so you drain out some before replenishing the etchant. The > chemicals are available and cheap -- $6/gal for acid, $13/liter for H2O2 > 35%, and those sizes are the right proportions to buy in to make the recipe. > > Here's a board etched with it: > http://shop.cottagematic.com/elab/etched-board-epson-photo-paper.jpg > This photo was out of focus, but it's easy to see in a bubble tank when > laminate substrate is showing -- copper can still be seen on the bottom > edge. http://shop.cottagematic.com/elab/etch-done.jpg
What are the black stains? Places where the patterns were accidentally etched through? Or some kind of corrosion? Is it a picture taken during the etching process or after? CL< > > With spray, it would be a more even etch over panels of boards, and easier > to see the progress of the etch for first time success. When you make some > standardizing assumptions like your board sizes are 90% 2x4 cm, 5% 3x6 cm, > and none are longer than 6 inches; 95% of boards are single sided copper > plus wire jumpers, surface mount only; the etch station is small and easy. > > The main thing to buy is an acid proof pump for the etch spray. If you > have a fume hood to put it in, any old clear plastic or glass can be used > for the low requirements of the tank size and strength, and assembled with > silicone RTV like a fish tank. If you didn't have a fume hood, some kind of > box with a slight vacuum fan to pull air through some baking soda would > neutralize any HCl mist or vapor as it is done and purify the air inside > the etch tank after the spray pump stops. the final thing required is a > fish tank heater. That attaches to the lid so you can make a glass tube to > lid wall seal with silicone RTV (again). > > I have all the parts and will be trying it out soon and report more on this > list about it, and would negotiate to make you a system if there is no one > who can budget time on it at your place -- It would be about $400 for a new > pump, $100 for a used one and about 6 hours or less work to hire to get one > assembled. > > John Griessen > > > _______________________________________________ > geda-user mailing list > [email protected] > http://www.seul.org/cgi-bin/mailman/listinfo/geda-user _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
