Re: gEDA-user: experiences using geda with students

[Karel Kulhavy <clock@xxxxxxxxxxxxx>]

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
> 
> 
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