Homebrew PCBs

On Mon, 26 Mar 2007 17:13:25 +0200, mycroft2152 <mycroft2152y@...>  
wrote:

>
> The acid etching process does generate heat and bubbles. There can be
> a mist of etchant that is almost invisible. You will notice the
> effects, if not immediately, but in a very short period of time. Acid
> burns cause intense pain and heal very slowly. Fabric distegrates.


Those are generally symptoms of too much acid or H2O2 or both. It is a bit  
tricky, maybe impossible, to avoid bubbles completely when working with  
fresh HCl H2O2 etchants, but an excessive amount should be avoided. I have  
once timed a board at eleven seconds, so i know what it means to use too  
much (it was a tiny board and tiny container), do NOT try this with large  
amounts. Anyway, reducing concentrations should reduce bubbling, and stop  
the etchant heating too much (which will generate lotsa HCl fumes too). Of  
course it'll slow things down and you might even have to replace or  
replenish the etchant during the etch if you work with small amounts in a  
small container, on a freshly made per board basis.

If you can at all get H2O2 in concentrated form, or if you are prepared to  
go through the trouble of regeneration with air oxygen, it really pays to  
feed it up to a proper CuCl etchant. I have my etcher (with a lid, but not  
at all airtight), right next to the corner where i store round stock and  
rods and stuff, some of it steel, and notice no corrosion. The etchant  
does not produce any smell or fumes or bubbles, only during etching a  
slight smell can be noticed from the air pumped through (agitation). Also,  
CuCl only contains HCl in a relatively low concentration, so will not  
cause burns (at least if washed off soon). It will only need tending with  
additional HCl and H2O2 every few boards (depends on total volume) so the  
risk can be reduced and proper gear can be worn at those times.

Having used both, permanent CuCl is much more comfortable, but you need  
concentrated H2O2. Maybe electroplating regeneration would be an option  
for those who can't get H2O2 easily. Maybe O2 gas in bottles (welding)  
would work better than air, possibly using something like a downstream  
dissolver, possibly an option if someone already keeps a oxy/acetylene  
welder. Maybe it would even be reasonable to generate the oxygen by  
electrolysis of water, but then it is probably easier to use  
electroplating and feed the generated gas into a dissolver.

ST