Homebrew PCBs

> Wow really small quantity !!! last question, Can it be regenarate for
> ever , or should be dispose after some H2O2 addition ???
>
> Thanks
>
> Bruno

You can use it indefinitely. Of course HCl is also used up, so you need to  
add that too after a while. You can either go by feel and add when it  
doesn't help to add H2O2, or you see any blue sludge on the PCB, or you  
can look in the links section on how to measure the molarity of HCl in the  
etchant. Look for the method with the two eyedroppers it is the only one  
sufficiently simple IMO. You might also want to get a hydrometer. It is  
used to measure density (amount of copper per volume). You can get one  
cheap and easy in the car tools store, it is used to measure battery  
fluid. Should cost well under 10$. Go for the type with the swimming  
hydrometer in a large glass pipette, not the small plastic rotating  
pointer one. But that's really only if you are curious about the etchant,  
it is not a requirement to make it work.

Now if we only keep to add stuff to the etchant it will of course grow in  
volume. This is very slow and is good because it dilutes the copper in  
more etchant, otherwise you will reach a point where the specific gravity  
gets too high. Should you get too much etchant at one point you'll have to  
dispose of some, but unless you make really many boards regularly the  
growth is barely noticeable.


You will find if you keep using your etchant it will gradually turn from  
HCl+H2O2 etching to CuCl etching, that means instead of "instantly" using  
and needing H2O2 to etch the H2O2 can be used to regenerate existing CuCl  
in the etchant. What that means for you is that once there is enough CuCl  
you do not necessarily need to add H2O2 each time. You only add it when  
the etchant turns from a bright green to a darker, brownish  color. If  
there is enough bright green regenerated etchant for the board there you  
do not need to add any H2O2, even if you last etched months ago. OTOH it  
will not help to add too much H2O2 - once all the etchant is bright green  
it does no good and will just decompose to useless oxygen that has nothing  
to regenerate and is released into the air.


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> If it fizzes, you added too much. It won't actually do any harm if youdo  
> put too much in. I normally fill the cap of the bottle up and tipthat  
> in. It seems to be about right for my tank.
> Les

if it fizzes it creates loads of nasty fumes that are corrosive. It's  
definitely too much if it does that.

ST