Homebrew PCBs

This evening i put the first toner transfer board i made in the etchant, it 
worked like expected.

The tracks are a bit rougher than with optical process, and i have some 
closed drill holes (not used toothbrush only thumb).

I hope i can get even better results with the new toner (still not here) 
because the coat is very
uneven.



The first board was assembled very fast, so i decided to make also a second 
one.

The printing and transfer was without much trouble.


For etching i used a very small plastic container, only filled where the 
boards
are with maybe 5mm etchant.
The first worked very well, i put very few drops H2O2 in to get things 
started (the etchant was reused from previous
boards). The 35u board seemed to take long as i have mostly used 18u in the 
past.
But it got ready in normal time, i put it out and put the etchant away (but 
left it in the small container
and didn't put it back in the bottle.)

Now, a few hours later i put the second board in the same container with 
still the same etchant.
The first minutes all was well, i added again some drops h2o2 because it 
looked like it has vanished in the meantime.

(If i put a board in etchant without fresh H2O2 the pcb surface gets dull 
brown/red.
if i add H2O2 it instantly gets bright shiny copper colored (almost 
yellowish brass colored.

The etchant turns from blue/green a bit more to green if i add H2O2.


But to the problem:
After some minutes on a spot on the board some blue sludge formed.
After a while it had covered the whole board!
I put it out and cleaned it of (it was maybe 1mm blue sludge, soft).
But as i put it in again nothing happens.
The board only gets dull red/brown like if no H2O2 is in!


So, i thought i know that, this needs H2O2....
a few drops more in there.....


It began to sizzle slightly again, BUT it didn't get shiny copper colord 
like i wanted!
it did only form green sludge again!

Next thing i tried:
Add a few of the etchant storage bottle.
Result: green sludge dissolved partially, but still not etching much.


Next experiment: Add HCl
Result: etchant turnns from Blue to green again (like i know and like it)
But still not much of etching action here.


As a last try i put again some H2O2 in.
it worked, and completed the etching.




But i really would like to know what was going on there?
Why did it need H2O2 again after adding the HCl?
What happened to the H2O2 from before?


What was the green sludge? Cu2Cl2?

Is it dissolved by HCl?





If i make the etching tank, permanently containing a relatively big amout 
of etchant, how much H2O2 do i have to add each time? Depends this amount 
of the copper to be removed or the liquid
volume?

I very appreciate the thought of having a permanently ready etching tank, 
especially now as the toner
transfer works...
But if that means i have to use some 50x more H2O2 EACH time etching i 
don't like the thought any more.
I think the additional HCl is determined by amount of copper etched, it 
only is for providing Cl
for the Cl2CU2 to get Cl2Cu again?

But the H2O2, i still don't understand fully what it does.
I know it adds oxygen, to form water? from the H of H+Cl?

But why then do i need it to get the slightly sizzling bubbling action 
going?
I mean if it is only for "regeneration" it should still work hours after it 
had
worked when i put the last board out?



You see i'm pretty confused now...
But the board finally is ready and i can heat up the soldering iron...


I would really like to understand this finally, especially if it makes 
sense to have a big etch tank
ready. (max. pcb size at least 100x160mm, but most time i make only 
50mmx50mm pcbs...)
If this will require huge amounts of H2O2.


And i have another question: the gas, forming if it has too much H2O2 (very 
light bubbling is all the time).
But if it is too much you can smell the gas, i assume it is Cl gas?
It may too be oxygen but it smells not like it (how smells oxygen? ;-) )
I try to avoid too much H2O2, i think Cl is not healthy.... Why does it 
form?

thanks for any help...

st