Homebrew PCBs

hi Grant,

I'm just letting you know that I'm doing another test reacting 
copper and HCl. Its been about 30 hours now and the copper mass 
is already 60% of original mass. The 1st 23 hours was just left 
stagnant in open air, and the solution went a fairly dark color 
over that time (you could still see through about 2 centimeters 
of it). After 23 hrs I added more acid (HCl @ 5.5Molar) and 
bubbled air. I'll post the results when all the copper has dissolved.

I cannot say what is happening with your solution. If the liquid 
is still relatively clear after all these days then there must be 
something terribly wrong.

Grant, I took a 500 ml beaker. Added 20 ml of 8M HCl (20% 
wt) + 20 ml of water and pieces of scrap copper sheet 0.7 mm
thickness. At this stage about 1/2 of the copper was
above the liquid level. Over a 54 hour period I measured the 
progress.


   time    HCl     Cu mass   appearance
(hours) (Molar)   (grams)   of solution
---------------------------------------------
    0      4M       12.3g     clear
   12      ?        ?         pale brown
   23      ?        10.0      Coca-Cola brown
-> added 20 ml of 8M HCl + 5 ml water.
-> started bubbling air through solution.

   23      5.45     10.0      "       "
   34      3.77      3.8      dirty brown liquid
   46      2.4       0.7      dirty brown liquid
   54      1.67      0.0      deep green


Note: The bubbles were created from a air hose immersed in 
the solution. If an airstone had been used to create smaller 
bubbles then the reaction would of been much faster.

regards,

Adam.

Hi Adam -

My etchant continues to slowly progress. It seems that some variable
at this end differs from your approach. Nevertheless, the solution has
slowly changed in the same ways you described.

At present it is a dark coca cola brown, and it is difficult to see
much of the wire under the etchant, although maybe the top inch of
solution is somewhat translucent. Overall, the solution has become
darker and less translucent over time.

I had recently placed a piece of PCB in the solution. It took about 2
days, but all the copper is now gone - so clearly, the etchant is etching.

My tire air compressor failed. It is not meant for continuous duty,
and the conecting rod to the compressor cylinder was what actually
failed, no doubt due to overheat. The compressor directions warned not
to run it over 15 minutes without a 5 minute off period. Since the
pressure was quite low, I hoped that the work done was slight enough
that continuous duty might be ok. Obviously not. The other drawback
with this device was noise. It was extremely noisy.  I could hear it
from the basement through two closed doors, and this would have made
it impractical. It did put out lots of air, though.

I finaly got an old Gast vacuum pump going as an air source. I had to
do some work on the motor before it worked. The pump itself has carbon
vanes and they are probably worn, but I suspect that replacement would
be too expensive even if I could find replacements. Meanwhile it has
some bubbles rising through the etchant.

I am hoping that although the process is slow, it will succeed in the
end. I will keep the list posted.

Grant

--- In Homebrew_PCBs@yahoogroups.com, adam Seychell
<adam_seychell@y...> wrote:

> Grant, I took a 500 ml beaker. Added 20 ml of 8M HCl (20% 
> wt) + 20 ml of water and pieces of scrap copper sheet 0.7 mm
> thickness. At this stage about 1/2 of the copper was
> above the liquid level. Over a 54 hour period I measured the 
> progress.
> 
> 
>    time    HCl     Cu mass   appearance
> (hours) (Molar)   (grams)   of solution
> ---------------------------------------------
>     0      4M       12.3g     clear
>    12      ?        ?         pale brown
>    23      ?        10.0      Coca-Cola brown
> -> added 20 ml of 8M HCl + 5 ml water.
> -> started bubbling air through solution.
> 
>    23      5.45     10.0      "       "
>    34      3.77      3.8      dirty brown liquid
>    46      2.4       0.7      dirty brown liquid
>    54      1.67      0.0      deep green
> 
> 
> Note: The bubbles were created from a air hose immersed in 
> the solution. If an airstone had been used to create smaller 
> bubbles then the reaction would of been much faster.
> 
> regards,
> 
> Adam.

grantfair2001 wrote:
> Hi Adam -
> 
> My etchant continues to slowly progress. It seems that some variable
> at this end differs from your approach. Nevertheless, the solution has
> slowly changed in the same ways you described.

Good point. I'm certain there is probably some very 
important variable(s) that I do not know of yet, and maybe I 
just happen to fluked upon it. I suspect air/copper/liquid 
interface has an important part in the initial reaction.
Maybe the copper should be positioned above the acid, and 
the sparger turned on so it continuously wets the copper 
with fine droplets. That way the lid can remain on.

I know that the reaction accelerates as more CuCl2 is 
produced. Once the solution goes dark brown and copper is 
well on its way to etching, then the limiting factor becomes 
the amount of air that the solution can absorb to continue 
the reaction of copper(I) to copper(II).  As I said earlier 
the copper(I) is the main etchant inhibitor.



> 
> At present it is a dark coca cola brown, and it is difficult to see
> much of the wire under the etchant, although maybe the top inch of
> solution is somewhat translucent. Overall, the solution has become
> darker and less translucent over time.
> 
> I had recently placed a piece of PCB in the solution. It took about 2
> days, but all the copper is now gone - so clearly, the etchant is etching.
> 

yep, its etching. But don't let 2 days worry you. If there 
white film of the copper when you pull copper out of 
solution then its saturated with copper(I).

> My tire air compressor failed. 

These machines are *not* designed for continuous use, and 
I'm not surprised it keeled over. I use a largish aquarium 
pump, which are designed for continuous use (and quiet). 
I've just been searching for a larger air pump, and found 
that they are used in hydroponics, along with all the 
necessary airstones accessories for creating lots of fine 
bubbles. DIY hydroponics seems quite popular in Australia, 
enough to have a dozen or so shops to choose from in my city.

> 
> I am hoping that although the process is slow, it will succeed in the
> end. I will keep the list posted.

I know this process of mine to make CuCl2 etchant is far 
from optimum so I'll keep chipping away at the problem. I'm 
certain its possible to be made without a drama , but just 
need to do a bit more learning to get there.

Thanks for keeping us updated.

Adam