Homebrew PCBs

Okay, starting to make some sense.  But, finding and buying 
chemicals isn't the easiest thing to do these days.

So, a couple of follow up questions.....


hydrogen peroxide (H2O2), is this the same as what I can purchase at 
the local drug store? Or, is there a stronger solution or something 
I have to get at a specialty supplier?


hydrochloric acid (HCl), I know I have seen this for some purposes 
but can't recall common uses - toilet bowl cleaner perhaps?  Again, 
where would I purchase this, and is there a certain strength I 
should look for?


With this chemical make up, do you still want to use a heater?

Does anyone know which plastics will be okay to use as a tank for 
this type of etching? I was thinking of using Acrylics, but that 
stuff can be a pain in the ass to glue up good.  Then I thought 
about polystyrene which you can get translucent and I believe it can 
be glued up more readily.

TIA, I am getting closer to understanding it :-)

Chris














--- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan" 
<stefan_trethan@g...> wrote:
> On Sat, 20 Aug 2005 02:38:22 +0200, <JanRwl@A...> wrote:
> 
> > Can someone here PLEASE outline the procedure and chemistry to  
use for  
> > this
> > etch-method?  I have never seen ANYWHERE a list like,
> > "1.  Boil the bare blank in swamp-water;
> >   2.  Incant;
> >   3.  Swish the board around in a 30% CuCl solution  over 80°C 
for 15  
> > minutes;
> >   4,  Etc. etc."
> > With FeCl, you can omit steps 2. and 4., and the result is  
fine, but  
> > messy.
> > Please?
> 
> 
> I'll try.
> Let's divide that into 3 parts:
> Etching boards, maintainance, and first "brewing" of CuCl.
> 
> 
> For normal etching, you'd need to do nothing much. You'd just put 
a board  
> in, and add H2O2 if the etchant is too dark in color. a few ml is 
enough  
> to oxidize it. The color is all you need to determine if it is ok 
or needs  
> something. Then you turn on the bubbler and simply wait until 
done.  
> Nothing needs to be done after etching.
> 
> The adding of hydrogen peroxide (H2O2) takes the hydrogen away 
from some  
> of the hydrochloric acid (HCl). That means the chlorine is freed 
and can  
> "take" one copper from Cu2Cl (the dark brown stuff) to form more 
CuCl  
> (light green), and water. CuCl is now prepared to take a second 
copper  
> again, thus etch the board. You can also introduce the oxygen from 
other  
> sources, like pumping air through it (takes long), or even 
chlorine gas  
> directly, but that's poisonous.
> 
> 
> maintainance:
>  From time to time you might want to measure the molarity of the 
HCl in  
> there. That is, how many hydrochloric acid is still "free" (not 
carrying  
> copper) and can be used to form CuCl. Because every time you add 
H2O2 some  
> of the HCl is converted into CuCl. At some point, if all HCl is 
used up,  
> adding H2O2 will not bring on the expected brigtening of the 
etchant and  
> increase in etch speed. Also, the etchant will have a bluish color 
ad  
> deposit a blue sludge on boards. This is a sure indicator there is 
not  
> enough HCl, but you sould have added some by then.
> 
> To measure the HCl molarity, you need 4 things. A alkaline 
solution of  
> known molarity (NaOH), some indicator (like methylorange), and 
two  
> eyedroppers. You can get your NaOH solution by solving a weighed 
amount of  
> developer in water. It should be a 1 molar solution. How much you 
need to  
> weigh is said in one of the pages in the links section. When you 
have that  
> the procedure is simple. Put 10 drops of etchant in a small 
container, add  
> some water if you like, and one drop of indicator. It's now 
orange. Then  
> add the alkaline solution drop by drop, all the time swishing the  
> container to mix it. When it turns green stop and your number of 
alkaline  
> solution drops added is your molarity after dividing by 10.
> I don't do that often, and usually only add HCl by feel. A wide 
range of  
> molarity will be ok. I keep it around 1. Still every few months i 
feel  
> like checking the molarity.
> 
> There's also the density to be measured. Adding the copper makes 
the  
> etchant more "heavy". In a away this is good - because you'll have 
more  
> CuCl do do the etching. But if it gets too much you need to remove 
some  
> etchant and add water. I have never encountered this, i guess the 
water in  
> the HCl and H2O2 added is enough. You can measure the density with 
a  
> hydrometer, which you can simply by in a car parts store, as a 
tool for  
> checking car battery acid. It comes in a neat huge "eyedropper" in 
which  
> the hydrometer swims.
> 
> 
> First brewing:
> Some tutorials call for adding copper in some form.
> I have found you can start just as well with only HCl and H2O2, 
and water.
> At first, you don't have any CuCl, but those two chemicals will 
etch all  
> by themself. You can make etchant up by diluting HCl to about 10% 
and  
> adding a swig of H2O2. Then put in the board and go by color.
> At first there is none or little CuCl, so you have to add some 
H2O2 each  
> time you etch. As copper content increases you get more and more 
CuCl,  
> which does the etching and must only be re-oxidized from time to 
time. I'm  
> now at a stage where i need to add H2O2 maybe each third or fourth 
board.
> 
> Here you go.
> 
> ST