Homebrew_PCBs

Wow, you have been hard at work. Congratulations on your findings.

I just bought a new Grade B burette on the weekend and it shipped
today <g>. (I had decided to put off procrastinating . . .)

So - to start out, if I get this right, I can prepare a solution of
0.1 to 0.5 Moles/liter (0.4% to 1.6% w/v HCl) and start etching?

Grant

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

> I found that higher copper gives faster etch. Currently I get
> around 15 minutes etch time at 20°C for 35 um copper, bubble
> agitation with a solution composed of 160 grams/liter copper and
> about 0.2 moles/liter of HCl acid, the specific gravity at 20°C
> is 1.280.

I found that higher copper gives faster etch. Currently I get
around 15 minutes etch time at 20°C for 35 um copper, bubble
agitation with a solution composed of 160 grams/liter copper and
about 0.2 moles/liter of HCl acid, the specific gravity at 20°C
is 1.280.

I've found three variations of cupric chloride operating
parameters online.

#1 http://users.rcn.com/rexa/Projects/CuCl_ech.html and
#2 http://www.pcbfab.com/iepart3.html
#3 http://www.oxfordvue.com/TechInfo/how_does_it_work.html

#1 #2 #3
Copper 75 180 230 grams/liter
HCl 1.0 0.2 0.04 moles/liter
S.G 1.17 1.18? 1.4 g/cm^3
temp. 21 49 49 °C


I'm think that #1 does not have enough copper. The acid seems to
have little effect on the etch rate. It only needs a bit on there
to keep the copper dissolved and to convert the copper(I) to
copper(II) with dissolved oxygen. Interestingly it even etches ok
with zero free acid in solution. All that happens is you see some
insoluble powder float around on the surface, which is blue
copper(II) hydroxide. In fact some commercial PCB etchers run
cupric chloride tanks around the zero acid level. This is suppose
to help the "etch factor".

One thing I found very important is the copper(I) chloride causes
the solution to go dark brown and it will have huge effect on
slowing down etch rate if it gets too high. You can actually see
copper (I) chloride as a white film on the copper and my theory
is this film makes it physically difficult for fresh copper(II)
chloride to react with the copper metal.

So how do you stop copper(I) chloride build up ?

The copper(I) chloride will go to copper(II) chloride with HCl
and dissolved oxygen. The time it takes to remove most of the
copper(I) can be over 4 hours of bubbling. So we can't expect
this reaction to take place at the same speed as our copper
reaction on the PCB. The way around the problem is to start off
with a solution not containing any copper(I) chloride and rely on
its bulk as a buffer for holding freshly generated copper(I).
With sufficient solution volume then copper(I) build up shouldn't
became an issue during etching. After etching, continue the air
sparging until all (or nearly all) the copper(I) is removed. I
don't think its necessary to remove every last trace of copper(I)
so that you see the solution turn clear green, its takes about
two days of bubbling to get to that level.

An excellent test to see if you have removed enough copper(I)
chloride is to take a test tube filled with few cm^3 of water and
add a few drop etchant, so its diluted ( approx. 5~10%). If any
copper(I) chloride is present it will precipitate out and show up
as a cloudy mixture. The more copper(I) the more cloudy.

I know that the etchant can still look an almost opaque dark
green, indicating there is still some copper(I) chloride in
solution, but the concentration must be very small because it
will not show any signs of visible precipitation when doing the
water dilution test. So, if you see a clear pale green or pale
blue when you do the dilution test then you can be assured that
your etchant is ready to rock and roll again.

Since it appears the free HCl is not important then you probably
could survive with just a few graduated pipettes for a quick and
dirty acid-base titration (no expensive burette). The HCl is
needed in order for the removal of copper(I) chloride during the
air sparging. As a guess I'd say you shoudl aim for a HCl
concentration anywhere from 0.1 to 0.5 Moles/liter (0.4% to 1.6%
w/v HCl).

A good quality hydrometer however will be essential for measuring
the copper content.

Adam

grantfair2001 wrote:

> Hi Adam- the HCl I have is 20 deg. Baume or about 31.5% HCl, how
> should I modify your recipe (in message 1367 - Preparation of cupric
> chloride etchant)?
>
> Grant
>
>
>
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>

The price for my Grade B, teflon stopcock 50 mL burette was $48.00
Canadian, which equals AUD$55. I was thinking about buying a used
burette from an internet lab equipment auction, but it was cheaper to
get a new Canadian version. Apparently glass stopcocks on old
equipment can cause problems, and the used one had one of those. So
the decision was easy.

I will try your tentative startup procedure and see how it goes. I
have yet to get a hydrometer but have located a Canadian source. A
universal version Dual-Scale Hydrometer, 0.700 to 2.000 Specific
Gravity, 0.050 Divisions, 0 to 70° Baume, 1° Division, Plain Form, is
only C$18.00; they also have methyl orange but you have to call for a
price, which I hope to do tomorrow.

I will keep the list posted. Your continuing flow of information is
great and I do appreciate it and your timne and effort.

Grant

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

>
>
> grantfair2001 wrote:
> > Wow, you have been hard at work. Congratulations on your findings.
> >
> > I just bought a new Grade B burette on the weekend and it shipped
> > today <g>. (I had decided to put off procrastinating . . .)
>
> The price here in Australia for basic class B burette is about AUD$55
>

http://www.brand.de/images/download/prospekte/cat_engl/2%20gk600eng_81-108_=
vol-instr.pdf
[snip]

Umm.. you can buy Copper Chloride powder and mix it with water+HCl.
It's a lot easier and you can obtain a more accurate concentration right away.
http://www.techfreakz.org/cucl2/?slide=2

~Rolan

--- In Homebrew_PCBs@yahoogroups.com, Adam Seychell

>
>
> I'm still not sure on the best way to prepare the etchant. Weigh
> some scrap copper wire for about 150 g/l final etch solution.
> Place in yor ready to go etching tank and pour in some 10% HCl so
> the copper is half immersed. Leave it for a few days, You'll see
> the copper form thick coating of blue copper hydroxide on bits
> exposed to air. The liquid will go dark brown and the copper
> immersed will be reddish and partially etched. Add more
> concentrated HCl (30% to 37% wt) and dissolve the blue copper
> hydroxide. Keep adding some HCl every day, the solution should be
> very dark brown.
> After about 3 ~4 days, and the copper is fully immersed with acid
> then turn on the air sparger. The idea is to etch the remaining
> copper. Its a bit tricky to know when to add more acid and/or
> water, I guess you can do a copper(I) chloride test as I
> described in my previous post. If very high copper(I) is evident
> after 10 hours of sparging then it means there is low acid. The
> bubbling may take 1 or 2 days to dissolve all the copper. You
> don't want too high of acid during the preparation. If you can't
> do titrations and keep the HCl below 3.7%, then there are other
> signs to look for, such as irritating HCl fuming from the
> sparger, or if too low, there will be excessive copper(I), or
> even signs of copper hydroxide precipitate on the surface of the
> solution, when the HCl has reached to zero.
> When all the copper is dissolved then you need to add the
> necessary water and HCl to bring up the desired volume.
> Check with hydrometer for sp.gr about 1.26 ~ 1.29

Yeah, and my tank will hold up to 34 litres, and the Canadian chemical
supplier I found will sell me CuCl for $175/lb. Even 5 litres worth
would be beyond my means!

Grant

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

>
>
> rolanyang wrote:
> > Umm.. you can buy Copper Chloride powder and mix it with water+HCl.
> > It's a lot easier and you can obtain a more accurate concentration

right away.

> > http://www.techfreakz.org/cucl2/?slide=2
> >
> > ~Rolan
> >
>
> Just think 5 liters of etchant at 150g/l of dissolved copper then
> you'll need to 4.4 pounds of CuCl2.2H20 or 5 pounds cost you
> 5*$39 = US$195 if you buy from http://www.artcraftchemicals.com

grantfair2001 wrote:

> Wow, you have been hard at work. Congratulations on your findings.
>
> I just bought a new Grade B burette on the weekend and it shipped
> today <g>. (I had decided to put off procrastinating . . .)

The price here in Australia for basic class B burette is about AUD$55
http://www.brand.de/images/download/prospekte/cat_engl/2%20gk600eng_81-108_vol-instr.pdf

>
> So - to start out, if I get this right, I can prepare a

solution of

> 0.1 to 0.5 Moles/liter (0.4% to 1.6% w/v HCl) and start etching?

plus the 150 g/l of dissolved copper(II) as copper chloride :)


I'm still not sure on the best way to prepare the etchant. Weigh
some scrap copper wire for about 150 g/l final etch solution.
Place in yor ready to go etching tank and pour in some 10% HCl so
the copper is half immersed. Leave it for a few days, You'll see
the copper form thick coating of blue copper hydroxide on bits
exposed to air. The liquid will go dark brown and the copper
immersed will be reddish and partially etched. Add more
concentrated HCl (30% to 37% wt) and dissolve the blue copper
hydroxide. Keep adding some HCl every day, the solution should be
very dark brown.
After about 3 ~4 days, and the copper is fully immersed with acid
then turn on the air sparger. The idea is to etch the remaining
copper. Its a bit tricky to know when to add more acid and/or
water, I guess you can do a copper(I) chloride test as I
described in my previous post. If very high copper(I) is evident
after 10 hours of sparging then it means there is low acid. The
bubbling may take 1 or 2 days to dissolve all the copper. You
don't want too high of acid during the preparation. If you can't
do titrations and keep the HCl below 3.7%, then there are other
signs to look for, such as irritating HCl fuming from the
sparger, or if too low, there will be excessive copper(I), or
even signs of copper hydroxide precipitate on the surface of the
solution, when the HCl has reached to zero.
When all the copper is dissolved then you need to add the
necessary water and HCl to bring up the desired volume.
Check with hydrometer for sp.gr about 1.26 ~ 1.29

grantfair2001 wrote:

> The price for my Grade B, teflon stopcock 50 mL burette was $48.00
> Canadian, which equals AUD$55.

thats what I paid :)

>
> I will try your tentative startup procedure and see how it goes. I
> have yet to get a hydrometer but have located a Canadian source. A
> universal version Dual-Scale Hydrometer, 0.700 to 2.000 Specific
> Gravity, 0.050 Divisions, 0 to 70° Baume, 1° Division, Plain Form, is
> only C$18.00; they also have methyl orange but you have to call for a
> price, which I hope to do tomorrow.
>
> I will keep the list posted. Your continuing flow of information is
> great and I do appreciate it and your timne and effort.
>

thanks, you can use kitchen scales to measure out the copper
wire. Sometimes copper wire strands are coated with lubricants
and certain stuff. I once found a lot of floating rubbish in the
acid once it started etching, which I think was from coatings on
the wire. When you get the required mass of copper, give it soak
in a little hot dishwashing detergent or degreaser, then wet it
with some HCl and it should go pink, then give a final rinse.

Good source for scrap copper is scrap metal recycler. All the
scrap metal places I have ever visited have had a huge piles of
copper power cables. They sell it at about AUD$6/kg.

The universal hydrometer you describe is probably a bit
inaccurate for copper measurement. An error of +-0.05 is too
high. I would recommend you get a 1.200 to 1.300 +-0.002
They sell for AUD$26 here in Australia.

Of course once you have everything up and running, you might like
to make a mini float out of plastic that permanently sits in
your tank. That will determine if the solution is above or below
the 1.28 g/cm^3 level.



Adam

rolanyang wrote:

> Umm.. you can buy Copper Chloride powder and mix it with water+HCl.
> It's a lot easier and you can obtain a more accurate concentration right away.
> http://www.techfreakz.org/cucl2/?slide=2
>
> ~Rolan
>

Just think 5 liters of etchant at 150g/l of dissolved copper then
you'll need to 4.4 pounds of CuCl2.2H20 or 5 pounds cost you
5*$39 = US$195 if you buy from http://www.artcraftchemicals.com