Homebrew PCBs

Hi Adam-

I took the lid off the tank as planned 2 nights ago. By noon today I
saw little change. The etchant was clear, the copper wire in the
etchant was shiny and looked just as it did before it went in, and the
wire above the etchant surface is a bit more covered with a cloudy
film a bit darker shade of copper than the shiny wire. There was a bit
more blue stuff on the copper, but this might cover 5% at most.

So, today at noon I added about 1/2 litre HCl to the tank. I did pour
it over the wire which was exposed. Much the of the blue color turned
dark brown. The etchant took on a very light shade of green. It was so
light that I wasn't sure whether I was imagining that.

Tonight I got a half litre of 3% hydrogen peroxide. Almost immediately
upon pouring it in, the green color became much more distinct, a
substantially darker shade which was a clear but unmistakable green. 

I then added some more 30.5% HCL. By now I have added roughly 2 litres
more acid to the original tankful of 10% HCl. The etchant darkened
some more still; it is still that clear green color. For the first
time I saw that the copper wire in the etchant was changing color. Most
of the wire under the etchant became a dark grey or brown color with a
dull texture; some was a lighter grey.

When I poured the last glugs of HCL I did not need to put my nose in
the conbtainer- it was briefly fuming around the area I had poured the
acid in, all in one spot. This stopped in under a minute.

I had a source (Cole Parmer- LabCo) for a hydrometer with .002
divisions, from Sp Gr 2.00 to 4.25 for C$16.00. However, they charge
an extra $25 for orders under $100, so I have been looking elsewhere,
hoping that I would find a better deal, but no luck to date. In
addition I learned that chemicals are not carried By COle Parmer here,
although they do in the U.S. So I haven't checked the copper
concentration in the etchant. 

Anyone in Canada want to go in together on a Cole Parmer order so we
can spend $100 on eqipment and save that 25$ add on?

I assume the process is working o.k. What do ya think? Can I add more
hydrogen peroxide (if I can get it cheaply - at $3 for 450 mL the
drugstore stuff is too expensive) and/or acid?

Grant

--- In Homebrew_PCBs@yahoogroups.com, Adam Seychell
<adam_seychell@y...> wrote:
> Hi Grant.
> How is the copper reaction going ? What color is the acid 
> solution now ? Can you smell HCl when you put your noise in the 
> container ?
> 
> I'm testing the procedure once again on small scale to get a 
> better idea. I've got 12.3 grams of 0.7mm copper sheet about half 
> immersed in 40 ml of 10% HCl, in a beaker. I'll let you know how 
> it goes. Temperature here is 8°C (night) ~ 17°C (day).
> 
> For holding a PCB vertical I use a piece of 20 mm PVC electrical 
> conduit. I cut a slit length ways into one end of the pipe using 
> a wood hand saw. I heat the end up so its just a tad soft and 
> push a piece of PCB material edge on into the slit. Then I 
> immediately cool under water and it leaves an gap equal to the 
> PCB width. It seems to make a tight fit with the PCB when cold. 
> I'm getting a digital camera soon so I'll be able to take some 
> pictures. Especially of the copper reactions in HCl.
> 
> The Rex web page mentions about horizontal etching being much 
> better in terms of uniformity. I have never tried this method but 
> I know from experience that vertical bubble etching does not 
> produce good uniformity. The only disadvantage I can see in 
> horizontal float etching is it being limited to single sided 
> action which doubles your etch time. However, horizontal float 
> etching may produce more aggressive agitation at the copper 
> surface . I would imagine bubble distribution is critical.
> 
> Adam