Thanks for the update. What you describe about the gray film
on the copper surface during etching is very important
discovery. The film is copper(I) chloride that hasn't had
time to dissolve. I have found the film plays a big part in
slowing down etch rate, so I am not at all surprised it took
nearly 1 hour to etch your test PCB. Copper(I) chloride is
light gray insoluble solid, but can dissolve in solution
containing chloride ions due to a phenomenon called ion
complexing and this form of the compound look brownish
black. The formation of a copper(I) chloride film is saying
to you that the etchant needs a lot more regeneration.
An interesting trick is to take the copper with the gray
copper(I) chloride film and expose it to light and air while
wet. It dries to a brown powdery coating. Areas that are
kept dark go to gray powder.
The green droplets on the container walls would of been
there long enough time for atmospheric oxygen to oxidize the
copper(I) to copper(II) chloride. The brown droplets have
not yet had this happen.
All the signs show that things are working as expected. For
now, I would suggest passing in the current sparging setup
and wait for the air diffuser hose to arrive. Get it working
in water first, because you want to avoid pulling it in and
out of the etchant and making a mess.
Adam
grantfair2001 wrote:
> Even though my tank of etchant is far from the deep green color which
> shows it is at an optimum, I decided to etch a small board tonight. I
> hung it in the etchant above the aerator. (I drilled a hole in one
> end and hung it from an insulated wire).
>
> In about 25 minutes one half (the part closest to the etchant surface)
> was etched clear. It took another 25 minutes to get the other half
> clear. I finally had to hang it upside down to get it cleared. A
> horizontal pcb holder is in the planning stages.
>
> In the first 20 minutes or so, I noticed part of the copper on the PCB
> was light grey in color. I suspect this was CuCl(I) because when I put
> a small amount of green etchant from the tank lid on this area, it
> disappeared. This also suggests that there is lots of CuCl(I) still in
> solution.
>
> I measured the pH again with indicator paper. The paper showed red (2)
> after I emptied the second 4 litre jug of HCl into it a few days ago.
> However, today it was 3 (or higher, if the the pH is higher yet and
> the etchant is discoloring the indicator paper).
>
> Although there is green etchant on the inner surface of the tank top,
> a drop of tank etchant dropped on the same lid is dark brown. So a lot
> of CuCl(I) needs to be converted. I am waiting for some fine bubble
> diffuser hose. Unfortunately most fish farming is done on the east and
> west coasts of Canada, and I am more or less in the middle between the
> two.
>
> So things are progressing, if slowly, I am learning about the CuCl
> approach, and I have etched my first board. In spite of the long dunk
> it looks just fine with all traces intact. Because I haven't had a
> totally clear recipe to operate from, things have gone slowly. But I
> hope my experience will make it easier for anyone who wants to use
> this appraoch in the future.
>
> Grant
>
>
>
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