Homebrew PCBs

grantfair2001 wrote:
> 
> Hi Adam -
> 
> An automated process would take the tedium and time out of it. But do
> you know of sensors up to the job? A SG sensor might not be too hard
> to improvise. But molarity?

A simple float might be done with a block of polyethylene plastic with a 
small stone tied to it somehow. But the S.G is fairly slow changing and 
doesn't require frequent measurement so using hydrometer will not be a 
problem, and you know its accurate. The hydrometer will be essential 
when mixing/making your first batch of etchant.

Acid molarity is best done by titration. You don't need indicator since 
your end point is the first signs of the copper precipitate. In fact 
one of the technical staff at http://www.oxfordvue.com  told me in a 
email that titration of copper chloride etchant should only be done 
using the copper hydroxide precipitate for end point detection. He said 
the high copper levels interfere with pH and causes most indicators not 
to work. I tried eye dropper method but the drop size of etchant is 
about 1.5 times volume that of sodium hydroxide. Counting drops is very 
inaccurate. Instead I use a 1.0 cm^3 measuring pipette and a pipette 
sucker. Take 1.0 mil of etchant into about 20 cm^3 tap water, then 
titrate with 1M NaOH solution, until I see first signs of precipitate. 
Note that towards the end point the solution must be mixed and the NaOH 
added slowly so make sure all the acid has reacted. I sometimes heat in 
a microwave oven for a few seconds before doing the titration to speed 
up the reaction of last traces of acid towards the end point.

Glass measuring pipettes and the suckers are about $2 to $3. The problem 
is only lab supplies have this kind of stuff.