Ok, copper etchants come in many different flavors. The ammonia alkaline are
type the most commonly used for tin or tin/lead metal resists (i.e. pattern
plating). The tin forms near perfect resistance (3 um thickness) to the
ammonia type etchants, especially the sulfate based. I recommend visiting
your local university library and getting hold of a book called "Coombs'
Printed Circuits Handbook". It has many of the basics of PCB fabrication that
can start you off.
Here is the alkaline ammonia sulfate etchant I use. It is suitable for room
temp operation; Note: the high alkalinity makes it not suitable for use with
photoresists.
CuSO4.5H20 - 150 to 190 g/l (optimum 175 g/l)
25%(wt) aqua ammonia - 70% (vol.)
98% sulfuric acid - 3.0% to 4.0% (vol.)
pH should be between 10 and 11, adjust with aqua ammonia additions.
Tank must be sealed virtually air tight when not in use. Otherwise NH3 will
evaporate over time and pH drops significantly. regeneration is done with
stainless steel anodes in stagnate solution at current density between 3 and
5 A/dm2. Etch times at 25°C using air bubble agitation is 20 to 25 minutes
for 35 um copper foil. Only one place in the world I know of markets this
type of etchant, and that is the German company Elo-Chem. You won't see it
documented in many places.
http://www.elo-chem.de/html/english.htmlNo one uses electroless tin unless they have to. The tin is plated on all the
tracks directly after copper plating. Electrolytic tin plating works much
faster, cheaper, safer, more reliable, lower maintenance and more predictable
than electroless tin. The bath I use is the acid stannous sulfate type (looks
like banana flavored milk drink). See your friendly plating supplier for
necessary brighteners and chemicals.
j_hallows wrote:
> > First you should worry about how your going to etch.
>
> You read my mine this was my next question.
>
> > If you decide on
> > pattern plate then you have choice of tin or tin/lead metal resist.
> If you
> > choose tin then you must use alkaline ammonia etch. If you choose
> tin/lead
> > then can use sulfuric/peroxide, ammonium persulfate etch, or
> ammonia etch.
>
> Is this the same stuff called Liquid Tin by MG Chemicals and a
> similar prodouct by Datak? Or would these get disolved by the etching
> solution?
>
> > However, I would be wary on having toxic lead plating solutions
> laying
> > around. For the ammonia etch it can be chloride or sulfate based. If
> > chloride based then you have major waste problems because the
> copper cannot
> > be recovered easily (at least what I know) and you will need to
> treat then
> > dump your solution ($$$).
>
> This is like ferric chloride?
>
> If you use sulfate based alkaline ammonia then
> > the etchant can be electrolytically regenerated although the
> etching rate
> > is much slower than chloride.
> >
> > PCB fabrication may look simple on a flow chart but when it comes to
> > actually making it work its a whole different story.
> >
>
> Please excuse my ignorance. I have a lot zeal and a lot to learn.
>
>
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