Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, lists <stuart.winsor.lists@d...>
wrote:
> In article <dgk7mo+jbtb@e...>,
>    Andrew Mawson <andrew@m...> wrote:
> > Along with my multi tank system I acquired some Mega (Seno) 600-021 
> > immerse tinning solution - it's  rather old but I'll try it anyway !

Some tin plating solutions have a rather short shelf-life.  Use a 
little caution if it doesn't work well.

> > On the bottle it says to disolve in tap water at 50 deg C - let it
> > cool 
> > and use at room temperature. On the Mega site it says to disolve in 
> > distilled (rather than tap) water. Two questions:
> 
> > a/ should it be distilled or tap water?

The problem with answering this question is it really depends on
the quality of your tap water.  Certain areas have tap water that 
is fairly "soft" and doesn't contain many dissolved minerals.  Other
areas have tap water that is very "hard" and contains many dissolved
minerals.  Depending upon the quantity and type of the dissolved 
minerals, the plating may or may not work.  Thus, it's safest to use
distilled water, which is of known quantity.  You could try it with
tap water, and if it works for you, that would let you save a few
pennies (US$.01) per board.

> I've used tap water with this, or a similar, product and it works ok
but I
> notice there can be a slight milkiness or precipitation when mixed
up and
> I wondered whether this was a reaction with chemicals in the water.
It may
> of course depend on the purity of your tap water and it is possible that
> the salts present in "hard" water may interfere with the plating process
> in some way.

Carbonates are rather notorious for wanting to cause percipitates.

> Generally speaking pure water of some sort is better for making up most
> chemicals

Pure water is a known quantity.  Tap water varies between different
areas, as well as during the year even within the same area.

> > b/ what is the odd chemistry that lets it work at room  temp but
not at
> > 50 Deg C when increasing the temp normally speeds up chemical
reactions.
> 
> It is likely that the chemistry works adequatly at room temperature and
> higher temperatures would lead to rapid and uneven deposition, possibly
> with poor adhesion. You may even get decomposition rather than
plating in
> the presence of the copper.
> 
> I believe the chemistry involves Thiourea which is considered a health
> hazard and the risks may be higher if it is warmer than neccessary.

There are a number of tin plating solutions available, some of which
have absolutely dangerous chemistries.  I remember using one from
about 25 years ago that was based on Sodium Cyanide, Stannous 
Chloride, and Sodium Hydroxide.  Talk about a real witch's brew!

> The higher temperature is neccessary to get the stuff to dissolve
properly
> in a reasonably short time.

Any type of plating process, whether it's electroplating or 
electroless plating is more of an art than a science (and, a black
art at that!).  

> Stuart

Dave