>
> got a question
> is it attack only copper or also tin (tin as resist after patern
> plating)
>
> gr. Roel
To my knowledge the only etchants known to be compatible
with tin metal plating resists is the ammonia alkaline type.
ALKALINE AMMONIA CHLORIDE ETCHANT:
∗ cupric chloride
∗ aqua ammonia
∗ ammonium chloride
pH > 8
If it has a slight ammonia smell at room temp then pH is
high enough. Copper content is monitored by specific gravity
and must be kept between an upper and lower limit during
normal operation.
Sorry, I don't have the S.G. numbers or concentrations of
ammonium chloride at the moment.
This etchant cannot be regenerated via electrolysis, due to
chloride content. Regeneration is by dissolved air, ammonium
chloride, and ammonia. The ammonium chloride and ammonia is
required by regeneration reaction of dissolved oxygen (from
air). This etchant is very fast, comparable to fresh ferric
chloride.
CONTROL:
When solution stops smelling or pH < 8 then add some 25%
aqua ammonia.
When S.G. goes too high, you add water.
When etchant slows down and pH > 8 and S.G. is in range then
you add ammonium chloride. There are probably better ways to
identify when ammonium chloride is required. I don't have
the experience with this etchant to know. I've only "played"
around with it in small beakers.
FURTHER READING:
see
http://www.pcbfab.com/iepart5.htmlsee
http://www.pcbfab.com/iepart3.html