Homebrew PCBs

> 
> 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.html
see http://www.pcbfab.com/iepart3.html