Homebrew PCBs

Volkan Sahin wrote:
>  
> 
> Hi Simao,
> Thanks a lot for your reply. It contains full of information. I tried 
> phosphoric acid + ammonium per-sulfate it works fine. It didn't etch the 
> tin plated side of the copper. The problem is ammonium per-sulfate is 
> very slow etcher and tin becomes black.  I'll try Adam's wet lamination 
> method, I think it will  reduce pressure change inside the holes.
> 
> Regards,
> Volkan 

A long time ago I tried doing what your doing. I couldn't get persulfate 
etchant to stop attacking the tin plating. I found that if I left the 
tin in dry air for 24 hours then an invisible oxide coating would form 
and could prevent complete etchant attack. The tin would be still be 
dark and patchy. I concluded it wasn't going to work. I think the 
phosphoric acid helped, but it wasn't what I called a successful fix. 
Alkaline etchants is the only way to go for pure a tin metal resists.

Normal practice it to use solder metal resist with persulfate or 
sulfuric peroxide etchant, and then reflow the solder in an oil bath.

Adam