Homebrew PCBs

Earl T. Hackett, Jr. wrote:

> Not lemon juice, but citric acid was a common antitarnish when stripping print and etch innerlayers in caustic.  Amines work better as an antitarnish, but they form complexes with dissolved copper and makes waste treatment very expensive.  It reacts with the copper and forms a layer that resists oxidation reasonably well.  After stripping these boards went through a black or red oxide treatment to enhance adhesion in multilayer boards.  I seem to remember one or two shops that used citric acid in a chem clean line and I don't remember any adhesion problems with the photoresist. 


I'm having a hard time stopping freshly electroplated copper from 
tarnishing when the panels dry. The cause cannot be a sulfuric acid 
residue problem since it tarnishes even after neutralization and 
excessive rinsing with DI water.
How was the citric applied to prevent the antitarnishing ?  Do you know 
the process details for antitarnish, what is the critic acid 
concentration, are the boards rinsed before drying ?

Adam