Homebrew PCBs

In commercial shops copper was almost always pattern plated followed by tin, tin/lead, or in the case of HP, nickel gold plating.  If you wanted solder mask over bare copper the tin plating was stripped after the base copper foil was etched.  Plating copper over the whole board just meant you had more to etch.   So antitarnish after copper plate was never much of a question.

The plating chemistry in most acid copper baths contained amines.  They were present to provide leveling, grain refinement and to reduce stress.  As a by product, they were pretty good antitarnish agents as well.

In your case, the best place to put an anti tarnish is in the second rinse following the plating bath.  If you have realy hard water, consider making solutions with DI water from the super market.  This was a rairity in the industry, but I did run into it a couple of times.  Citric acid at 3 to 5% by weight should do the job.  The first rinse should be a quick dip and a slosh around to remove the gross plating solution.  Let the board drain off fairly well so you don't carry much plating solution over with the board and stick it in the second rinse.  Slosh it around for a couple of minutes and rinse again in running water.  A final DI water rinse is not a bad idea.  

Monoethanol amine seems to be available over the web.  I've seen it but can't remember where.  It is much more effective than citric acid.  Again 3 to 5 % by either weight or volume (it's a liquid with a specific gravity just a bit lower than water) in the second rinse. 

----- Original Message ----- 
  From: Adam Seychell 
  To: Homebrew_PCBs@yahoogroups.com 
  Sent: Friday, December 03, 2004 5:19 PM
  Subject: Re: [Homebrew_PCBs] Cleaning copper with lemon juice


  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



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