Homebrew PCBs

Earl T. Hackett, Jr. wrote:
> 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. 
> 

Thanks for the tips Earl, I do not know what the ingredients are in the 
brightening additives I'm using, but they don't seem to help the tarnish 
problem at all. I have both monoethanol amine (MEA) and citric acid 
laying around the workshop. I'll try adding small amount of citric in 
the rinse as you suggested. There is a triple cascaded rinse tank 
following the acid copper plating. I also use these same rinse tanks for 
rinsing off the ammonium persulfate microetch. After plating, the panels 
are rinsed followed by application of dry film photoresist by wet 
lamination. Would citric acid residue effect dry film ?  MEA on the 
other hand is alkaline and will probably be fatal to dry film. I did 
read somewhere MEA can be used as dry film stripper.
I'll let you know what happens.

Adam