Rudy -
     I'm surprised to hear that you think 4 microns of nickel is thin.  
     This is 0.16 mils, & many people specify down to 0.10 mils.  You're 
     suggesting putting on almost « mil of nickel (2-3X of 4 microns)?
     
     
     Matt Byrne
     Hadco-Owego

______________________________ Reply Separator _________________________________
Subject: Re: [TN] Au/Ni/Cu PROBLEM 
Author:  "TechNet E-Mail Forum." <[log in to unmask]>  [log in to unmask]  at 
INTERNET-OWEGO
Date:    7/5/98 10:23 AM


In a message dated 98-07-05 03:46:42 EDT, you write:
     
<<
 I am a PCB fabricator in the UK and when we started using the electroless 
 Nickel and Immersion Gold process we noticed a curious phenomenon. If the 
 panels are immersed in DI water or mains water after processing, then 
 exposed to air for a minute or two before drying, the gold has reddish brown 
 stains in random areas. Although this did not seem to affect solderability 
 to any noticeable extent, it was not cosmetically attractive.
     
I would like to have an explanation for this mechanism. The immersion gold
 is 0.15 microns max (6 millionths of an inch) over 4 microns (0.00016") of 
 electroless nickel. As this occurs with DI or mains water, contamination of 
 the water does not seem to be a factor, but simply exposure to air at room 
 temperature when the surface is wet. >>
     
     
Paul:
     
Given the thiness of the EN (and Au), I would bet the problem is likely one of 
porosity, and having some exposed Copper here and there.  And porosity driven 
by our industry's great nemisis, galvanic corrosion, would give you exactly 
what you are seeing.
     
Further, I would bet that thicker EN ( 2-3X) would stop the problem.
     
Rudy Sedlak
RD Chemical Company
     
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