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July 1998

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Subject:
Re: Re[2]: [TN] Au/Ni/Cu PROBLEM
From:
Lenny Kurup <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 10 Jul 1998 12:19:57 -0400
Content-Type:
TEXT/PLAIN
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TEXT/PLAIN (99 lines) 
I agree with Matt, 4 microns of electroless nickel is sufficient to provide
a diffusion barrier for the copper, and will solder well, porosity issues
is not the culprit, in this situation. The problem is with your rinse water
and/or air environment.


Lenny Kurup 
EMX Enterprises Ltd



On Tue, 7 Jul 1998 [log in to unmask] wrote:

>      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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