Hi Matt,
Im sorry, but I have to agree with Rudy, we have always and forever
used 200 microinches of nickel as a barrier, and in most cases we have not had
a problem, except with some gold porosity in the early '80's.
Respectfully,
Les Connally
> From: [log in to unmask], on 7/7/98 4:51 PM:
> 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 ½ 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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