Hi Neil,
Are you sure the gold thickness is 0.014 microns, the minimum gold
thickness, to afford the nickel good tarnish protection, is 0.15 microns.
With such a thin layer of gold, the underlying nickel will surely get
tarnished and create solderability problems. You mentioned nickel pits,
exposing copper beneath, this means that copper will bloom to the surface
of the gold and tarnish over time, compounding the solderabilty problem. A
good nickel thickness is 4 microns, to provide a good anti-diffusion layer
for the copper through gold and to afford good solderability.
Review your electroless nickel/immersion gold process. Control of the
process is very important, speak to your supplier to have them audit the
line and make recommendations on controlling the process. You surely are
not obtaining good quality.
Good Luck,
Lenny Kurup
EMX Enterprises Ltd
Markham, Ontario, Canada.
On Wed, 15 Jul 1998, Neil Atkinson wrote:
> Thanks to Ron Hayashi for his reply regarding shelf life of immersion
> gold PCBs.
>
> The boards I have experienced problems with are coming up to 18 months
> old (I tend to agree with Ron that 6 months is about the maximum shelf
> life) but I have also looked at the thickness and quality of plating.
> The gold on the board is 0,014 microns thick using XRF equipment (is
> this OK?) I thought that seemed quite thin!?
>
> I have witnessed 'pitting' in the nickel layer which, in some cases,
> goes right down to the copper.
>
> Can anyone tell me how much nickel / gold should be on the board and
> what effect the above would have on solderability / shelf life
>
> Thanks,
>
> Neil Atkinson
>
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