I am resending his E-mail due to limited response. I would be very
interested in comment especially from electroless Ni/Au suppliers.

Dave
---------
>Recently a customer of ours has inquired as to what methods are recommended
>to determine solderability of non-electrolytic Au/Ni pwb's. In our
>discussion this customer claimed that immersion gold boards, as manufactured
>by the pwb manufacturer, soldered just fine, however during shipment and/or
>storage at the assembly site, solderability was degraded to a point that the
>colour of the solderable surface was, and I quote, "green in colour". I
>assume that this was due to oxidized Nickle migrating through the gold.
>
>Sounds like very low (<2-3 min) immersion thickness, and nickel migration 
>
>
>It seems from the posting listed below that immersion gold finishes are
>intrinsically flawed from the perspective of solderability.
>
>Can anyone in electroless 'cyberspace' recommend answers to these questions? :
>
>1)  What solderability test methods are recommended for these products?

>2) Is the IPC in the process of capturing these requirements?

>3) Is there an 'optimum' manufacturing/storage condition to minimize or
>hopefully eliminate solderability concerns?

>4) Is it implied that only ONE soldering process can be used with immersion
>gold finishes thereby precluding the use of double sided SMD?

>5) How accurate is the measurement of gold in the ranges typically quoted in
>immersion gold thicknesses (ie 2-6 microinches)? Is this measured by weight
>gain? XRF? 

>
>Thanks for your feedback...
>
>Dave Rooke
>Circo Craft - Pointe Claire
>[log in to unmask]
>
>____________________ reply separator _______________________
>>
>>|      Hi!
>>|      
>>|      Accelerated aging factor for a new PCB surface finish? 
>>| Do you mean 
>>|      oxidation? Intermetallic growth? What type of finish? 
>>| Please send 
>>|      additional detailed info covering your request.
>>|      
>>|      
>>|      
>>|      Dave Hillman
>>
>>Hi Dave, 
>>
>>In this case the new PCB suface finish is electroless Ni/immersion Au. And 
>>you are right, it is oxidation - under extreme and/or even normal storage 
>>condition, Ni has the tendency to diffuse through Au layer (if there is 
>>any porosity) and gets oxidized on the top of Au layer, then the 
>>solderability will be affected due to the existance of nickel oxide on the 
>>top of Au layer.  
>>
>>So far I have not found any mathimatical model (either physical or 
>>experimental)for acceralated aging factor as the function of time in aging 
>>chamber, temperature in aging chamber, and relative humidity level in 
>>aging chamber, although I have found several aging method.  But none of 
>>them provide corresponding aging factor.  By aging factor, I mean the 
>>ratio between the time in chamber and the time in normal storage 
>>environment, with same level of solderability degradation.
>>
>>Thanks in advance for your advice.
>>
>>
>>Nora 
>>
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>>
>D. Rooke
>([log in to unmask])
>
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D. Rooke
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