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.

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 
>
>***************************************************************************
>* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
>***************************************************************************
>* To unsubscribe from this list at any time, send a message to:           *
>* [log in to unmask] with <subject: unsubscribe> and no text.        *
>***************************************************************************
>
>
>
D. Rooke
([log in to unmask])

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to:           *
* [log in to unmask] with <subject: unsubscribe> and no text.        *
***************************************************************************