Regarding Solderability of Au/Ni plate printed circuit boards

The solderability of Au/Ni plated boards depends on the properties of
two interfaces. The top gold layer and the interface between gold and
nickel. We have also found that copper is dark horse in this subject as
pointed out by Allen Hertz. It is not only copper in the nickel layer
that cause trouble the copper will also spread into the gold layer. We
published a paper at ISHEM Indian about this matter. We have observed
that the solderability correlate with the amount of copper in the gold
layer. For the moment we investigate this matter further and hopefully
we will have a open report available within a year.


Per Carlsson
IVF- The Swedish Institute of Production Engineering Research
Argongatan 30
S431 53 Molndal
SWEDEN
Tel Int+46 31 706 6142
Fax Int + 46 31 276130
email: [log in to unmask]
Kopia: [log in to unmask]; [log in to unmask]
Angående: ReÄ3Å: solderability test for ENIG PCB finish
Datum: den 16 december 1996 17.46


     Hi Allen -

     Did you publish your investigation results anywhere? The copper
issue
     is something I hadn't thought of but it makes sense (it's something
I
     look for in the future). The solderability/E.nickel paper I
referenced

     did show that the Phosphorus content did make a difference - lower
     phos contents had better solderability than higher phos contents.
     Fang's conclusions agreed with one quoted reference(Feldstein) but
     disagreed with a second reference (Shinohara). It would be
interesting

     to compare your data with this published data to see what test
     difference's appear.



     Dave Hillman
     Rockwell Collins
     ddhillmaÉcacd.rockwell.com



______________________________ Reply Separator
_________________________________
Subject: ReÄ2Å: solderability test for ENIG PCB finish
Author:  TechNetÉipc.org at ccmgw1
Date:    12/16/96 10:12 AM


Dave,
Very valid points!

Technet,

I would like to add one finding pertaining to solderability of
electroless
nickel - gold: Most have assumed the Phosphorus level is a major
contributor to
the solderability of this surface finish. Experiments completed in my
past
life
have demonstrated that the nickel application process removes a portion
of
the
copper, placing trace amounts of copper into the bath. Upon saturation,
the

copper is then re-depositied embedded in the nickel. The embedded copper
oxidizes, making the surface unsolderable. Varying the levels of
Phosphorus
did
not effect the solderability or yields during high volume experiments!

Allen Hertz
Racal-Datacom
allen_hertzÉusa.racal.com
________________________________________________________________________
____ 
___
Subject: Re: solderability test for ENIG PCB finish
Author:  TechNetÉipc.org
Date:    12/15/96  12:04 PM

     Good Morning TechNet!

     Your method of conducting a solderability test should not change
just
     because you are not using a tin/lead finish! I suggest using one of
     the tests in ANSIJ-STD-003. With the emergence of the new
alternative
     finishes (e.g. gold, silver, palladium) the specifications are
still
     playing catch-up but the basic test methods are still applicable.
You
     may need to change a dwell time because of dissolution rates (e.g.
     palladium) or may want to use a different flux because of your
process

     (e.g. OSP type finishes) - work with your pwb vendor to have an
     acceptable test procedure both groups can use. I only have one
     reference in my pile of papers that discusses the relationship of
     solderability and E nickel but it's pretty good. Try:

     "Factors Influencing Solderability Of Electroless Ni-P Deposits",
Jing

     Fang, Plating & Surface Finishing, pages 44-47, July 1992.

     Good Luck

     Dave Hillman
     Rockwell Collins
     ddhillmaÉcacd.rockwell.com





______________________________ Reply Separator
_________________________________
Subject: solderability test for ENIG PCB finish
Author:  TechNetÉipc.org at ccmgw1
Date:    12/13/96 10:44 PM


Dear Technetters,

 What is a quick, easy & effective way of assessing
solderability/ wettability of a PCB with electroless nickel/immersion
gold
(ENIG) finish? How does phosphorus content in the Ni deposits affect
solderability? Will a lower %P content in Ni be more prone to
passivation/oxidation & thus affecting solderability??

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