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September 2010

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Subject:
From:
Mike Fenner <[log in to unmask]>
Reply To:
Date:
Tue, 21 Sep 2010 17:02:02 +0100
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text/plain (341 lines)
I was going to say, my understanding of the P addition was to modify the
grain/plated properties of the NI, to give good mechanical properties rather
than directly as a solderability control, but Werner's answer covers that
and rather more! As is his norm.
There are proprietary "solderable" Ni plates. Solderable meaning less
readily/more slowly passivating, but these are more usually employed on
structural assemblies like large heat sinks, packages rather than PCB
finishes. For regular PCB finishes the N is protected to maintain
solderability with thin Au - to give us ENIG, or sometimes Ag or even Sn. 
[I personally do not consider that Pd containing finishes protect or improve
solderability.]

Regards
 
 
Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Tuesday, September 21, 2010 3:40 PM
To: [log in to unmask]
Subject: Re: [TN] Solderability of nickel plating

 Hi Kevin,
Now my 5 cents.
From my experience, I do not see solderability directly linked to the
concentration of phosphorus co-plated with the nickel-I see however, brittle
interfacial failures between the Ni-P surface and the Ni3Sn4-intermetallic
compound which directly track with P-concentration at that interface. The
presence of Ni3Sn4-IMC is clear evidence that there was no solderability
issue-it is the concentration of the P at the interface which weakens the
interfacial bond. 
Because of their superficial appearance, conditions with both too much P and
too little P [causes hyper-galvanic corrosion along the grain boundaries of
the Ni plating] have been termed 'black pad.'
Having too much P at the interface can be the result of improper Ni-plating,
but also the result of too much Ni being dissolved in the Sn of the solder
leaving to much P behind-this can happen from too many soldering operations.
Werner

 


 

 

-----Original Message-----
From: Glidden, Kevin <[log in to unmask]>
To: [log in to unmask]
Sent: Tue, Sep 21, 2010 8:52 am
Subject: [TN] Solderability of nickel plating


All,



Can anyone comment on the solderability of the nickel plate, particularly
with 

regard to type of plating: high phosphor / low phosphor, and also storage 

conditions:



I've been gathering info, and seen conflicting information.



From one article: http://corrosion-doctors.org/MetalCoatings/Electroless.htm



A paper submitted at the Electroless Nickel conference of 1989 held in 

Cincinnati Ohio, Titled "Solderability Parameters of Elecroless Nickel
Bearing 

Electronic Finishes" By Louis Kosarek of STB Systems, Inc. report that "An 

electroless nickel deposit which contains a concentration of phosphorus
ranging 

from 0.1% to 3.0% is readily solderable on an "As-plated Basis" per Mil-Std
883c 

method 2003. The frequency of solderability tests which fail per Mil-Std
883c 

will increase as the phosphorus content of electroless nickel alloy
increases 

from 3.0 to 7.0% phosphorus. A solderability test conducted per Mil-Std 883c


method 2003 incorporating an as-plated surface finish containing phosphorus
in 

excess of 7%, the components will consistently fail. The mode of failure is 

non-wetting of the surface."

This indicates low phosphorous plating is best for solderability.  Many
other 

papers seem to agree with this.



----------------------------------------------------------------------------
-----------------------------------------



From another article: http://www.pfonline.com/articles/pfd0024.html



Solderability/Weldability.  An important aspect of electroless nickel to the


electronics industry is its solderability. All electroless nickel deposits
are 

solderable provided the soldering conditions are matched to the condition of
the 

particular electroless nickel deposit. Lower-phosphorus electroless nickel
is 

more easily solderable immediately after plating than higher-phosphorus 

electroless nickel. However, this advantage disappears after 12 - 24 hrs. At


this point, the ease of solderability depends upon the characteristics of
the 

passive layer that forms on the surface of the electroless nickel deposit.
Those 

deposits plated from baths containing heavy metal and sulfur-bearing
brighteners 

and stabilizers, such as most commercial low- and mid-phosphorus electroless


nickel systems, form a thicker tenacious passive layer than those that do
not, 

such as most high-phosphorus electroless nickel systems. High-phosphorus 

electroless nickel systems tend to be more solderable in aged deposits.



Other important factors influencing the solderability of electroless nickel 

deposits include residual contamination left on the surface after plating
and 

storage conditions after drying. Surface contamination and exposure to 

environments containing sulfur dioxide, chlorine, high humidity and high
ambient 

temperatures will detrimentally affect solderability. Therefore, it is 

imperative that parts be thoroughly rinsed in clean DI water, dried and
stored 

in a cool, dry atmosphere, preferably nitrogen.

This article indicates high phosphorous plating is best for long term 

solderability, and also that parts must be stored carefully (cool, dry,
sealed, 

nitrogen).  Other articles seem to state this is a highly stable finish and
is 

even used as a corrosion inhibitor.



Thanks,





Kevin Glidden

Manufacturing Engineer

Astronics Luminescent Systems Inc.<http://www.astronics.com>

4 Lucent Drive

Lebanon, NH 03766

(603) 643-7766 x3152



Please note, LSI operates on a 9/80 work schedule, and is closed on
alternating 

Fridays.  Please click the link provided to view the days LSI will be
closed.

http://www.astronics.com/LSI/documents/2010calendar-NH.pdf



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