Hi Kevin - yes, there is a considerable pile of industry data that is in
agreement with the information you listed. The lower the phosphorous
content, the more inherently solderable the nickel coating will be.
However, there is no free lunch, the lower the phosphorous content, the
lower the corrosion resistance of the nickel plating. Many people use a
medium phosphorous content as a balance between the two plating
characteristics. The medium phosphorous contents also tend to have less
issues with "black pad" than low phosphorous contents although there is
not an industry consensus on that statement. A "rough" breakdown of the
phosphorous content ranges would be Low: 1-5, Medium: 5-9, High 9-12 and
there is considerable discussion on the breakpoints between the 3 levels.
The characteristics of the flux being used in the soldering process is the
key parameter to achieving a good solder connection. Nickel oxide requires
a good flux to break it down. Also, a much better solderability
specification to use instead of the MIL-883, mthd 2003 would be IPC
JSTD-003.
Dave Hillman
Rockwell Collins
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[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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