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.
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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
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