Direct Determination of Phosphorus Content in Electroless Nickel Plating
Developments in XRF instrument hardware and software have extended the measurement application of electroless plating processes to nearly any substrate.
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Authored By:
Michael Haller
Jim Bogert, Ryan Boyle
Fischer Technology, Windsor CT, USA
Volker Rößiger, Wolfgang Klöck
Helmut Fischer GmbH, Sindelfingen, Germany
Summary
Electroless plating processes are popular because of their performance, reliability and cost effectiveness. The process combines unique deposit properties such as uniform plating build up regardless of geometry, excellent corrosion resistance, superior hardness and wear and the ability to plate on non-conducting materials. The most commonly used electroless plating process is Electroless Nickel (EN) plating using nickel phosphorus baths.
The phosphorus content plays a fundamental role in all physical properties of the deposit. It is, therefore, critical to control the phosphorus content within a relatively tight range. X-ray fluorescence is an excellent method to not only measure plating thickness but also weight percent elemental composition of coatings. Previously, it was only possible to measure plated phosphorus content on steel substrates. New developments in XRF instrument hardware and software have extended the measurement application of electroless plating processes to nearly any substrate. The simultaneous measurement of thickness and composition is critical.
Conclusions
New developments in XRF hardware and software technology have made it possible to simultaneously measure % phosphorous and NiP coating thickness in air. Being able to measure the phosphorous content directly now allows determination of the % phosphorous in electroless Ni-plantings on substrates in addition to iron, such as, Al or even non metallic substrates. Instruments with SDDs can measure the P-K radiation quite well using soft primary excitation (10 kV, non-filtered). Coating thickness is determined using harder excitation (30 keV or 50 kV).
The information depth for phosphorus is relatively low (<1 m) due to the low energy of P-K fluorescence. Conventional indirect determination of phosphorus can still be regarded as a relatively robust method with proportional counter tube instruments - the only option with these instruments.
Initially Published in the IPC Proceedings
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