PCB007 Magazine

PCB-Jan2014

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f e at u r e Determining Phosphorus Content in EN Plating Using XRF Spectroscopy by Michael Haller, Jim Bogert and Ryan Boyle Fischer Technology and Volker Rößiger and Wolfgang Klöck Helmut Fischer GmbH Abstract Electroless plating processes are popular because of their performance, reliability and costeffectiveness. The process combines unique deposit properties such as uniform plating buildup 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 38 The PCB Magazine • January 2014 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. 1. Introduction Phosphorus, the concentration of which significantly influences the mechanical and magnetic properties of the coating, is incorporated during electroless or chemical nickel deposition[1]. For this reason, measurement of the phosphorus content has been an important issue ever since electroless nickel deposition methods were introduced. As an alternative to the established wet-chemical methods, during which the coating is dissolved and therefore destroyed, non-destructive and simpler methods are desired. XRF provides such a non-destructive test method, where utilisation of the characteristic emissions of P-K radiation can

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