Simultaneous Measurement for Thickness and P Content of an Electroless Ni/Au Plating Film on Printed Circuit Board by XRF Spectrometry

Abstract

X-ray fluorescence spectrometry (XRF) is one of the methods to measure the plating thickness. It is widely used for the quality control of plating, because it can measure the film thickness of multilayer plating and the composition of alloy layers with nondestructive and contactless method. Thus, XRF thickness analyzers are available today. Printed circuit boards (PCBs) are one of the targets of an XRF thickness analyzer. The common structure of PCBs is Cu/Ni/Au, the Ni and Au double layer plating on a Cu circuit layer. Recently, electroless nickel plating is used widely instead of electric nickel plating because of various requests from electric product manufacturers. The electroless nickel is an alloy of nickel and phosphorus, and the phosphorus concentration is important for plating quality control. However it was difficult for XRF thickness analyzers to measure the nickel layer thickness and the phosphorus concentration without removing gold plating. We have newly developed a correction method for simultaneous measurement of the respective Ni and Au layers thickness and the phosphorus concentration using XRF. We report on the latest cases of measuring the plating layer thickness and the phosphorus concentration of PCBs with our new developed method.