Orientation anomalies in plating thickness measurements from advanced packaging substrates

Abstract

Experiments show that serious anomalies arise in the measurement by XRF of film thickness in bond fingers on packages. The anomalies can be exposed as a package orientation dependence in the film thickness measurement. The orientation anomalies occur on translation of the specimen between rows of bond fingers. The anomalies are due to either primary fluorescence or to scattered radiation from the substrate with an escape path to the detector. In bond fingers consisting of Au, Ni and Cu, primary fluorescence of substrate Br enhances the Au signal, while scattering of W characteristic lines enhances the Ni signal. The anomalies can be overcome by ensuring that the bond finger lies in the plane containing the x-ray source and the proportional counter detector so that substrate emissions are buried. Instrumental improvements are also suggested.