Should energy dispersive XRF be used to determine RoHS compliance?

Energy Dispersive XRF, or EDXRF, is a quick and easy technique for measuring chemical compositions. IMR Test Labs employs this technique as a screening tool and for full quantitative testing of truly homogenous materials. However, XRF has severe limitations when it comes to the analysis of small components or samples with more than one material present. For example, a piece of steel can easily be analyzed for full compliance with XRF, but a piece of plated steel can not. The X-rays used in XRF testing penetrate through the plating and into the substrate. The signal returned is a mix of information from both the plating layer and the substrate. This introduces a lot of error into the analysis. If lead were to be present in the plating at say 1500 ppm, XRF might read this as 500 ppm due to dilution of the signal from the plating with that from the substrate. Therefore a potentially failing reading is masked as being compliant. The other problem is that XRF looks at a fairly large area ...  more