To answer these questions ERA carried out an investigation of a standard desktop system. This was kindly provided by manufacturer Shimadzu via Kratos Analytical, their UK agent.

ERA looked at samples ranging from simple bulk flat alloys to real electronic components - the sort which will require analysis by RoHS. Simple and large samples such as the base of a light bulb (see Figure 1) can be analysed with ease.

ED-XRF indicates 64% of lead (discounting light elements C & O which this technique cannot detect). However, the sampling area of the ED-XRF beam is 10mm in diameter - hence both the contact and the surrounding insulation are analysed as a whole. Discounting the signal from elements in the insulation (Si, Ca), one can see that the lead forms approximately 93% of the contact.
		Figure 1. ED-XRF analysis of the base of a light bulb

This indicates that this is probably a high melting point solder and hence a RoHS exempt application. (NB The copper signal is from a wire contact to the filament within the base of the bulb).

	Other components are less easy to analyse. Figure 2 shows an ordinary through-hole mounting potentiometer. Analysis of this device showed large quantities of bromine (indicating a flame retardant -but providing no information on whether this is a restricted form) and calcium (a filler in the plastic. However, this device is not lead free and this fact is only revealed by destructive analysis of the contact surface when the device is broken open (Figure 3).
Figure 2. Through-hole mounting potentiometer
	ED-XRF analysis now reveals 7% lead and 0.2% cadmium but, owing to the resolution, cannot reveal where these banned materials are present. High resolution x-ray fluorescence analysis in ERA’s scanning electron microscope reveals that the lead (37% by weight) is in the solder and the cadmium (1.3%) is in the silver contacts.
Figure 3. Internal contact surface of the potentiometer

This study has shown that ED-XRF has real value as a screening technique for RoHS restricted substance detection and also for quantitative analysis. In either case, however, a clear understanding of the limitations of the technique and an appropriate procedure to apply it are essential if serious errors are to be avoided.