RoHS screening by XRF provides information about the chemical content of the components being tested. In the case of homogeneous materials such as plastic housings, XRF will provide quantitative chemical analysis at the RoHS levels for most materials. In cases where the material is not homogeneous, such as electronic assemblies and PCB assemblies, XRF will provide semi-quantative or qualitative analysis. The more complex the sample the less quantitative the results will be.
In a recent study conducted by the National Physics Laboratory in the UK, they concluded that most electronic components contain either less than 500 ppm of the restricted elements or more than 2000 ppm. Thus, very few measurements will determine values very close to the 1000 ppm limit.
In addition, one of the largest risks of RoHS violation is that the components are soldered with 60/40 Sn/Pb solder instead of a lead free solder. Moreover, all materials being tested should have known concentrations of the restricted substances. Thus, XRF analysis can be used to give an indication that the restricted elements are present or absent – used to confirm the MTR for the parts being tested.
In cases where there is a discrepancy from the MTR or there is an indication that the part under test is not RoHS compliant the part can be either rejected or sent to the laboratory for further testing – depending on the company policy.