Repeatability Analysis of EDXRF Equipment for RoHS Compliance Screening for Soldering Materials used in PCBA Manufacturing

With the enactment of the European Union (EU) ROHS Directive 2002/95/EC, certain electrical and electronic products that are manufactured in or exported to the European Union have restrictions on the use of lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyl (PBB) and polybrominated diphenyl ethers (PBDE). EDXRF (Energy Dispersive X-ray Fluorescence) is one of the methods that can be used for RoHS materials ´screening´. EDXRF has the advantage of simple or no sample preparation as well as being non-destructive with a relatively short testing time but it has disadvantages such as elemental matrix interferences. EDXRF ´screening´ results need to be carefully analyzed or verified as the limits for lead and the other elements for ROHS compliance are very low. This paper describes the work done on the testing of SnAgCu, SnCu and SnPb solder samples with EDXRF equipment to determine accuracy and repeatability of measurements for lead, silver and copper. The samples used included certified solder reference samples and solder samples taken directly from production wave soldering and mini-pot rework solder fountain machines. The testing was done using multiple models of the same EDXRF equipment across over 43 manufacturing locations globally. The advantage of using a large number of test equipment gave an assessment of not only solder measurement accuracy and repeatability but also accuracy and repeatability of multiple EDXRF machines of the same model. The results will be discussed in relation to the IEC TC 111 Working Group 3 Draft Standard Acceptance criterion.