Introduction

The EUs directives on the Restriction of the use of certain Hazardous Substances (RoHS) and Waste Electrical and Electronic Equipment (WEEE) set limits on the use of Cd, Pb, Hg, Br and Cr6+ in diversely plastic products or in each homogeneous component of electrical and electronic products, for example plastic cable insulation and solder joints on a printed circuit board (PCB). EDXRF is a well-suited analytical method for direct RoHS compliance testing of various samples such as metals, plastic, powder with minimal sample preparation.

The Analytical Instrument

The X-ray MaXXi 5/PIN analyzer offered by Röntgenanalytik Messtechnik GmbH has been especially optimized for the WEEE and RoHS analysis in plastics and solder. The large sample chamber allows non-destructive measurement of large plastic parts or PCB with various shapes.

Excitation conditions

Program Parameters

Fig. 1. Application example: printed circuit board.

Sample Preparation

The surface of the samples should be as much as possible even. Further preparation is not necessary as the small excited area reduce the geometric influence of the signal. The following Figure 2 shows the X-ray spectrum of polyethylene standard measured with Mo primary filter.

Fig. 2. Spectrum of the PE standard BCR-680.

Calibration

The using of special multi-mode non-linear calibration for thickness, background and matrix correction allows measuring of hazardous elements with high accuracy in PCB and different plastic materials with various shapes. The Figure 3 plotted a typical calibration curve for Cd

Fig. 3. Calibration curve for Cd in Plastic.

Analytical Features

Table 1 shows the analytical features of RoHS analysis of restricted elements Cd, Br, Hg and Pb in diverse plastic materials using X-ray MaXXi 5/PIN analyzer.

Limits of detection

Different filters optimized for measuring of Cd, Br, Pb and Hg allow to decrease the detection limits down to 20 ppm, that is one order of magnitude less than the RoHS limit for Cd and yet two order of magnitude less for other elements.

Accuracy of analysis

The high accuracy of ± 10 ppm can be achieved within an analysis time of 3 min for Br, Pb Hg and 5 min for Cd.

Reproducibility

For determination of reproducibility a 10 repeated measurements with a measuring time of 180 s have been realised on a few standard samples. Mean measured values and relative standard deviations are shown in the table 2.

Measurement report

Results of analysis can be summarized either in an easy measurement report or in a report file in Word format with a visualisation of measuring points and spectra imaging. The several report file templates can be generated and verified on the report template list.

Conclusion

The X-ray MaXXi 5/PIN analyzer allows rapid non-destructive direct measurement and quantification of regulated substances covered by environmental legislation, e.g. the RoHS and WEEE directives, in various plastic and powder materials and is well suited for screening and analysis of electrical instruments and components.