The ROHSXRF analyzer is based on X-ray fluorescence spectroscopy (XRF) technology, which achieves non-destructive and rapid detection by exciting the characteristic X-ray fluorescence of elements in the sample. Its core principles and key technologies are as follows:
1、 Excitation and fluorescence emission mechanism
Primary X-ray excitation
The built-in X-ray tube of the instrument (such as Rh target) generates high-energy primary X-rays, which penetrate the surface of the sample and interact with the inner layer electrons of the atoms. When the X-ray energy exceeds the electron binding energy, the inner layer electrons (such as the K layer) are ejected to form holes, and the atoms enter an excited state.
Characteristic fluorescence emission
Excited state atoms are unstable, and outer electrons (such as the L layer) transition to fill holes, releasing energy differences to form characteristic X-ray fluorescence. For example, the K α fluorescence energy of lead (Pb) is 74.97 keV, and that of cadmium (Cd) is 23.17 keV. The fluorescence energies of different elements have different properties, forming an "element fingerprint".
2、 Fluorescence signal detection and analysis
Energy dispersive X-ray (EDXRF) detection
The fluorescence energy is directly measured using a silicon drift detector (SDD), and the signal is converted into an energy spectrum using a multi-channel analyzer (MCA). The horizontal axis represents energy (keV), the vertical axis represents count rate, the peak position corresponds to the type of element, and the peak area is positively correlated with the content.
Wavelength dispersive X-ray (WDXRF) detection
Fluorescence is separated by wavelength using a crystal spectrometer, and the detector scans the spectrum point by point. WDXRF has higher resolution, but requires mechanical rotation of components, resulting in slower analysis speed.
3、 Quantitative analysis techniques
Basic Parameter Method (FPM)
Based on theoretical models to calculate fluorescence intensity, combined with sample matrix effects (such as absorption enhancement effects) to correct the results, it is suitable for complex matrix samples.
Empirical coefficient method
Establish a calibration curve using standard samples and determine element content through regression analysis. For example, when detecting lead content in a circuit board, it is necessary to select a standard sample that matches the sample matrix (such as epoxy resin).
No standard sample analysis technique
The instrument manufacturer stores standard sample data in advance, and users can calibrate instrument drift by referring to the sample to achieve rapid screening. However, this method has limited accuracy for light elements such as chlorine and bromine.
4、 Technical advantages and application scenarios
Core strengths
Non destructive testing: No need to destroy the sample, suitable for screening finished products.
Quick analysis: A single detection only takes seconds to minutes.
Multi element synchronization: It can simultaneously detect elements such as lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls, etc., which are restricted by the RoHS directive.
Typical Applications
Electronic manufacturing: detecting harmful substances in circuit boards and connectors.
Toy industry: Screening for heavy metals (such as antimony and arsenic) in children's toys.
Environmental monitoring: Analyze heavy metal pollution in soil and water bodies.
5、 Limitations and improvement directions
Detection limit and substrate interference
The detection limit for light elements such as chlorine and bromine is relatively high, and vacuum mode or helium blowing should be used to reduce air absorption. Complex matrix samples require laser ablation (LA-ICP-MS) to improve accuracy.
Hexavalent chromium testing challenge
XRF cannot distinguish the valence state of chromium and requires supplementary analysis through chemical titration or X-ray absorption near edge structure (XANES) techniques.
The ROHSXRF analyzer provides an efficient and reliable technical means for environmental compliance testing by accurately exciting and detecting elemental characteristic fluorescence, and is a key tool for the green transformation of the electronics industry.