Energy Dispersive X-ray Spectrometer: Principle, Performance and Application in RoHS Testing

Abstract
This paper focuses on the LISUN EDX-2 Series Energy Dispersive X-ray Spectrometers, systematically expounding their detection principle based on the characteristic X-rays of elements, analyzing the performance differences of equipment through specific model parameter comparison, and taking RoHS testing as the core application scenario to illustrate their practical value in the screening of hazardous substances in electrical and electronic products. The research shows that, relying on the advantages of high resolution, multi-scenario adaptability and automatic operation, this series of x-ray spectrometers can realize elemental analysis with a content range from 2ppm to 99.99%, meeting diverse needs such as RoHS testing, alloy composition detection and coating thickness measurement, and providing reliable technical support for industrial quality control.

1. Introduction
With the global development of the electrical and electronic industry, the requirements for product material safety and environmental compliance have become increasingly strict. For example, the EU RoHS Directive restricts hazardous elements such as lead, mercury and cadmium, which has promoted the innovation of efficient elemental detection technologies. As a non-destructive testing equipment, the x-ray spectrometer has become a core tool for elemental analysis in the industrial field due to its advantages of no sample pretreatment, fast detection speed and high accuracy. The EDX-2 Series Energy Dispersive X-ray Spectrometers developed by LISUN Group cover multiple models including EDX-2A, EDX-2AC and EDX-2AB. They integrate three functions: RoHS testing, alloy analysis and coating thickness measurement, and can be widely used in fields such as electronic components, metal materials and plastic products. Their technical principles and performance are of great reference significance for industrial quality control.

2. Detection Principle of EDX-2 Series X-ray Spectrometers
The core detection logic of the EDX-2 Series Energy Dispersive X-ray Spectrometers is based on the differences in wavelength and intensity of characteristic X-rays of elements, and realizes qualitative and quantitative detection of elements through three steps: “excitation – detection – analysis”. The specific process is as follows:

2.1 Excitation of Characteristic X-rays
The equipment has a built-in X-ray tube. Under the working conditions of 50KV tube voltage and 600uA tube current (parameters can be set automatically), it emits high-energy primary X-rays to the sample to be tested. When the primary X-rays penetrate the surface layer of the sample, they interact with the inner-shell electrons of the atoms in the sample, knocking the inner-shell electrons out of the atomic orbit and making the atoms in an unstable excited state.

2.2 Generation and Detection of Characteristic X-rays
In order to return to a stable state, the outer-shell electrons of the atom will transition to the inner-shell empty orbit. During the transition process, an energy difference will be released, and this energy is radiated in the form of X-rays with a specific wavelength, which is called “characteristic X-rays of elements”. Different elements have different atomic numbers, and there are inherent differences in the energy level differences of electron orbits. Therefore, the wavelengths of the emitted characteristic X-rays are also unique – this is the core basis for the equipment to realize qualitative elemental analysis.

Subsequently, the characteristic X-rays are received by the detector (the EDX-2A uses a Si-pin detector, and models such as the EDX-2AC use a more high-precision SDD detector). The detector converts the X-ray signal into an electrical signal, which is then converted into recognizable spectral data by the signal processing system to form an elemental spectrum diagram with “wavelength – intensity” as the coordinate.

2.3 Quantitative Analysis of Elemental Content
Under the same detection conditions, the content of a certain element in the sample is positively correlated with the intensity of its characteristic X-rays – the higher the content, the more electrons transition, and the stronger the intensity of the emitted characteristic X-rays. By comparing the intensity of the elemental spectral lines of the sample to be tested with that of the standard sample with known concentration (such as the EU standard sample provided with the EDX-2 Series), and correcting the influencing factors such as matrix effect and background interference with software algorithms, the equipment finally calculates the accurate content of each element in the sample to be tested, realizing quantitative analysis. Its content analysis range can cover 2ppm to 99.99%, meeting the detection needs of trace and major elements.

3. Model Parameters and Performance Comparison of EDX-2 Series X-ray Spectrometers
The EDX-2 Series X-ray Spectrometers are designed with 5 core models for different application scenarios. There are differences in structural design, detector type and detection efficiency among various models. The specific parameter comparison is shown in the following table:

Specification Parameters	EDX-2A (Non-vacuum Desktop)	EDX-2AC (Vacuum Desktop)	EDX-2AB (Non-vacuum Desktop)	EDX-2ABC (Vacuum Desktop)	EDX-2T (Vacuum Desktop)
Equipment Weight	50Kg	55Kg	50Kg	55Kg	55Kg
Detection Time	200s	100s	200s	100s	100s
Sample Chamber Size	610×320×100mm (L×W×H)	Non-vacuum: 510×310×120mm   Vacuum: Ф100×70mm	610×320×100mm (L×W×H)	Non-vacuum: 510×310×120mm   Vacuum: Ф100×70mm	Non-vacuum: 510×310×120mm   Vacuum: Ф100×70mm
Testing Environment	Atmosphere	Vacuum	Atmosphere	Vacuum	Vacuum
Detector Type	Si-pin	SDD	Si-pin	SDD	SDD
Resolution	149eV	129eV	149eV	129eV	129eV
Output Tube Voltage/Current	50KV/600uA (Auto-set)	50KV/600uA (Auto-set)	50KV/600uA (Auto-set)	50KV/600uA (Auto-set)	50KV/600uA (Auto-set)
Types of Samples Tested	Solid, Liquid, Powder	Non-vacuum: Solid, Liquid, Powder   Vacuum: Solid	Solid, Liquid, Powder	Non-vacuum: Solid, Liquid, Powder   Vacuum: Solid	Non-vacuum: Solid, Liquid, Powder   Vacuum: Solid
Content Analysis Range	2ppm–99.99%	2ppm–99.99%	2ppm–99.99%	2ppm–99.99%	2ppm–99.99%
Core Applications	RoHS Testing	RoHS Testing, Coating Testing	RoHS Testing, Alloy Analysis	RoHS Testing, Alloy Analysis, Coating Testing	RoHS Testing, Alloy Analysis, Coating Testing
Element Range for Alloy Testing	Not Testable	16-S (Sulfur) to 92-U (Uranium)	16-S (Sulfur) to 92-U (Uranium)	16-S (Sulfur) to 92-U (Uranium)	11-Na (Sodium) to 92-U (Uranium)

It can be seen from the parameter comparison that the performance differences of the EDX-2 Series X-ray Spectrometers are mainly reflected in three aspects: first, vacuum environment adaptability. The EDX-2AC, EDX-2ABC and EDX-2T support vacuum testing, which can reduce the absorption of characteristic X-rays of light elements (such as sodium and magnesium) by air and expand the element range of alloy analysis. Second, detector accuracy. The resolution of the SDD detector (such as the EDX-2AC) is 129eV, which is better than that of the Si-pin detector (149eV). It can more accurately distinguish the elemental spectral lines with adjacent wavelengths and reduce detection errors. Third, function integration. The basic model EDX-2A only supports RoHS testing, while the EDX-2ABC and EDX-2T integrate alloy analysis and coating thickness measurement functions at the same time, adapting to more complex industrial scenarios.

4. Application of EDX-2 Series X-ray Spectrometers in RoHS Testing
4.1 RoHS Directive Requirements and Testing Standards
The RoHS Directive is an environmental protection standard for electrical and electronic products formulated by the EU. The current version is 2011/65/EU (RoHS 2.0). Compared with the original version (2002/95/EC), its scope of control has been expanded to medical devices and monitoring equipment, and manufacturers are required to keep technical documents and EC conformity declarations for at least 10 years. This directive limits the content of 6 hazardous substances, with specific requirements as follows: Mercury (Hg) ≤ 1000ppm, Hexavalent Chromium (CrVI) ≤ 1000ppm, Cadmium (Cd) ≤ 100ppm, Lead (Pb) ≤ 1000ppm, Polybrominated Biphenyls (PBBs) ≤ 1000ppm, Polybrominated Diphenyl Ethers (PBDEs) ≤ 1000ppm.
The corresponding standard in China is “Test Methods for Toxic and Hazardous Substances in Electronic Information Products” (SJ/T 11365-2006), which clearly designates the X-ray fluorescence spectrometry (XRF) as a rapid screening method for RoHS hazardous elements. The EDX-2 Series X-ray Spectrometers are developed based on this method and can directly meet the standard testing requirements.

4.2 Advantages of EDX-2 Series in RoHS Testing
As professional RoHS testing equipment, the EDX-2 Series X-ray Spectrometers have significant advantages in detection efficiency, operational convenience and safety:
• Rapid screening without pretreatment: The detection time of the EDX-2A is 200 seconds, and the vacuum models (such as the EDX-2AC) only take 100 seconds. There is no need for pretreatment such as digestion and dissolution of the sample, and samples in forms such as solid, liquid and powder (such as electronic component casings, plastic particles and solder paste) can be tested directly, which greatly shortens the detection cycle.
• High resolution and accuracy: The resolution of the SDD detector models (such as the EDX-2AC) reaches 129eV, which can accurately identify the characteristic X-rays of trace hazardous elements such as cadmium (Cd). Combined with the provided EU standard samples and calibration certificates, it ensures that the detection results meet international standards and avoids misjudgment.
• Visual operation and safety protection: The equipment is equipped with a high-definition camera and an in-chamber lighting system, allowing operators to check the sample testing position in real time and avoid detection errors caused by incorrect sample placement. At the same time, the equipment has power overcurrent and short-circuit protection functions, which conforms to industrial safety standards and reduces the risk of equipment damage.

4.3 Practical Testing Case
An electronics enterprise needed to conduct RoHS compliance screening on a batch of imported plastic components, and used the EDX-2A X-ray Spectrometer for testing:
• Sample preparation: The plastic components were cut into small pieces of 5cm×5cm and directly placed into the sample chamber (size 610×320×100mm) without other treatments;
• Parameter setting: The equipment automatically set the tube voltage to 50KV, the tube current to 600uA, and the detection time to 200 seconds;
• Detection results: The equipment generated an elemental spectrum diagram, showing that the lead (Pb) content in the sample was 850ppm and the cadmium (Cd) content was 30ppm, both lower than the RoHS limits, so it was judged to be compliant. At the same time, no other hazardous elements such as mercury and hexavalent chromium were detected in the spectral lines, and a RoHS test report was finally issued.

This case shows that the EDX-2 Series X-ray Spectrometers can quickly complete the RoHS screening of electronic components, provide a compliance basis for enterprises’ product exports to the EU, and avoid trade risks caused by excessive hazardous substances.

5. Other Core Applications of EDX-2 Series X-ray Spectrometers
In addition to RoHS testing, the EDX-2 Series X-ray Spectrometers also integrate alloy analysis and coating thickness measurement functions, expanding the application scenarios of the equipment:
5.1 Alloy Analysis
The EDX-2AB, EDX-2ABC and EDX-2T models support alloy analysis. Among them, the EDX-2T can detect all elements from 11-Na (Sodium) to 92-U (Uranium) in the periodic table, and is suitable for the composition detection of materials such as stainless steel, aluminum alloys and precious metals (gold, platinum). For example, in the jewelry industry, the EDX-2T can quickly determine the purity of gold jewelry (such as Au999, Au750) without damaging the sample; in the machinery manufacturing field, it can analyze the chromium and nickel content in stainless steel to judge whether the corrosion resistance of the material meets the design requirements.

5.2 Coating Thickness Measurement
The EDX-2AC, EDX-2ABC and EDX-2T models have the function of coating thickness measurement. They calculate the absolute value of the coating thickness by detecting the difference in the intensity of characteristic X-rays between the coating and the substrate material. For example, in the production of electronic connectors, the thickness of the nickel coating on the surface of the copper substrate (such as 5μm, 10μm) can be detected to ensure the conductivity and wear resistance of the coating; in the manufacturing of auto parts, the thickness of the galvanized layer can be monitored to evaluate the rust resistance of the parts.

6. Conclusions 
Based on the detection principle of characteristic X-rays of elements, the LISUN EDX-2 Series Energy Dispersive X-ray Spectrometers realize the multi-functional integration of RoHS testing, alloy analysis and coating thickness measurement. Their characteristics of high resolution, fast detection speed and wide sample adaptability make them important equipment for industrial quality control. From the parameter comparison, different models of equipment can meet the needs of different scenarios – the EDX-2A is suitable for basic RoHS screening, the EDX-2ABC is suitable for multi-scenario comprehensive testing, and the EDX-2T has advantages in light element analysis. Enterprises can choose the suitable model according to their own needs.

Tags：EDX-2A