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Sample Preparation Specification for ROHS Tester: Pre processing Steps to Ensure Accurate Test Results
Date: 2025-11-22Read: 0
ROHS testerThe detection accuracy largely depends on the quality of sample pretreatment. Standardized sample preparation can effectively reduce interference factors and ensure that the test results truly reflect the content of harmful substances in the material.
1、 General principles: representativeness and uniformity
Samples should be selected from key parts of the product to be tested to avoid misjudgment caused by local differences. For example, when detecting harmful substances in electronic products, priority should be given to high-risk areas such as soldering points (including solder), plastic casings (which may contain flame retardants), circuit boards (including heavy metal coatings), etc; For bulk products, random samples (usually 3-5 samples) need to be taken from different batches, and the average value should be taken to improve representativeness.
2、 Pre treatment specifications for different materials
Metallic materials:
Surface treatment: Remove oxide layers (such as rust, copper green), oil stains, or electroplating layers (if the electroplating layer may contain cadmium/lead, it is necessary to clarify whether the detection target is the substrate or the coating). You can use sandpaper (such as 200-400 grit) to gently polish to a metallic luster, or wipe the surface with organic solvents (such as alcohol).
Block shaped sample: If the size is too large, it needs to be cut into small pieces (thickness<1cm) to ensure a flat test surface; Powdered metals (such as alloy powder) need to be sieved (e.g. 200 mesh) and mixed evenly to avoid particle size differences affecting X-ray penetration.
Plastic and polymer materials:
Coating treatment: If the plastic shell is painted, electroplated, or coated, it needs to be sanded with sandpaper until the substrate is exposed (to avoid interference from additives in the coating during testing). For example, when detecting brominated flame retardants (PBDEs) in plastics, the clear varnish layer on the surface needs to be removed.
Homogenization treatment: The block shaped plastic needs to be cut into thin slices (thickness<5mm) or pressed into a cake shape (using a tablet press with a pressure of about 10-20 tons to ensure consistent density); Irregular samples can be ground into powder (particle size<100 mesh), mixed and taken into a sample cup in an appropriate amount.
Electronic components and circuit boards:
Disassembly and Separation: Prioritize separating different materials (such as separating plastic shells, metal pins, circuit board substrates) and testing them separately. For example, the solder of the circuit board needs to be sampled separately to avoid confusion with the glass fibers in the substrate.
Surface cleaning: Wipe the surface of the component with anhydrous ethanol to remove fingerprints, dust, and other pollutants; For small components such as resistors and capacitors, they can be tested as a whole, but their material type needs to be recorded (e.g. ceramic capacitors may not contain bromine, while plastic packaging may contain flame retardants).
Liquid and powder samples:
Liquids (such as cleaning agents, electrolytes): need to be sealed in transparent containers to avoid volatilization; If heavy metals (such as hexavalent chromium) are detected, they need to be stabilized with acid (such as nitric acid) to prevent changes in ion form.
Powder (such as solder paste, coating): Sift (such as 100-200 mesh) to remove large particles, mix evenly, take an appropriate amount (about 0.5-1g) and put it into a sample cup, scrape the surface flat to ensure consistency in the detection area.
3、 Special precautions
Avoid contamination: All tools (such as sandpaper, tweezers) should be used exclusively to avoid cross contamination (such as not cleaning the tools after testing lead samples, and retesting lead-free samples can lead to misjudgment).
Sample size and morphology: XRF detection usually requires a flat sample surface and sufficient thickness (X-ray penetration depth of about a few micrometers to millimeters). If the sample is too thin (such as thin film plastic), multiple layers need to be stacked or a dedicated support frame needs to be used; ICP detection requires liquid samples (which need to be converted into solutions through digestion).
Status recording: Record the original state of the sample (such as color, surface treatment process) in order to eliminate process interference when analyzing the test results (such as the possibility of cadmium in the plating layer but not in the substrate).
Standardized sample preparation is the first hurdle in ROHS testing. Only by ensuring that the samples are representative, uniform, and free of contamination can a reliable basis be provided for subsequent testing, and accurate results reflecting the harmful substance content of the product can be obtained to assist enterprises in compliant production.