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Face-off: Destructive vs. Non-destructive Testing
December 31, 1969 |Estimated reading time: 3 minutes
Industry experts face off on destructive vs. non-destructive testing for RoHS compliance.
Advantages of Compliance Screening
Industries affected by the RoHS Directive have difficulty testing materials and products for compliance by relying solely on conventional lab methods. The number and diversity of components and materials makes lab-based compliance testing nearly impossible to perform in a reasonable time and at a reasonable cost. While looking for solutions, the industry also recognized the benefits of X-ray fluorescence (XRF) spectroscopy for material testing. XRF is a well-established analytical method that determines all elements of interest in a sample simultaneously, within a wide, dynamic concentration range, from limits of detection (mg/kg) to 100%. It can analyze all types of samples in 10-200 sec., with little or no sample preparation required. During analysis, the sample is not altered or destroyed, which is useful when repeated analyses are necessary, or in situations where the original sample must be preserved. Additionally, a handheld XRF analyzer allows the user to test objects, small or large, in real time, eliminating the need for destructive extraction of a small sample for lab analysis.
An XRF analyzer measures cadmium, mercury, and lead directly in a sample to ensure identification and elimination of non-RoHS-compliant components from the supply chain and production processes. As an elemental method, XRF measures only total element content of materials. For example, it cannot tell the difference between hexavalent or trivalent chromium, only how much total chromium is present. However, if the XRF measurement shows that the total chromium content of the sample is below the regulatory level, the object may be considered compliant, and no further testing is needed.
Screening with XRF can pinpoint potential compliance problems. By illuminating a 3-mm diameter area, the analyzer can isolate a leaded solder joint among many on a PCB. A quick scan of non-compliant cable insulation will reveal lead and bromine, as these additives often are present at percent concentrations. XRF screening lets users identify and separate components and materials into compliant, non-compliant, and those requiring further lab testing. Testing costs with a portable device are much less than multi-elemental lab analysis of a destructively extracted sample. On-site XRF analysis also yields results in real time, enabling more extensive testing. Ruggedness, portability, and tolerance to a range of samples positions handheld XRF as a first-pass screening tool to determine the need for more involved and costly confirmatory testing.
Stanislaw Piorek, Ph.D., principal research scientist, Thermo Scientific NITON Analyzers, may be contacted at stan.piorek@thermofisher.com.
Benefits of Destructive Testing
There has been much discussion over the most reliable way to test products to confirm compliance with the RoHS Directive. Many good techniques, both destructive and nondestructive, have emerged. However, despite the capabilities of non-destructive methods, destructive testing is the only way to ensure reliable analysis of materials.
There are three reasons why we maintain that destructive testing is the only way to certify, with confidence, that a product meets the maximum concentration value (MCV) requirements of RoHS. First, these concentrations are so low - 0.1% by weight for lead, mercury, chromium, polybrominated biphenyls (PBB), and polybrominated diphenyl ethers (PBDE); and 0.01% by weight for cadmium - that the accuracy of nondestructive techniques leaves an area of uncertainty that can only be resolved using destructive testing. Second, MCVs apply to homogeneous materials - parts that cannot be mechanically disjointed into single materials. Non-destructive techniques typically do not separate components into constituent parts, so the actual concentration of a restricted material might be under- or overstated. Third, most nondestructive methods cannot identify Cr+6, PBB, and PBDE. Normally, these methods report only total chromium and bromine. Testing may indicate the presence of a banned substance, but it does not provide conclusive evidence that this exists within the material.
The RoHS Directive also contains a number of exemptions, including deca-brominated flame retardants. Most nondestructive techniques cannot distinguish between exempt and restricted forms of PBDE. Therefore, results might wrongly report the presence of a restricted substance when the part is compliant. Destructive tests, on the other hand, can distinguish between exempt and restricted materials. Lack of a clear understanding of this issue can result in unnecessary costs.
Destructive testing for banned flame retardants provides accurate analysis of the specific forms of PBB and PBDE present. For example, gas chromatrography/mass spectroscopy (GC/MS) can distinguish between the exempt deca-PBDE and the other, banned forms. Therefore, destructive testing, in particular chemical testing, provides the most reliable way to confirm compliance with RoHS requirements, and a basis to assess compliance. It provides accurate extraction of the additives in electronic components so that they can be measured precisely, allowing a supplier to declare, with confidence, that products meet RoHS requirements.
David Kluk, director of technical development, NSL Analytical Services, may be contacted at dkluk@nslanalytical.com.