Restriction of Hazardous Substances (RoHS) Background
RoHS (Restriction of Hazardous Substances) began its life as a directive in the European Union (EU) in the early 2000s and was revised into a new directive in 2011. The purpose of the directive is to provide for end of life suitability for disposal of electronic components specifically (with some notable exceptions specified in the directive). The directive specifically restricts the use of the following materials to a maximum level also specified:
- Lead (Pb) to 0.1% by weight
- Hexavalent Chromium (Cr-6) to 0.1% by weight
- Mercury (Hg) to 0.1% by weight
- Cadmium (Cd) to 0.01% by weight
- PBB (polybrominated biphenyls) to 0.1% by weight
- PBDE (polybrominated diphenyl ethers) to 0.1% by weight
In addition to the above listed restricted substances, the EU directive will phase in the following phthalate components (plasticizers) starting in July 2019:
- DEHP (Bis (2-ethylhexyl) Phthalate) to 0.1% by weight
- BBP (Butyl Benzyl Phthalate) to 0.1% by weight
- DBP (Dibutyl Phthalate) to 0.1% by weight
- DIBP (Diisobutyl Phthalate) to 0.1% by weight
In addition to the RoHS components above, RTI offers testing for additional phthalates to comply with directives provided under the CPSIA (Consumer Products Safety Information Act):
- DINP (diisononyl phthalate)
- DIDP (diisodecyl phthalate)
- DnOP (di-n-octyl phthalate)
The EU RoHS directive thereby puts the burden on the manufacturer, distributor, and retailer of electronic and electric goods into and within the EU to be RoHS compliant. In addition to the EU, several other countries have also adopted RoHS trade legislation (including China and Korea) that have patterned their restricted materials and levels after the EU directive. The State of California also has RoHS legislation that specifically addresses electronic goods with video screens larger than a certain size. The answer to specific state legislation, however, was the introduction of the Environmental Design of Electrical Equipment Act (EDEE) in 2009 that was intended to be an amendment to TSCA of 1976 for implementation as a unified regulation throughout all 50 states. As of this writing in 2016, this bill has yet to materialize, however many US manufacturers are readying for this regulation as they are often also exporting into RoHS regions. The good news, however for testing and compliance is that there are many similarities in the EU directive and the non-EU RoHS legislation, including the substances restricted and levels restricted to.
Ultimately compliance with this legislation can be relatively simple if proper documentation is maintained from “beginning of life” of electronic materials. Much of RoHS registration relies on declaration of conformance for the raw materials and components used in the manufacture and assembly of electronics that can be carried forward through a final assembly or product.
Having complete documentation of the uses of restricted materials in all components would make testing of the end product likely unnecessary. Unfortunately in the global supply chain and usage of non-traceable or non-RoHS compliant raw materials, testing often becomes necessary to meet the RoHS requirements.
RoHS Testing Options
So now that we have a finished product that at least some level of testing is required for RoHS compliance, we can take a look at some of the options for testing relative to the regulations. If we could just take that LCD screen or cell phone, throw it in a grinder for homogenization and particle size reduction, sample preparation and analysis is fairly straightforward for the target restricted substances. The trick however is applying the interpretation of the “homogeneous material” definition of the legislation to a final assembly. And these level restrictions have to be applied to each homogeneous material component of the end product. Both the EU and US have defined “homogeneous material” as the component in its smallest form that cannot be further mechanically separated.
So by definition, an electronic product can have tens if not hundreds of pieces for which the regulated levels would apply, including the screens, batteries, circuit boards, components on the circuit boards and so forth. Of course the components that do have certificate of conformance along with the supply can preclude testing.
RoHS Compliance Procedure
The essential procedure for those seeking RoHS compliance or registration on their end electronic product is to first identify whether the end product (or part of the product) falls under an exemption for a particular parameter based on its designated use. This will vary between which RoHS standard is to be applied, but ultimately is the first step to determining whether the path to compliance is necessary. The exemptions are clearly stated in the referring standards. Second in the procedure is to have a thorough understanding of the components that make up the final product. As a manufacturer, this information is readily available, however, as a distributor this will often require cooperation with the manufacturer to understanding the makeup. Next in the process is documentation gathering on the components that make up the product. Ultimately this can be the most tedious part of the process but again will be beneficial in cost and headache for the final step. The gap assessment is next to identify the components that are essentially undocumented as far as conformance is concerned. The results of the gap assessment will then dictate which components of the product need to be tested per the RoHS standard.
The quantitative testing specified for the full list of RoHS materials does require multiple methods for analysis to meet required quantitation limits to be under the maximum levels specified. Elemental screening techniques such as XRF (X-ray Fluorescence) are allowed that are capable of meeting the detection limit requirements, however this technique will not speciate the chromium between hexavalent and trivalent chromium and will also not provide compound information regarding identified bromine. In addition, targeted XRF analysis on small components can also become just as costly as full quantitative analysis with the preferred methods.
RoHS Analysis Preparation
Preparing for analysis then requires the user and laboratory to identify and segregate the homogeneous materials in the product. Often it may be necessary to use more than one (of the same) product to provide enough mass of the homogeneous material to properly characterize its content. The homogeneous materials are then segregated and need to be homogenized by “particle size reduction” techniques to ready for analytical preparation. This can be as simple as brute force pulverizing, smashing, milling, drilling, etc. to reduce the particle size for proper statistical sampling of the mass.
As all of the quantitative methods of analysis (besides the screening method) require the sample to be analyzed in liquid form, the preparatory methods will then “extract” the target analyte from the sampled mass. The sampled mass is then treated with a liquid for extraction depending on the method, and the resulting extract filtered of the remaining sampled mass suspended solids. The extract may then be further treated for analysis depending on the analytical method requirements.
For the metallic analytes (Cd, Pb, and Hg), the extraction liquid is typically a concentrated acid. The Hex Cr analyte requires a different liquid as to not alter the oxidation state of the extracted chromium (this is typically an alkaline aqueous solution). For the brominated compounds (PBB and PBDE), the extraction liquid is typically a halogenated solvent that will also be capable of dissolving plastic materials in the sampled mass.
For quantitative determination, the metals will involve spectrographic techniques to measure the quantity of the analyte in the extraction liquid. For Cd and Pb, the spectrographic technique can be atomic absorption, emission, or mass spectroscopy. (AA, ICP-OES, ICP-MS). Hg determination will typically involve a cold vapor atomic absorption (CVAA) or Flow Injection (FIA) analysis method. The Hex Cr determination will typically involve a spectrophotometric analysis (UV-Vis) after reaction with diphenylcarbazide or an ion chromatographic (IC) analysis. The brominated compounds determination will involve chromatographic separation (either gas chromatography or liquid chromatography) coupled with mass spectroscopy detection. It must be noted that since brominated materials are typically not industrially prevalent, screening for the brominated compounds is often suggested prior to full quantitative analysis, as the quantitative methods can be costly. The obvious exception is when the homogeneous material is known to contain fire retardants.
RoHS Compliance Analysis Completion
As the analysis completes for the undocumented homogeneous materials, the test reports then become the “declaration of conformance” for those materials to complete the gap assessment. All declarations of conformance then become the primary submittal materials for RoHS registration. Where non-compliance has been identified in a homogeneous material, it is possible that this material is exempt based upon its use as specified in the particular RoHS standard.