European Restriction of Hazardous Substances (RoHS) compliance has been in force since July 1. Many manufacturers who fall within the scope of the regulation have done what they believe is due diligence by collecting Certificates of Compliance or Declarations of Compliance from their suppliers. Some have even tested components. In spite of these efforts, some companies have found it necessary to voluntarily remove their products from the market, while still others are shipping product that is non-compliant, hoping they will not be exposed by enforcement organizations.

It is important for manufacturers to be 100 percent confident that their products are RoHS compliant, and just as important for them to understand the role of testing to deliver that confidence. Manufacturers should also grasp the pros and cons of different testing methods, know where testing fits in a compliance strategy, and be aware of real-life issues that producers face today in RoHS compliance.

Whether OEM design engineers perform the tests themselves, or contract with a lab to have them done, they need to understand their objectives and expected results. This is true not only with the performance specifications of a product, but also with regards to product compliance to hazardous substance requirements that have emerged recently. In addition to the European RoHS, hazardous substance regulations can now be found in all regions of the globe. Products must be compliant to remain on the market, and to reduce risk to the makers of the products.

Importance of testing

Enlarge this picture Chart 1. Flow chart of a compliance process that could help producers determine when analysis of components might be advisable. (from DTI, RoHS Regulations, Government Guidance Notes, Nov 2005, SI 2005, No. 2748, Annex D)

The reason for testing is that there is no other method to determine with certainty the hazardous substance content of a component or raw material. Most EU member states expect a producer to know that a product complies before putting the product on the market. Therefore, at some time in the manufacture of a product, each raw material and component should have been validated through testing to meet the limits on restricted substances set by the RoHS Directives.

A number of guidance documents have emerged that give similar information on what a producer should do to demonstrate compliance to global RoHS legislation. One example is the Department of Trade and Industry guidance from the UK. Shown in Chart 1 is the process the DTI recommends be followed to demonstrate due diligence in the attempt to comply with RoHS legislation.

In the process shown in Chart 1, a blue asterisk has been placed near process steps where testing or analysis is recommended. Analysis is recommended when the risk of non-compliance by a supplier or of a component is high. The analysis could be performed with non-destructive X-ray fluorescence (XRF) testing, or with destructive analytical-chemistry testing, or a combination of both.

Testing is the only method to determine the hazardous substance content of a component or raw material, other than knowing the exact formulation of the materials used. Formulation information is data that most companies do not have. Risk analysis can reduce the number of analyses required. If one can assess and assign risk to components and raw materials, then focus can be placed on only those components/materials that present the highest risk. This approach is suggested throughout the flow chart.

Choosing the test

Enlarge this picture Chart 2. Interpreting XRF Analysis Results and Determining Follow-On Lab-Based Analysis.

The decision about which test method to use is complex. It depends on the type of homogeneous material (HM) one is testing (plastic, metal, glass, ceramic, paint, packaging materials, or combinations of these that are still considered HMs). Test method selection also depends on accuracy, quality, cost, and speed. In many instances, design engineers can make this determination themselves, or they can work with a company that provides quality testing to make the decision with them. Because this decision quickly becomes technical , it is often recommended to rely on testing partners. However, one should still have a general understanding of testing and the trade-off of different test methods in order to make informed decisions in product design.

One can chose to use XRF testing or analytical lab testing to produce data related to compliance. Both of these test methodologies are detailed in the testing standard 111/54/CDV IEC 62321 [5/5/06, Ed. 1: Procedures for the determination of levels of six regulated substances (Lead, Mercury, Cadmium, Hexavalent Chromium, Polybrominated Biphenyls, Polybrominated Diphenyl Ethers) in electrotechnical products developed by the IEC TC 111 Working Group 3]. This testing standard is presently in the final voting phase, and was set to conclude Oct. 10, 2006. The standard is expected to be endorsed, and officially established before the end of the year. These methods each have their strengths and weaknesses, as noted in Table 1.

It is recommended to use a combination of both XRF screening, and analytical methods (when indicated) to understand compliance of a component or material. Note that there are different analytical methods for metals, plastics, and glasses. They all involve some sample preparation (grinding to small particle size), a chemical heat treatment with an acid, solvent, base, or other liquid, and an analysis of the chemical content using sophisticated tools such as atomic adsorption, gas chromatography/mass spectrometry, etc. XRF is a simple process of striking a sample with an energetic gamma-ray or X-ray, and measuring the emitted X-ray signal from the sample. This X-ray signal from the sample gives an analytical value of the magnitude of certain substances such as those specified in global RoHS legislation (Pb, Cd, Hg, Cr, and Br).

Types of samples

Enlarge this picture Table 1. Comparisons of testing methods.

The EU RoHS directives call for all HMs to be tested. There is a definition given for HM in the directive, but it is vague and difficult to interpret. Essentially, a product or component is disassembled with normal tools and laboratory procedures until a sample that is essentially uniform throughout is obtained. This is then considered an HM and can be tested. However, this does not always mean that one can achieve a “pure” HM. Many thin layers such as plated surfaces and paint can’t be removed easily and unambiguously, and, therefore, the final HM is tested as a composite. New standards are being developed to address this complexity. For now, it is wise to select a trusted testing partner to help make the right decision about what is considered a HM, and what is not. After the HMs are separated, they must be prepared for testing.

Samples need to be carefully prepared to achieve best quality results. Typically, a sample is cryogenically ground in a milling tool to a sample size of about 500 micrometers. The purpose of this is to expose a greater surface area to the chemical treatments to produce the highest hazardous-substance extraction possible. This has a direct impact on the quality of the quantitative measurement. In XRF, sample prep is not used for the most part. XRF measurement would benefit from sample preparation like milling, but because it is primarily used as a screening tool, no sample prep is recommended in most cases.

The accuracy of the measurement method is vital, and both XRF and analytical methods need to be checked against known standards called certified reference materials. Because XRF measurement of unusual surfaces may produce erroneous results, validation with analytical methods is recommended. An experienced company would produce a database of XRF and analytical testing of the same components and materials to have a complete understanding of the limits of the XRF tools for quantitative analysis. This effort is not to be taken lightly, as it will be crucial to the compliance effort. A company must do the level of R&D with XRF tools to have the confidence in the method to apply it properly.

Chart 1 indicates an approach to be used with XRF screening and subsequent analytical testing. In that chart, the green bars represent XRF measurements that can be interpreted as a “compliance pass” for RoHS limits set in the EU (<100 ppm for Cd; <1000 ppm for Pb, Hg, hexavalent-Cr, PBB, and PBDE). Note that Cd<50 ppm, Pb/Hg/Cr <700 ppm, and Br<300 ppm are considered compliance pass. These limits have been set to allow for the lack of accuracy typically associated with XRF screening. Only Cd, Pb, and Hg have a red bar that can be interpreted as a “compliance failure.” This is because if XRF measurement indicates a high level of either Cr or Br, this does not automatically imply that hexavalent-Cr, PBB, or PBDE are present, only that it might be present. A high value for Cr or Br implies that additional analytical testing should be considered to determine the presence of hexavalent-Cr, PBB, or PBDE.

Design engineers should be aware of some common testing errors. Some of those are listed below:

• Use of EN71 or other non-RoHS testing methods that are not acceptable.
• Not understanding that different colors require different HM testing to be performed for each color. Samples must follow definitions of HM.
• Failure to test for hexavalent-Cr and testing only for total Cr.
• Failure to test for PBB and PBDE, which is often neglected because it is a complicated test that requires expertise.
• Failure to identify or properly calibrate congeners in plastics testing, which is a common problem in PBDE tests.
• Testing that does not rigorously follow the homogeneous materials definition and philosophy. There must be separate tests for each HM.
• Date of test does not conform to company policy. Company documentation should be checked carefully.
• Performing XRF testing when analytical techniques were required. (hex-Cr, PBB, PBDE require analytical testing, and Cd in metals can’t be measured accurately with XRF).
• Failure to check the raw test data for test methods employed to determine if the testing and analysis was performed correctly.

Conclusion

A design engineer needs to rely on the test data that is provided to make an informed design decision. However, experience has shown that there are many areas of concern in the field today. The sidebar “Real Life Design Issues” lists areas of concern, and the questions and issues that should be addressed with the supply chain to develop quality designs with confidence related to RoHS requirements. The points should be carefully considered.

To ensure that their products are compliant, design engineers should remember why testing is important, what types of testing are available, as well as the strengths and weaknesses of each. And they should remain aware of typical pitfalls with which they may be confronted. Understanding the complexities of compliance can be challenging. Many manufacturers will find it helpful to form a relationship with a testing organization that can help identify and implement the optimal testing program that is tailored to the manufacturer’s specific needs.



For more information email: joel.pekay@us.ul.com

SIDEBAR: Real Life Design Issues

Bill of Materials:

• Make sure that BOMs are complete and include incidentals like glue, epoxy, screws, and fasteners.
• Make sure that RoHS compliance data is available for all components in the BOM.
• Establish a process for determining the source of a problem with a non-compliant component.

Supplier Approval:

• Make sure the process is fully documented and applied uniformly.
• Establish a procedure for dealing with a case of supplier non-compliance.

Acceptable Suppliers:

• Establish a documented process for monitoring supplier compliance and removing high-risk vendors from the supply chain.
• Establish a system for evaluating supplier declarations and test reports.

Using Test Laboratories:

• Make sure that the test lab is accredited and uses certified reference materials.
• Make sure that in-house experts can validate calibration methods used by the lab and that they have the capability of reading reports and interpreting data.