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RoHS Testing: Lead-free Is Not Trouble-free
December 31, 1969 |Estimated reading time: 8 minutes
PCB suppliers have focused on removing lead from their products to conform to RoHS requirements. But the attention on lead has caused some suppliers to overlook other important issues. This article highlights what to watch for when evaluating your RoHS testing program.
By Carm D’Agostino, Adrian de Krom, and David Kluk
he electronics industry has been scrambling to comply with the RoHS Directive, which took effect last month. With similar legislation being considered in China, California, and 21 other U.S. states and Canadian provinces, the issue takes on global implications (Figure 1). The advent of the RoHS Directive has led to a great deal of confusion in the industry over what is required. This article details seven issues that you should be aware of when establishing a RoHS-testing strategy.
Figure 1. Yellow areas denote active or pending RoHS legislation.
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It’s Not Just About Lead
Visit trade shows or read magazine articles, and everyone is touting lead-free in their circuit board designs. At issue are solder joints, which traditionally have been tin/lead. A great deal of work has been done in recent years to replace tin/lead solders with tin/silver/copper (SAC) solders, while maintaining circuit performance and board life. While designers have been largely successful in eliminating lead, they have ignored an equally important issue in PCB design. Most reinforcing materials in PCBs contain brominated fire retardants (PBB and PBDE). Thus, while circuit boards may be free of lead, they may be rejected because of their PBB and PBDE content.
Test Materials, Not Circuits
PCB designers are familiar with the use of electrical testing to verify circuit integrity. However, RoHS testing is all about the materials. As a result, most manufacturers of electronic components are not equipped to perform the materials testing needed to detect the presence of restricted substances. Only a reliable materials test lab can do this. It does a supplier little if the circuit passes but the board is rejected because it fails the materials test.
X-rays Are Only Skin Deep
Manufacturers of bench-top and handheld X-ray fluorescence (XRF) equipment are gaining a lot of publicity for claiming their systems can detect restricted materials without destructive testing. While XRF can play a vital role for RoHS-compliance testing, its main strength is as a screening tool to identify high concentrations of restricted substances that are significantly above regulatory limits. It is helpful in areas requiring the ability to quickly determine if a particular substance is present, rather than where precise information concerning concentrations is needed.
Figure 2. Dynamic reaction cell in an ICP mass spectrometer reduces interferences inherent in the process. This eliminates false positives and allows the detection of elements present at extremely low levels.
Caution must be taken when relying on the accuracy of values generated using XRF systems. Measurement errors of ±30% and up to ±50% in electronic components are not uncommon when using XRF systems. These large margins of error are due in part to depth of penetration, beam size, spectral interference, matrix interference, lack of comparative standards, and the availability of sufficient uniform surface area. Alternative testing methods are required to make accurate determinations (Figure 2). Table 1 outlines available test methods to assess the presence of restricted materials.
Table 1 Test methods used to assess the presence of restricted materials.
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What Do Test Results Mean?
The RoHS Directive restricts the use of the following hazardous substances: lead, cadmium, hexavalent chromium, mercury, PBD, and PBDE. These substances are found in several forms in a variety of components. An example is lead used to reduce the melting point of solder for enhanced processability. Lead can also be used as a heat stabilizer in vinyl insulating material for electrical cords, as can cadmium. Hexavalent chromium is commonly used as a self-healing conversion coating to prevent corrosion. Chromium can also be found in pigments used for colorants; brominated compounds are commonly used as flame-retardants in electronic devices.
Screening techniques such as XRF cannot assess true compliance status. Positive identification of chromium and bromine above threshold limits does not indicate lack of compliance. But it is important to understand the form of these substances, and sophisticated analytical techniques are required to make an accurate assessment.
The RoHS Directive also contains a number of exemptions, including lead in glass, up to 4% lead in copper alloys, and up to 0.35% lead in steel and deca-brominated flame-retardants. Understanding these exemptions and identifying the materials associated with them is critical to determine true compliance. Lack of a clear understanding of these issues can result in unnecessary costs.
Extraction Efficiency
Accurate quantification of PBB and PBDE flame-retardants depends not only on having the correct instrument, but also on the efficiency of extracting the material from the component under test. Selecting the proper solvent is critical to ensure the complete removal of all PBB and PBDE for analytical testing.
Accurate Procedures and Auditing
A reliable materials-test lab is critical to gaining accurate analysis of electronic components. Ideally, to ensure compliance, the test lab should use the same procedures as the importing countries. If possible, regular auditing should also be done to ensure that the lab you use continues to follow accepted practices.
In the U.S., various government agencies and industry leaders have shown interest in devising a rational approach to RoHS testing that will govern how testing is done. The approach will include in-plant process audits, materials declarations, and analytical testing for validation on a regular basis. To ensure conformance, the test lab should be willing to provide a full compliance statement along with test results. This will offer the documentation necessary to prove compliance.
The U.K.’s Department of Trade & Industry (DTI) has developed a recommended guideline for RoHS compliance. Under this guideline, producers will self-certify that their products comply with the RoHS Directive. However, this certification should be supported by accurate test data and reported in a standard format suitable for auditing. Producers are also encouraged to perform periodic analyses to check the accuracy of test data. To ensure traceability, they should keep clear, detailed records. Finally, they should take all reasonable steps to ensure compliance, and be able to demonstrate these steps.
One clear requirement is a uniform materials-declaration standard to ensure compliance and reduce costs. To provide uniformity in the industry, the DTI has proposed the use of IPC-1752, which recommends the following levels of declaration:
• Class 1 - RoHS reporting at homogeneous level in yes/no format;
• Class 2 - RoHS reporting at homogeneous level in yes/no format, plus manufacturing information;
• Class 3-RoHS reporting at homogeneous levels in yes/no format, Joint Industry Guide (JIG) level A & B at the part level, and other customer-specific substances at the part level;
• Class 4 - Same as Class 3, with the addition of manufacturing information;
• Class 5 - RoHS reporting at homogeneous levels in yes/no format and JIG level A & B at the homogeneous-material level, and other customer-specific substances at the homogeneous level;
• Class 6 - Same as Class 5, with the addition of manufacturing information.
IPC-1752 outlines an electronic data-reporting model with a standard form for data input. It also recommends XML schemes for automated data extraction and exchange. The U.S. has issued TC 111, with the following Proposed Hierarchy of Materials Declaration Standards:
• IEC 3/750/DPAS (draft) - Defines high-level requirements for materials declarations.
• JIG defines specifics of what must be reported, such as criteria established for reportable substances and lists of reportable substances and thresholds.
• IPC-1751/1752 (draft).
Many other standards-setting organizations are contributing to the standardization of material-content data reporting, including Rosetta Net; 2A10 and 2A13 PIPs; iNEMI, Material Declaration Project; Material Composition Data Exchange Project; VEI, NEDA, and JEITA.
Homogenization Is for Milk
The RoHS Directive defines the maximum amount of a restricted substance that will be tolerated in each homogeneous material. The term homogeneous is not defined in the RoHS Directive, in the related WEEE Directive, or even in the “Guide to the implementation of directives based on the new approach and the global approach,” commonly called the Blue Book. The term, which first appeared in a Commission document in December 2003, states: “Homogeneous material means a unit that cannot be mechanically disjoined into single materials.” A homogeneous material can be understood as being of uniform composition throughout (Figure 3). Examples include individual types of plastics, ceramics, glass, metals, alloys, paperboard, resins, and coatings. The term mechanically disjointed means that the materials can, in principle, be separated mechanically by unscrewing, cutting, crushing, grinding, or abrading.
Figure 3. Each part of a non-homogenous component, such as a computer chip, is considered to be a homogenous material because each can be, in theory, separated for individual testing.
Some test facilities do not understand the implications of this guidance, and are making the mistake of homogenizing circuit boards and devices. That is, they are treating them as homogeneous materials, rather than as an assembly of parts that can be mechanically disjointed. This practice can dilute the amount of restricted material that may be present, leading to under reporting of hazardous material levels and potential rejection of the device by the importing country.
Conclusion
The intent of the RoHS Directive is that each component of an assembly, including coatings, platings, solder, and insulation be tested separately. Separating an assembly into its component parts and testing each can be a tedious, time-consuming job. But it is worth the effort to ensure acceptance of the imported device.
Carm D’Agostino, RoHS manager, NSL Analytical Service Inc., may be contacted at (216) 503-5016; e-mail: cdagostino@nslanalytical.com. Adrian de Krom, manager, Polymer Analytical Group, NSL Analytical Service Inc., may be contacted at (216) 447-8813; e-mail: adekrom@nslanalytical.com. David Kluk, technical manager, NSL Analytical Service Inc., may be contacted at (216) 503-5015; e-mail: dkluk@nslanalytical.com.