RoHS Implementation Challenges

This article is part of the TechXchange: RoHS Design Issues

Most large, multinational corporations began RoHS compliance programs well before the publication of European Directive 2002/95/EC (RoHS) in January 2003. However, many small and medium sized companies have only recently begun to tackle the vast amount of work required to ensure their organizations are in compliance with RoHS/WEEE. There are a number of practical challenges cited for waiting ranging from the hope that legislation will be delayed to the financial need to have others do the basic materials science research required for conversion.

Table of Contents

• Key Challenges
• Product Conversion
• Assembly Process Conversion
• Due Diligence Documentation
• Product and Supply Chain Auditing
• Product Reliability
• Conclusions

Key Challenges

A number of workshops and conferences have provided a general outline of the work that must be done to bring products into compliance with the Directive. Websites such as the one sponsored by The British Ministry of Trade and Industry have provided valuable guidance. IEC working groups are working on chemical analysis methods for detecting the substances banned by RoHS.

Among the key challenges that are identified and being faced by organizations to achieve compliance are:

• Product Conversion including establishing Design for RoHS compliance guidelines and a review of each existing product Bill of Materials (BOM) for RoHS compliance.
• Establish and validate lead free assembly and inventory management processes.
• Gather, compile and store "Due Diligence" documentation in a data management system
• Set up an audit program to screen and chemically test incoming components
• Contemplate individual product reliability issues that can occur from materials and process changes.

Product Conversion

RoHS Compliance presents many product management and design challenges such as whether to bring an existing product into compliance or obsolete it, whether to make use of the currently granted exemptions or attempt to design products completely free of the six RoHS elements, and whether to incorporate other impending environmental initiatives such as halogen-free flame retardants. All of these choices significantly impact product cost, market timing and reliability.

At minimum, conversion of existing designs involves reviewing the Bill of Materials (BOM). For supplier designed purchased parts, the Approved Vendor List (AVL) must be reviewed and in many cases changed to reflect new RoHS compliant manufacturer's part numbers. This is not a trivial task given the vast number of individual part numbers and suppliers used by even a small electronics OEM. A reasonable estimate of component engineering time for one part might be 1.0 to 1.5 hours in order to review the AVL, investigate supplier's websites for RoHS compatible components, and then make changes in the document control and enterprise management systems. Given that a typical BOM might have between 50 and 100 supplier designed electronic components and that even a small company probably has at least 20 to 30 individual products, typical economics might resemble:

1.0 to 1.5 hours/product x $150/hour = $ 225/product
50-100 products/BOM = $16000
20-30 products x $16000 = $400,000

In addition to the off the shelf electronic components, each mechanical part drawing must be reviewed and, in some cases, changed to eliminate non-RoHS compliant materials. Consideration should be given to adding "Must be RoHS Compliant" callouts in drawings in addition to reviewing the materials of construction. Besides its role in solder and tin plating's, lead (Pb) is frequently used as an alloying element in metals to impart free machining or other desirable characteristics. Lead (Pb) has also found frequent usage in glass and ceramic chemistries to lower glass melting temperatures and improves other key properties. Fortunately, the issuance of exemptions has eased the engineering burden somewhat by allowing continued use of lead, cadmium and mercury in cases where no reliable technology yet exists to replace these elements.

Assembly Process Conversion

Fortunately, much of the fundamental assembly process research required to produce RoHS compliant assemblies has already been done and reported in forums such as the IPC/JEDEC lead free conferences. Despite this, there are still plenty of decisions for each company to make based on their individual product requirements. These include whether to go with a mainstream SAC alloy (Sn / Ag 3% / Cu 0.5%) or use a more specialty solder alloy for temperature or mechanicals reasons. Suitable methods must be adopted for keeping RoHS compliant and non-RoHS compliant inventories separated and accommodating both lead free and lead containing rework and field returns. An assessment must be done of the company's current contract manufacturer (CM) to determine if the CM has adequate equipment and experience with lead free processes and inventory handling. Given that all these preliminaries are in place, there is still the task of doing reevaluations on each converted product to establish reflow profiles, detect any product specific problems and generate functioning samples for product qualification and reliability testing.

Due Diligence Documentation

Most RoHS compliance directives favors the collection, evaluation and storage of extensive "due diligence" documentation from all component suppliers. This documentation typically should consist of a Certificate of Conformance to the RoHS Directive (CoC), a Materials Declaration that lists the percent composition, layer by layer, of all the substances in the component, and, if possible, chemical laboratory test data, which validates all the documentation. Some directives advise that a Certificate of Conformance should to be enough but European Union(E.U) advise that a CoC alone would not be treated as having done adequate "due diligence" should the product be challenged entering the E.U. European Union RoHS website provides guidance concerning due diligence, advising that there be a rational basis for determining whether a particular supplier's certification is trustworthy. In short, there is no, one size fits all prescription but it is clear that merely accepting a CoC from a supplier is probably not enough and that some combination of supplier evaluations, Materials Declarations, test data and the OEM's own auditing of this data is appropriate. Besides the purpose of supplier evaluation, the Materials Declaration turns out to be very helpful if XRF or chemical analysis is to be done since sample preparation schemes and instrument calibration can be a strong function of the non-RoHS materials in the sample.

While it is possible to extract some or all of this documentation from suppliers during the component conversion process mentioned previously, it requires considerably more effort than just discovering the suppliers RoHS or "Green" part number and placing that number in the AVL. Although some suppliers have readily offered all this information on their websites, in many cases, several emails or phone calls are required to convince suppliers to provide the Materials Declaration. There are a significant number who have yet to prepare Materials Declarations for their components. As mentioned previously, the data collection problems are compounded by the use of a large number of suppliers for a given part number. From a due diligence standpoint, data must be collected from each of the multiple suppliers listed for a given part number.

Product and Supply Chain Auditing

Auditing the supply chain through chemical testing is advised to part of a company's "due diligence" efforts as per EU RoHS directive. It is also advisable to prevent non-compliant components from being accidentally built into product. There are several current supply chain issues that make screening components prudent. Some component suppliers have not changed part numbers but merely converted to RoHS compliant parts after a particular date. The only way to prevent mixing their non compliant parts with compliant parts is by Date Code verification.

A typical chemical audit strategy of company is to incorporate the use of X-ray Fluorescence (XRF) equipment to screen components followed by further testing of suspected components using a variety of wet chemical instrument methods (ICP- AES, FTIR/GCMS, UV-VIS). XRF is commonly cited as the best means to quickly screen components. A number of desktop and handheld units are available. Casual use of tabletop or handheld XRFs can be useful in detecting gross amounts of RoHS substances in components such as the presence of bromine in plastics, high cadmium or lead levels in plastics. For example, to accurately detect 120 ppm Cd in a tin-silver-copper solder, it may be necessary to calibrate the XRF machine with a minimum of 3 NIST traceable standards that have 200 ppm Cd, 100 ppm Cd and 50 ppm Cd, respectively. Because of this, it is dangerous to assume that just because the XRF has not detected an element that the sample is RoHS compliant. XRF units can also give false positives as well. Table 1 shows an analysis of a cable with an XRF. The automated XRF program has detected high bromine, cadmium and mercury levels.

Table 1

Figure 1 shows that the automated XRF program has mistaken antimony (Sb) for cadmium (Cd). One of the antimony peaks occurs at the same spectral energy that the program was using to look for cadmium.

Figure 1. XRF can be mis-identified as Antimony (Sb) and Cadmium (Cd).

In Figure 2, the XRF may have mistaken thallium (Tl) for mercury (Hg).

Figure 2. The peaks of Thallium (Tl) and Mercury(Hg) are close together leading to confusion.

A more complex issue arises when a supplier of a passive component submitted Tin Lead plated component for Chemical Analysis and when they found that the lead concentration is below 1000 ppm, they advertise the component as RoHS Compliant. By EU RoHS directive, the component is Non RoHS Compliant because lead concentration in termination plating is 15% and not 1000 ppm. This can be easily verified by the Scanning Electronic Microscope Energy Dispersive X-Rays (SEM-EDX) beams. In this the part is compliant only when all its constituents are complaint called HOMOGENEOUS material.

Still there are many challenges that remain with the sampling practices particularly with attempting to analyze individual homogeneous layers of component. Many electronic components are smaller than the minimum sample size for wet chemical methods so multiple components must be used to make up one sample for analysis. Adding to these difficulties is the requirement that each "homogeneous constituent" layer (plating layers, sub component constructions, etc) of a component must meet the RoHS substance maximum limits. In many cases, economical means have not been found to analyze individual layers of tiny electronic components.

Figure 3 and figure 4 show examples of electronic components that have been cross-sectioned and the homogeneous constituent layers have been identified.

Figure 3. This is an example of a cross section of a homogenous constituent layer in a 0402 capacitor.

Figure 4. This is an example of a cross section of a homogenous constituent layer in a 0402 inductor.

For the parts shown in Figures 3 and 4, it may take as many as 1200 of these 0402 components to make up constitute the 2 grams required for standard ICP-AES chemical analysis for lead, cadmium, mercury. There are methods such as Laser Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) that will permit parts per million chemical analyses of the individual layers of one component such as those shown in Figures 3 and 4 but these methods can cost as much as $600 per layer or several thousand dollars per component. Clearly the environmental impact of RoHS elements in some of these components does not justify such costs and it is also hoped that future enforcement actions will not require it either.

To proceed with more accepted method of ICP-AES testing, it would be required to dissolve the component into a liquid that can be injected into the instrument (Fig. 5).

Figure 5. This shows the sample preparation process for chemical analysis of an electronic component.

Product Reliability

One last area to consider is product reliability verification. Companies have to conduct qualification testing after any major process change, several features of lead free soldering makes this an imperative. The SAC alloys used to replace tin-lead alloys have different solder fatigue properties and while most types of SMT solder joints appear at least as reliable with lead free alloys. In addition, the higher reflow temperatures required by SAC alloy subject all the materials in the assembly to increasing thermal stresses making issues of moisture sensitivity worse. Many component packages have been redesigned to accommodate these higher temperatures. Standard printed circuit boards are no longer suitable for many designs because of the higher reflow temperatures. All of these factors make extensive product requalification a necessary part of converting products for RoHS compliance.

Conclusions

Neither the RoHS Directive nor government guidance documents address precisely what a company must do to ensure RoHS compliance other than be sure that the levels of the six RoHS elements are below the prescribed limits. Most believe that simply obtaining Certificates of Compliance from suppliers is probably not adequate but there is considerable flexibility in what constitutes "due diligence" beyond this. This challenges list is lengthy and there are many gray issues yet to be resolved. Most companies have found that conversion takes several years from the time management decides to respond until the final qualification testing is complete.

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