Risks, considerations and impacts, plus several BoM analysis case studies.

The European Union’s Restriction of Hazardous Substances Directive was adopted in Febuary 2003 and took effect in July 2006. Exemption categories defined in the Waste Electrical and Electronic Equipment (WEEE) Directive under Annex IA and IB that also apply to the RoHS Directive include medical devices (Category 8) and monitoring and control instruments (Category 9). The EU recognized these products are typically manufactured in small numbers and have a long product life. Products within these categories are often used in critical applications where a failure may have a significant impact.

Long-term effects of Pb-free solder and the associated new materials used in these products are not fully known. In the ERA Technology Final Report, researchers stated it is not yet possible, on the basis of accelerated test data, to predict accurately the field life of equipment used for more than 10 years in a hostile environment. This is because comparable field data for products made with Pb-free solder are not yet available. Based on the concern for potential manufacturing defects, thermal fatigue, tin whiskers, vibration failures and corrosion, the EU established a temporary moratorium for Category 8 and 9 products. Working with the European Commission, ERA Technology recommended these products remain exempt from the RoHS Directive until 2012 or 2020, depending on specific product categories and applications (Table 1).¹ This six-to-14-year window provides medical OEMs time to redesign products, undertake more reliability testing and obtain appropriate approvals.² A number of additional countries are considering or deploying environmental regulations similar to RoHS and WEEE.


With medical products exempt from the EU directives, medical companies are contemplating waiting versus compliance. Multiple factors should be taken into consideration.

• Environmental laws – Medical products are still exempt from RoHS compliance; however, the official China Catalogue is not yet released, so medical product status there is unknown. Other countries developing or enacting environmental laws include Japan, South Korea and Australia. The process of medical product design, validation, clinicals and release is long; OEMs should keep this in mind.
  
  
• Marketing – Consumers are becoming more aware of the environmental impact and “greening” of electronics. Some use “green” as a factor in product selection. Some companies reportedly have obtained a five to 10% market share increase by selling green products. On the other side, one major consumer electronics provider received negative press from Greenpeace for the material content in its multimedia and Internet-enabled mobile phone. (Greenpeace felt the product did not do enough to reduce environmental impact.³) Medical companies should monitor the market to determine the significance of a product’s environmental friendliness and its impact on customer decisions.
  
  
• Material supply – Multiple material considerations need to be taken into account:

Component obsolescence. As components have moved to compliance, vendor capacity and/or component margins have motivated suppliers to obsolete certain components. “Many companies producing COTS parts have discontinued noncompliant versions now that they’re producing RoHS-compliant parts.”⁴ Material obsolescence needs to be monitored on a regular basis to ensure product continuity is not interrupted. For new product developments, medical OEMs should consider the impact of SnPb component obsolescence. Medical OEMs need to weigh the cost of product redesign and validation in the event of obsolete material versus establishing the necessary infrastructure within their organization to support environmental compliance.

Component availability. In Benchmark’s experience, many vendors have shifted to RoHS-compliant components and the industry has stabilized; we see typical fluctuations in RoHS component availability based on industry demands. However, for SnPb components, especially through-hole components, availability and cost are changing. Vendors are reducing or eliminating some lower-margin through-hole components and increasing the price of SnPb components, in some cases by 30%. “Those parts are still being produced, but their prices are likely to increase, since they will be produced in smaller quantities as the high-volume commercial industry shifts to RoHS-compliant parts.”⁵ This will impact both price and availability, potentially driving some companies to brokers for component supply, which leads to other associated risks.

Component compatibility. Many SnPb components have been converted to RoHS compliant by switching the component lead finish to a non-lead material. These components are backwards compatible: They can be soldered with SnPb or Pb-free solders. There is, in some cases, potential for new Pb-finishes to develop tin whiskers. In addition, some component manufacturers will change the component lead finish for compliance, but the component’s maximum case temperature may not be able to handle the higher temperatures of Pb-free soldering.

The greatest risk for manufacturing process incompatibility is with BGA packages. Suppliers are converting BGAs from SnPb solder balls to SAC alloy spheres with a silver content of 1 to 4%. The temperature required to solder the SAC alloy is typically 30°C higher than that of SnPb (Table 2). SnPb soldering at 208° to 218°C is too low for Pb-free, which requires 240° to 248°C. Using a hybrid process of 225° to 235°C, the temperature becomes too hot for some SnPb package case temperatures and too low for Pb-free solder reflow. The hybrid process may be used for prototypes, but is not recommended for production product. OEMs will find this is an industry-recognized issue.


If the OEM chooses to keep its products SnPb, it needs to put processes in place to mitigate risks within the products. Component monitoring and BoM scrubs should be an ongoing activity for the materials team. Obsolescence analysis of SnPb components should help identify when a component is going end-of-life (EOL). Leveraging a component engineering team, the OEM can select second sources or alternates, purchase last-time buys, or redesign to eliminate obsolete materials, in addition to potentially costing down the product. Many of these actions may require revalidation of the product.

The OEM should also monitor the BoM for lead-finish changes as components are converted to RoHS compliant. Many component suppliers may convert, as an example, to a matte tin or SnBi finish for components that can be used in either soldering process. Because these components are backwards comparable, the manufacturer might only provide these components in that lead finish or package style. The medical OEM should ensure the lead finish alloy is consistent with International Electronics Manufacturing Initiative (iNEMI) recommendations for reduced Sn-whisker growth. The iNEMI consortium has proposed a test to promote and accelerate whisker growth, but the test’s validity remains unproven. JEDEC/IPC Joint Publication JP002 is another document to reference, along with JESD22-A121 and JESD201.⁶

We have found some suppliers do not provide PCNs when bringing lead finishes in compliance with RoHS. It may be prudent to use XRF to monitor incoming components to ensure the leadframes are SnPb.

Tin Whiskers

Tiny strands of tin can grow and short with adjacent materials. The root causes are unknown, but lead has been used as a mitigation method for whisker growth for decades. For medical OEMs, the primary risk is the growth of whiskers from a component leadframe and potentially shorting to the adjacent leadframe. Even if the component is soldered with SnPb solder, if the component leadframe is RoHS-compliant (i.e., contains no lead), then tin whiskers could grow between these adjacent leads. This would occur above the SnPb solder joint.

Medical OEMs’ products should be analyzed for Sn-whisker risk and mitigation activities conducted. Analysis typically includes:

• Lead finish identification.
• Review of any available Sn-whisker test results.
• Whisker testing using Jedec standards (JESD-201, Class 2).
• Lead spacing evaluation.

Component lead spacing is reviewed and risk assessed based on typical Sn-whisker length. Lead spacing guide:

• >1 mm whiskers are not an issue.
• 500 µm to 1 mm some concern; testing required.
• <500 µm – must use NiPdAu/Ni underlay/anneal/fuse or reflow/A42 substrate.

Once supplier feedback is received, a decision matrix is used to determine the level and rating, assigned based on Table 3. The requirements for a test report to be considered substantially complete include:

• Test conditions.
• Test duration.
• Test vehicle.
• Test results.
• Pass/fail indication.

There are three categories within a typical test report:

1. The “Mitigation Strategy Review Status” provides the summary of the lead finish analysis and areas of concern.
   
   
2. The “Qualification Test Review Status” identifies whether whisker testing was adequate.
   
   
3. The “Overall Judgment Status” helps clarify the combined whisker risk for the product. Table 4 shows results of an analysis of an end-product with 1426 line items.

It is recommended a component engineering team familiar with the process and industry standards assist in Sn-whisker risk assessment. If component selection with the appropriate lead finish does not adequately reduce whisker risk, the OEM may want to consider conformal coating. Conformal coating an assembly will help mitigate tin whiskers; however, it will not eliminate tin whisker growth. Tin whisker growth may either occur under the conformal coating or may grow through the coating. Tin whiskers that grow through the conformal coat typically do not grow back into the coating.

Product Conversion

Several basic steps should be considered when converting a product to RoHS compliance. The engineering team should work with the supply chain and manufacturing organization throughout the conversion process:

1. Select a product representative of your other products in terms of the supply chain, component/PCB technology, and application.

2. Conduct a supply chain analysis to verify all components are RoHS compliant. This may highlight issues in the supply chain such as:

• Vendor readiness.
• Unacceptable temperature ratings (260°C is required).
• Unexpected presence of cadmium, mercury and hexavalent chromium.
• Moisture sensitivity levels (MSL) that drop 1 to 2 levels.
• Nonpreferred component surface finishes (tin whisker risk or solderability issues).
• EOL/component lifecycle issues.

3. Select a PCB laminate and surface finish.

• Laminates: MSL are critical.
• Surface finish: OSP, ENIG, ImAg and Pb-free HASL.

4. Collect the following in-process data and compare with the SnPb version of the assembly, if available:

• Inspection yields including visual inspection, AOI and AXI.
• ICT, flying probe and functional test.
• Forced rework of a through-hole component and BGA is recommended to validate the rework process.

5. Engineering should review the product’s original testing documents, and run the compliant product’s tests accordingly.

6. Select from the following tests as appropriate. It is strongly recommended the Pb-free assembly be subjected to the same tests used for the SnPb assembly, which may include additional test(s) to those recommended in Table 5.


Results from these tests will help guide the OEM to do further studies, submit to the FDA or redesign the product accordingly. In the conversion process, the first step is to scrub the BoM and identify compliant components. Some key data to capture:

• OEM part number.
• Description.
• Manufacturer.
• RoHS-compliant part number.
• Date code, if used to identify compliance.
• Some vendors did not change their part numbers, but identify compliance by date codes greater than their compliance date.
• Supplier compliance data sheet/material content.
• Homogeneous level, if available.
• Y/N at a minimum.
• Supplier material declaration document.
• Lead finish or plating.
• Tin-whisker mitigation status and test results.
• Maximum case temperature.
• MSL.

There are other factors to consider as well. When selecting components, designers should consider maximum case temperature; some components may be RoHS-compliant, but their case temperature may not survive manufacturing process temperatures. Some component lead finishes have a higher likelihood of developing tin whiskers. Material declaration should be on supplier letterhead or documentation with appropriate signature. Finally, with higher manufacturing process temperatures, many components’ MSL will change to reflect better controls for storing and handling of these materials. MSL level is critical for PCBs, and the fabricator and assembler must keep tight controls on new RoHS-compliant laminates.

When converting the BoM, the OEM may find some components unavailable or only available with lead finishes iNEMI does not recommend due to the potential of tin whiskers. This may require a level of product redesign that may result in submitting the device to the appropriate government bodies for approval. This would involve product verification and validation activities. If FDA resubmittal is required, it may be prudent to implement a full RoHS conversion of the product. In addition, when the next product generation is developed or a new product designed, a RoHS-compliant development should be considered. With the new materials used for compliance, such as assembly materials, solders, etc., the OEM may want to conduct additional reliability testing, cross-sectioning and analysis. The general consensus among participants of the IPC Pb-free Solder Reliability Conference was that long-term reliability of these new materials is not definitive. More life testing and analysis is needed.

Company/Process Conversion

Even if a medical OEM is converting its products to RoHS compliance, it might not have to have all the internal processes in place to prove compliance to any legal entity. While medical OEMs remain exempt from RoHS compliance in the EU, they should consider changing internal methods and processes to a degree that would support compliance should they convert later on.

Converting to RoHS compliance has a significant impact on documentation and documentation systems. Areas to be considered for product documentation:

• Part numbering scheme to handle and identify component compliance.
• Component specification prints/drawings should include compliance data.
• A field in the BoM to identify compliance.
• Custom part drawings and compliance language to identify compliance requirements to the custom suppliers.
• Fabrication prints and notes reflecting RoHS compliance requirements.
• Sheet metal and enclosure drawings.
• Plastic materials and enclosure drawings.
• Cable and connector drawings.

The OEM needs to make it clear to the supplier that compliance is required and the appropriate supporting documentation is available.

Many aspects of a documentation system are also affected:

• Ability to roll up component and BoM data to confirm product compliance. The OEM should determine if this could be done within the current Product Data Management (PDM) software.
• Supplier purchase order (PO) terms and agreements should reflect compliance requirements.
• Methods to request, capture and validate supplier compliance data.
• Methods to store supplier material declarations at a component level.
• Process to handle supplier certificate of compliance with each shipment.
• Process at incoming inspection to identify compliance requirements and methods to measure.
• Methods to monitor production processes in assembly manufacturing.
• Process for handling field service units to identify which products are RoHS-compliant and have appropriate repair materials available.
• Methods for approval, purchase and inspection of broker-sourced parts.

Counterfeit components have long been a problem in electronics, but lately, part counterfeiters are becoming more technically savvy. In the past, most counterfeit parts have been passives; however, now counterfeit semiconductors can be found. The level of sophistication in the packaging and labeling of counterfeit parts is alarming (Figures 1 to 4). OEMs must have special procedures for handling broker parts.


Figures 5 to 8 demonstrate labeling issues and the subtle differences between the confirmed vendor’s label and the counterfeit label. Three items were identified: 1) The RoHS label should be left-justified (Figure 5), while the counterfeit was centered; 2) there should be a period after “D.C.” (date code) (Figure 6); and 3) the “H” in the reel batch lot line was not detected by the barcode scanner (Figures 7 and 8).


Due Diligence

Establishing due diligence to monitoring and controlling operations is critical in the event a noncompliant product reaches the market and is identified by a governmental agency. The UK works with a number of EU member states on defining the approach for due diligence. For example, the Department of Trade and Industry’s “RoHS Regulations, Government Guidant Note,” of June 2006, Annex D, further defines methods. The OEM must demonstrate compliance by providing satisfactory evidence in the form of relevant technical documentation. The approach is self-declaration with the enforcement authority conducting market surveillance by testing products. OEMs should consider material declarations and material analysis as good methods for technical documentation. In Annex D, guidance is provided for material analysis based on the OEM’s confidence in the supplier’s material declaration, supplier qualification and the potential risk of the material containing a restricted substance based on historical data. This supplier documentation should be maintained for up to four years.⁷

A due diligence process should be defined within your organization to help ensure compliance. One method is to base this process on a “trust, but verify” approach. It begins with capturing the product documentation for compliance. This information is stored and internal flags are set so the appropriate procedures are followed to handle this compliant material. This involves many areas, ranging from purchasing, incoming, warehouse, kit-pull, production and shipping. XRF is a key capability deployed at a number of process steps. At a minimum, this is used at incoming inspection, process monitoring (i.e., soldering materials) and shipping. Some considerations when using XRF include a method to handle failures because of exempt product (i.e., lead in glass) and failures due to supplier issues. Methods should quickly identify exempt failures, which can be ignored, versus legitimate failures as a result of supplier issues. The procedures for supplier failures should quickly determine root cause and also track and trend supplier performance.

Another consideration is the effectiveness of an XRF in isolating hexavalent chrome (Cr6). XRF will detect the base element (chromium), but not the compound (Cr6). Secondary laboratory tests would be needed (wet chemical test) to detect the banned Cr6 substance. Another option upon getting a high chromium reading is to contact the vendor; if they are reputable and confirm in writing the chromium is not the banned form, this could be considered an appropriate level of due diligence.

Case Study

Benchmark typically provides both EOL and RoHS BoM analysis for customers. Six different medical products were analyzed for this paper. The cycle time for this analysis can run from three weeks to four months, depending on BoM size and supplier responsiveness. Three passes are performed on the BoM.

This approach begins by first evaluating the BoM for completeness and accuracy. Typically, a number of components have inaccurate manufacturer and manufacturer part numbers. Second, Web-based databases are used for the initial data collection. The hit rate for data from these databases is typically 50 to 70% for EOL status. RoHS compliance identified in the database is typically 10 to 20% in a “Yes/No” format and <5% at a homogeneous material level. The final pass involves component engineers who work directly with the supplier. When contacting the supplier directly, homogeneous level information is typically provided in 10% of the cases. With a strong supplier relationship, this can be increased to 50 to 70%. Also with direct supplier contact, we typically achieve 90 to 95% EOL status.

There are three statuses provided:

1. The BoM is scrubbed in its current state and components are classified as planned (not yet released), preliminary (data sheet is preliminary), active (available), NRND (not recommended for new design) and EOL.
   
   
2. The second report looks at the EOL detail and identifies what is currently obsolete, which year a component is predicted to go obsolete, which ones are planned for obsolescence (no time frame identified) and which are not planned for obsolescence.
   
   
3. The RoHS report identifies parts as compliant (RoHS available with an existing part number), available (RoHS with a new part number), probable compliant (vendor implies compliance), planned (scheduled), not available and EOL. It should be noted material that is EOL on the existing BoM may be available in the RoHS BoM. This is an indicator of vendors that are obsoleting SnPb components in favor of RoHS-compliant packages. This may be a risk for maintaining a SnPb product. EOL material identified in the RoHS status is a risk for long-term product sustainability.

Results. Across these six different medical products, some interesting statistics were identified. On average for RoHS-converted BoMs:

• 92% (range 88 to 99%) of the components were available in a RoHS-compliant package.
• 56% (range 31 to 99%) of the components’ part numbers were not changed when converted to RoHS.
• 2% (range 0 to 4%) of the components on the RoHS BoMs were EOL.
• 1% (range 0 to 2.6%) of the components was not available in a RoHS package.

On an average for the SnPb BoMs:

• 8% (range 0 to 16%) of the SnPb components were NRND.
• 4% (range 0 to 14%) of the SnPb components were becoming obsolete (component EOL, RoHS-compliant only).
• 12% (range 0 to 29%) of the SnPb components fell into either NRND or obsolete categories.

Key observations for these six BoMs:

• No BoM was completely converted to RoHS compliance. At least one part would require an alternate or redesign.
• For the SnPb BoMs, 12% of the components were obsolete or NRND. For the RoHS BoMs, 2% of the components were obsolete. This would suggest a number of components are transitioning to RoHS compliance and are no longer available in a SnPb package.

Conclusions

Current environmental requirements and regulations for compliance indicate the medical market has anywhere from four to 12 years before its products must be compliant. Based on the length of a new medical product development cycle, clinicals, the cost of validation and FDA submittal, medical OEMs should be positioning themselves to be compliant. Long product life within the medical market would suggest OEMs’ new products be released already compliant, versus trying to convert a product later and risk revalidation and FDA submittal. Tin whisker risk mitigation strategies should be adopted to reduce potential problems.

At a minimum, medical OEMs should be monitoring current product components and BoMs for obsolescence, to avoid production flow impacts. Component packaging should be monitored to detect changes in lead finish and associated Sn-whisker risk, along with monitoring BGA ball alloys to identify solderability and process risks. The medical OEM should monitor the BoMs/components of the current production products to ensure supply and new product designs are compliant. Internal procedures and methods should be updated so internal processes can be monitored to ensure new products will ship compliant.

References

1. Dr. Paul Goodman, “Review of Categories 8 and 9 and the RoHS Directive,” IPC Webinar, February 2007.
2. Dr. Paul Goodman and Dr. Chris Robertson, “Review of Directive 2002/95/EC (RoHS) Categories 8 and 9 – Final Report,” September 2006.
3. Jonny Evans, “Greenpeace: Apple iPhone is Hazardous: iPhone Contains Toxins Others Don’t Use,” ComputerWorldUK, October 15, 2007.
4. ESB, “The End of Leaded Commercial Parts: Part 2,” May 3, 2006.
5. Ibid.
6. Jedec/IPC JP-002, “Current Tin Whiskers Theory and Mitigation Practices Guideline,” March 2006.
7. DTI, RoHS Regulations, Government Guidance Note, June 2006.

Ed.: This article was first published at the SMTA Medical Electronics Symposium in January 2008 and is used with permission.

Kim Sharpe is corporate director of engineering at Benchmark Electronics (bench.com); kim.sharpe@bench.com.

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