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Moving Toward Lead-Free Products

  Originally Published MDDI May 2005 Medical Electronics Moving Toward Lead-Free Products

Originally Published MDDI May 2005

Medical Electronics

Moving Toward Lead-Free Products

Although medical devices will not need to be lead free by the July 1, 2006 deadline, manufacturers should start to address their use of lead-bearing solder.

Dean Miller

This acoustic image shows internal features of a thin, small-outline package in a tray before placement (left) and after placement and reflow (right). Conventional lead-based solder was used for both paste and plating of leads. There are no delaminations, cracks, or other internal defects (click to enlarge).
A thin, small-outline package before placement (left) and after placement and reflow (right). Lead-free solder was used both for plating of leads and for paste. The
higher reflow temperatures have caused internal delaminations (red areas) (click to enlarge).

The European Commission (EC) issued two directives in early 2003 with the goal of dramatically cutting down on toxic materials in municipal waste. A large part of the legislation focuses on eliminating the use of lead, in particular, the use of lead-bearing solder, in electrical and electronic equipment. This article focuses on how these directives may affect the use of lead-bearing solder on printed circuit boards (PCBs) in medical devices.

If eliminating lead on PCBs was easy to do and raised no reliability concerns, there would be no reason for concern. As responsible members of the community, we would all convert to lead-free assembly right away. But there are such concerns, and the conversion itself is not completely straightforward.

WEEE

The EC issued the Waste Electrical and Electronic Equipment (WEEE) Directive in January 2003.1,2 It is intended to prevent potentially hazardous waste, such as old television sets and out-of-date computers, from contaminating the environment. To that end, it calls for this material to be reused, recycled, and recovered. Incineration and disposal of equipment in landfills are no longer acceptable alternatives.

The directive calls for labeling to warn consumers and end-users that these products may not be dumped in the trash bin. It also requires that manufacturers and distributors establish procedures for proper disposal at their own expense.
According to annex IA, the WEEE Directive is applicable to the following products:

• Household appliances.
• IT/telecommunications equipment.
• Consumer equipment.
• Lighting equipment.
• Electrical and electronic tools (excepting large-scale stationary industrial tools).
• Toys and leisure and sports equipment.
• Medical devices (excepting all implanted and infected products).
• Monitoring and control instruments.
• Automatic dispensers.

It is fairly clear why implanted and contaminated medical devices are exempt; they often must be handled with greater care. But manufacturers of medical electrical equipment (e.g., electrocardiograph machines, radio-frequency generators, patient monitors, etc.) must have the labeling and facilities in place for proper waste recovery by August 13, 2005. Although the WEEE Directive is relevant for medical devices, it does not answer the question about whether PCBs, including those in medical devices, must be lead free.

RoHS
The Restriction of Hazardous Substances (RoHS) Directive was issued at the same time as the WEEE Directive.3 WEEE describes what should be done with waste equipment; RoHS describes what substances must be excluded from the devices in the first place.

Article 4 of the RoHS Directive requires that as of July 1, 2006, new electrical and electronic equipment put on the market must not contain the following materials:

• Lead.
• Mercury.
• Cadmium.
• Hexavalent chromium.
• Polybrominated biphenyls (PBB).
• Polybrominated diphenyl ethers (PBDE).

Other national regulations have restricted the use of PBB and PBDE for several years.4 As a result, these requirements are not new to most manufacturers. Hexavalent chromium and cadmium are seldom used in electronic systems. Mercury, which might be used in relays, could cause problems on PCBs. But the requirement to remove lead from solder, specifically solder on PCBs, causes significant concern for manufacturers.

The RoHS annex describes certain exemptions for lead-bearing solders:

• Lead in high-melting-temperature-type solders (e.g., tin-lead solder alloys containing more than 85% lead).
• Lead in solders for servers, storage, and storage-array systems (exemption granted until 2010).
• Lead in solders for network infrastructure equipment for switching, signaling, transmission, and network management for telecommunications.
• Lead in electronic ceramic parts (e.g., piezoelectronic devices).

The application-specific exemptions have been the subject of recent review. The EC issued a request for industry comments on a possible amendment of the RoHS annex.5 It also commissioned ERA Technology, a UK consulting firm, to address the proposed amendments point by point. In the ERA report, the conclusion regarding the use of lead in solders for servers was the following:

There is a risk to consumer safety should these systems fail unexpectedly. The reliability of lead-free solders is being researched using accelerated testing. It is not yet known, however, how to extrapolate accelerated test data to predict field performance, and this will not be possible until lead-free solders have been in widespread use for at least five years.6

The latest from the EC is the “Unofficial Note of the Technical Adaptation Committee on the WEEE and RoHS Directives,” dated December 10, 2004.7 In that memorandum, the committee stated that parts of the RoHS annex would be combined to include lead in solders for servers; storage and storage array systems; and network infrastructure equipment for switching, signaling, and transmission; as well as network management for telecommunications.

The EC has removed the condition that the exemption on using lead-bearing solder in servers be stopped by 2010. It recognizes that a reliability issue must be addressed and is relaxing, not tightening, the rules.

Although not directly applicable to medical devices, the relaxation indicates the EC's thoughts about lead-bearing solder. It recognizes that determining the effects on long-term reliability will take time. It also shows that the EC understands that the critical nature of some systems requires that no chances be taken. After all, it is one thing to have a television set fail and quite another to have a data server or a life-support system malfunction.

RoHS and Medical Devices

Currently, medical devices are exempted from the RoHS Directive requirements. Article 2 (Scope) of the RoHS directive states the following:

1. Without prejudice to Article 6, this Directive shall apply to electrical and electronic equipment falling under the categories 1, 2, 3, 4, 5, 6, 7, and 10 set out in Annex IA to Directive No 2002/96/EC (WEEE) and to electric light bulbs, and luminaires in households.
2. This Directive shall apply without prejudice to Community legislation on safety and health requirements and specific Community waste management legislation.
3. This Directive does not apply to spare parts for the repair, or to the reuse, of electrical and electronic equipment put on the market before 1 July 2006.

Note that categories 8 (medical devices) and 9 (monitoring and control instruments) are not covered by the directive. In fact, implanted and contaminated medical devices are beyond the scope of both WEEE and RoHS.

Article 6 (Review) of RoHS states

Before 13 February 2005, the Commission shall review the measures provided for in this Directive to take into account, as necessary, new scientific evidence.

In particular the Commission shall, by that date, present proposals for including in the scope of this Directive equipment, which falls under categories 8 and 9 set out in Annex IA to Directive 2002/96/EC (WEEE).

The Commission shall also study the need to adapt the list of substances of Article 4(1), on the basis of scientific facts and taking the precautionary principle into account, and present proposals to the European Parliament and Council for such adaptations, if appropriate.

Particular attention shall be paid during the review to the impact on the environment and on human health of other hazardous substances and materials used in electrical and electronic equipment. The Commission shall examine the feasibility of replacing such substances and materials and shall present proposals to the European Parliament and to the Council in order to extend the scope of Article 4, as appropriate.

It is unclear whether any action is pending at the EC that would cause the exemption of medical devices to be removed or even be reexamined. It is always difficult to prove that no action is pending within a regulatory body, but to date nothing has surfaced. All signs seem to show that the medical device exemption will remain in the directive for the foreseeable future. It is very clear that the 2006 deadline is not applicable for medical devices now and there has been no move yet to make them subject to the RoHS directive.

The bonus of keeping the status quo is that the medical device industry has some time to prepare. Device manufacturers can use the time to monitor the progress made by other industries and learn from their mistakes and successes. Medical devices can, and arguably should, be made lead-free.

Problems with Lead-Free Assembly

So why not just convert to lead-free assemblies right now? Other industries are making the conversion. There are two key reasons to stay with tin-lead (SnPb) solder for now.

First, lead-free solder processes expose the boards to considerably higher temperatures than SnPb solders. Some components cannot handle the higher temperatures. For others, exposure to higher temperatures calls parts' long-term reliability into question.

Second, it takes a long time to bring new or modified medical devices to the market. Product life cycles are not measured in months like they are in the home entertainment industry, but rather in years. It takes more time to validate the processes because the stakes are higher than in some other industries.

EUCOMED, the European association representing the interests of the medical technology industry, submitted a well-reasoned response to the EC call for comments on proposed amendments to the RoHS Directive.8 In that memorandum, EUCOMED said that it was important that the exemption remain in effect for a considerable length of time. EUCOMED concluded

Many medical devices are used in critical care areas with great demand on reliability. Technologies used to date are well understood and reliability can be predicted with reasonable certainty. To change from well understood technology to technology of an uncertain pedigree should not be undertaken without a risk analysis based on adequate data. Medical devices should therefore be allowed to lag behind other sectors to the point where sufficient data is available from which to make informed assessments, before switching to new materials or manufacturing processes.

EUCOMED's response also referred to the Medical Devices Directive (93/42/EC), which requires adequate data to demonstrate that devices are safe. As a minimum, EUCOMED recommended at least five additional years be granted for medical devices.

Industry in Transition

What must medical device manufacturers do to prepare for transition? Some component manufacturers are already changing their lines to remove parts with SnPb-plated leads in favor of lead-free parts. This change may make some currently used parts hard to find. Does this mean that medical device manufacturers must make lifetime purchases or face a production shutdown? Not necessarily.

The majority of these new parts are fully compatible with the conventional SnPb soldering processes. Component manufacturers usually provide good explanations of the issues involved. Some handling changes may be required, but, with few exceptions, there is little concern when replacing a conventional part with one having lead-free plating on the leads.
In some cases, the lead-free parts will have the same part numbers as the SnPb parts. In those cases, little or nothing may need to be done to continue production. If the lead-free parts have new part numbers, revising the approved supplier list (ASL) to incorporate the new parts is usually adequate. However, this is only true if the new part is backward compatible with the existing assembly processes. The manufacturer, in cooperation with the component manufacturer and PCB assembly team, must make and document that decision.

Of course, some medical devices are of such a nature that even a minute process or component change must be validated; for most devices, that is not the case. Again, the manufacturer must make that decision for each affected product.

Some components are already RoHS compliant, using lead-free terminations, and have been for several years. Consider the following statement from Kemet Electronics (Greenville, SC):

Lead was eliminated from our ceramic surface-mount plating process over a decade ago. Billions of these parts have been successfully used in both historic tin-lead and higher temp lead-free soldering processes.9

In general, using lead-free parts with conventional SnPb solder processes is not a problem. In some cases, companies have been doing it all along.

Nevertheless, there is a notable exception. Ball-grid array (BGA) parts are made with a small ball of solder for each contact; they do not have normal plated leads. What happens when a BGA part is only available with lead-free contacts? If processed with a SnPb solder paste and reflow profile, will the joint be reliable? The short answer is no.10 This is one area in which a lifetime buy may be necessary. The good news, though, is that most manufacturers probably have only a small number of BGA parts. In addition, BGA part manufacturers know that there are companies that will not change to lead-free parts any time soon. But it is still important to check with your suppliers even if you expect those manufacturers to offer leaded and lead-free BGA packages for years.

The PCBs that most of us have become accustomed to using are made of FR4 material, and the plating is usually hot-air-leveled SnPb. Although the SnPb plating will probably be available for some time, FR4 material may be phased out. The rest of the industry will be switching to lead-free processes, which will require the use of FR406, FR408, and other materials to handle the higher process temperatures.

Fortunately, these new board materials can still be used with conventional SnPb solder. Even if hot-air-leveled SnPb plating becomes unavailable, other lead-free plating materials could be used with SnPb solder. Device manufacturers will need to update board fabrication drawings and specifications but will not need to change the layout.

A problem would arise if suppliers stopped offering SnPb solder, but that is unlikely to happen. After all, it is likely that military and avionics equipment will continue to use SnPb solder beyond the time that the medical device industry makes the switch.

Steps to take to prepare for the switch include the following:

• Review products to determine whether the change to lead-free parts could require validation prior to implementation. You should do this even if the soldering process remains the same. If so, perform that validation. Remember to document your decision.
• Determine the strategy of each component supplier with respect to the transition to lead-free parts. Will they continue to offer the old parts? Will they be changing the part numbers? Are there any new parts that have not been validated by the supplier with conventional (SnPb) soldering processes?
• Pay particular attention to BGA parts and any others that might be incompatible with the SnPb process if they were converted to be lead-free. Work closely with suppliers and consider a lifetime buy if necessary. (Here is a potential for serious problems. If the part manufacturer is not going to continue to offer the SnPb BGA part, if the new part cannot be proven reliable with the SnPb process, and if a lifetime buy is impractical, you may be forced to use a carrier device or even to convert to lead-free sooner rather than later.)
• Update your ASL to include the new manufacturer's part numbers as needed.
• Update your board fabrication drawings and specifications to permit the use of new materials as needed.
• Plan ahead. Anticipate the switch to lead-free processing so that when it happens it won't be a crisis.

There is also one important assembly issue. Existing wave-solder equipment cannot be switched back and forth between SnPb solder and lead-free solder. It will be important to verify that your PCB assembler will continue to support the use of SnPb solder for as long as you require. That may take some negotiating, since some contract manufacturers are trying to establish lead-free shops.

Fully Lead-Free Products

There will come a day when you do want to make the switch and eliminate the use of lead solder altogether. That day may come through regulation, it may be caused by lack of availability of SnPb BGA parts, or it may arrive as a result of other business decisions. It is unlikely that the industry will remain leaded indefinitely.

How you proceed depends on where you are in the product life cycle. If you have a product that is still in the development stage, it may be best to plan for lead-free assembly now, relying on the SnPb soldering process if possible but doing everything else as if the product was going to be lead-free.

If practical, consider doing a PCB layout so that a relayout won't be necessary later. (Device land patterns and trace spacing may need to be adjusted slightly for lead-free assembly. In addition, vias may need to be altered for the lead-free process.) Review the layout to ensure that it is compatible with both SnPb and lead-free processes.

Most of all, stay in close touch with your suppliers. They are your partners, but they also have other partners who are required to switch to fully lead-free assemblies.

References

1. “Directive 2002/96/EC of the European Parliament and of the Council of 27 January 2003 on Waste Electrical and Electronic Equipment (WEEE)” [on-line] Official Journal of the European Union
L37 (2003): 24–38; available from Internet: http://europa.eu.int/eur-lex/lex/LexUriServ/LexUriServ.do?uri=CELEX:32002L0096:EN:html.

2. “Directive 2003/108/EC of the European Parliament and of the Council of 8 December 2003 Amending Directive 2002/96/EC on Waste Electrical and Electronic Equipment (WEEE)” [on-line] Official Journal of the European Union L345 (2003): 106–107; available from Internet: http://europa.eu.int/eur-lex/pri/en/oj/dat/2003/l_345/l_34520031231en01060107.pdf.

3. “Directive 2002/95/EC of the European Parliament and of the Council of 27 January 2003 on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment” [on-line] Official Journal of the European Union L37 (2003): 19–23; available from Internet: http://europa.eu.int/eur-lex/lex/LexUriServ/LexUriServ.do?uri=CELEX:32002L0095:EN:html.

4. C Lassen, S Løkke, and LI Andersen, “Brominated Flame Retardants: Substance Flow Analysis and Assessment of Alternatives” [on-line] Danish Environmental Protection Agency, Section 5.3, Table 5.1, (1999); available from Internet: www.mst.dk/udgiv/Publications/1999/87-7909-416-3/html/default_eng.htm.

5. “Stakeholder Consultation on Adaptation to Scientific and Technical Progress under Directive 2002/95/EC of the European Parliament and of the Council on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment for the Purpose of a Possible Amendment of the Annex” [on-line] (Brussels: European Commission, DG Environment, Unit G4, 2004); available from Internet: http://europa.eu.int/comm/environment/waste/pdf_comments/rohs_consult.pdf.

6. P Goodman, P Strudwick, and R Skipper, “ERA Report 2004-0603: Reliability and Failure Analysis: Technical Adaptation under Directive 2002/95/EC (RoHS)—Investigation of Exemptions” [on-line] (Surrey, UK: ERA Technology, 2004); available from Internet: http://europa.eu.int/comm/environment/waste/pdf/era_technology_study_12_2004.pdf.

7. “Unofficial Note of the Technical Adaptation Committee on the WEEE & RoHS Directives” [on-line] (Brussels: Technical Adaptation Committee, 2004); available from Internet: www.dti.gov.uk/sustainability/weee/TAC_10_December.pdf.

8. “EUCOMED Response to European Commission Public Consultation on RoHS Directive” [on-line] (Woluwe-St. Lambert, Belgium: EUCOMED, 2004); available from Internet: www.eucomed.be/docs/ EC_RoHS_Annex_Submission_Final.pdf.

9. “Green Product Roadmap, RoHS Compliance and Lead-Free Status” [on-line] (Greenville, SC: Kemet Electronics 2005); available from Internet: www.kemet.com/kemet/web/homepage/kechome.nsf/vabypagename/Greenproduct.

10. C Handwerker, “Transitioning to Lead-Free Assemblies” [on-line] Printed Circuit Design and Manufacturing 22, no. 3 (2005): 17–23; available from Internet: www.pcdandm.com/pcdmag/mag/0503/0503inemi.pdf.

Dean Miller is founder of Dean Miller Associates (Menlo Park, CA).

Copyright ©2005 Medical Device & Diagnostic Industry

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