Contrary to conventional wisdom, drivers for environmentally safe products exist in addition to government legislation. Electronic companies are concerned about environmentally safe designs, manufacturing processes and product recycling. What's more, from the commercial side, environmentally friendly products appeal to consumers who, with each generation, are becoming more environmentally conscious. Progress is slow, but steady, toward environmental stewardship. However, unquestionably new environmental legislation has jumped in the driver's seat and is racing to more immediate action.
Recently, project-oriented environmental legislation in Europe has been drafted to resolve environmental issues which, in turn, affects all electronic products sold and manufactured in Europe. This legislation, with overwhelming new requirements and optimistic introduction timing, has spawned a flurry of development and application panics in the electronics industry.
The European Union (EU) drafted two directives in 1997 that, if enacted, will have a significant effect on electronic product designs. The first is the Waste from Electric and Electronic Equipment (WEEE) directive. Its intent is to prevent waste, promote recovery, encourage recycling and minimize environmental impact. Even though this directive includes many issues, eliminating lead metal has received the most attention. As written, lead metal will be banned from all electronic products manufactured in and imported into Europe starting in January 2004.
The second directive is the End-of-Life Vehicle (ELV). This directive focuses on the automotive industry with two significant goals: cost-free take-back for new vehicles entering the European market after January 2001 and cost-free take-back of all vehicles in the EU fleet after January 2006. Vehicle take-back will inspire local recycling and require conformance to stringent disposal requirements. Today, lead metal in electronic solders is exempt from the ELV directive; other uses of lead are not exempt. However, OEMs will undoubtedly apply pressure to eliminate lead in electronics if the WEEE directive is enacted at a later date.
Both EU directives are changing and evolving, with implementation dates being extended and content being rewritten. The ELV directive is being considered first; final resolution is expected this calendar year. The WEEE directive is still in a draft revision state with an undetermined enactment date.
Technically, what are the issues? Eutectic 63Sn37Pb or near eutectic 60Sn40Pb solder are the most commonly used solders in the manufacture of electronic assemblies. Components, substrates and manufacturing equipment have all been designed specifically for its use. Quality manufacturing processes have been developed and analyzed, and in-depth knowledge of PnSn solder reliability during operational life has been accumulated.
In other words, tin/lead solders have become a major material constant in electronic assembly and they are well understood. Now the industry is faced with selecting a new lead-free solder material that might require a total infrastructure change. Regardless of which lead-free solder becomes the new standard, it will not have the industry familiarity of tin/lead.
Many companies and industry consortia have been working on lead-free processing for the past 10 years. Major activities have been conducted by the National Center for Manufacturing Sciences, International Tin Research Institute, Swedish Institute of Production Engineering Research, Japan Institute of Electronic Packaging, Improved Design Life and Environmentally Aware Manufacturing of Electronic Assemblies by Lead-free Soldering, and, more recently, by the National Electronics Manufacturing Initiative (NEMI-USA). As a result of these efforts, new solder alloys have been identified and tested on products with very encouraging results. But some serious issues need to be resolved in large volume production of lead-free electronic assemblies.
The most significant issue is components. Most of the lead-free solders considered as broad-based replacements for tin/lead have a higher melting point. For example, the 95.5 Sn3.8Ag0.7Cu selected by NEMI has a 34°C higher melting point than tin/lead.
This increased temperature could have an adverse effect on components when the solder is applied during component fabrication, and at assembly in the solder wave or solder reflow process. Plastic IC packages, capacitors, inductors and chokes could be problematic due to entrapped moisture (popcorning) or other deleterious effects.
Organic laminated printed wiring boards, which are commonly used, are not designed for higher processing temperatures. While high-temperature laminates have been developed, they are only available in limited production and at higher costs. Board-surface finishes will also have to be lead-free, creating the need for common hot air solder leveled finishes to be replaced with more costly electroplated finishes, such as gold, tin or silver. And, to top it off, there are issues of assembly material and component interconnect compatibility that will also have to be addressed.
It should be noted that lead-free assemblies cannot be produced with components that contain lead. Products produced with lead-free interconnect solders and lead containing components should be designated “lead-lite” (reduced lead content). This term is yet to be defined by industry or government. How much lead is really too much? What are the specifications?
There's no question that pending legislation is saying, “Get the lead out!” For now, solders and processes that produce reliable products have been developed, but they are not simple drop-in substitutes for tin/lead. The major technical hurdles that remain lie in components and printed wiring boards. And don't be fooled by “lead-lite” – what legislation is mandating is lead-free.
DANIEL K. WARD is manager of advanced electronic packaging for Delphi Delco Electronics Systems, One Corporate Center, P.O. Box 9005, Mail Station: D-16, Kokomo, IN 46904-9005; 765-451-3093; Fax: 765-451-3115; E-mail: email@example.com.