By
Dr. Greg Jones
KIC Thermal Profiling San Diego, California With the arrival of the 21st century, the shift to lead-free electronic assembly appears to be a certainty. Barring unforeseen developments, the production and import of leaded solders and electronic components will be banned in Europe by 2004. In Japan, the electronics industry is voluntarily removing lead from its products. Each company has set its own goals, with some, like Sony, planning to be completely lead-free by 2001. Most plan to become lead-free between 2002 and 2005. To date, there has been no discussion of banning imports containing lead from the Japanese market. Given the environmental issues driving the shift, however, this issue will surface eventually. In the United States, the situation is more ambiguous. While it appears unlikely that there will be any legislative efforts to ban lead in the domestic electronics industry, other issues make it likely that the U.S.-based industry will follow the European and Japanese examples. The Situation In the past year, there was some uncertainty in the U.S. over whether the European directive would be implemented. It is now certain that the WEEE (Waste Electrical and Electronic Equipment) directive will be implemented. This implementation has been recognized by the major U.S. trade associations. Follow-ing IPC Works99, where an international summit on lead-free electronics assembly was held, there can be little doubt that lead-free is not just coming but is here1.Legal Status Japan: Japan has a severe problem with solid waste. All available landfill is expected to be filled by 2007. The Japanese are very concerned with removing toxins from their environment and want to remove lead from waste to prevent its leaching into groundwater. In 1998, the Japanese Electronics Industries Association decided to voluntarily eliminate lead from electronic assemblies. The goal of the association is for half of Japanese electronics production to be lead-free by 2002, and to be completely lead-free by 2004. Europe: The final draft of the WEEE Directive was to be completed in January. It is certain that electronic assemblies containing lead will be banned from the European Union as of January 2004. The motivation behind this ban is that electronics waste is growing at a rate three times greater than other solid wastes. This huge increase in the amount of electronics waste has raised concerns about lead leaching into water supplies. United States: Ironically, the initial impulse for lead-free electronics originated in the United States. Following the ban on leaded plumbing solders in the early 1980s, electronics assembly was seen as the next logical industry from which to remove lead. The Reid Act of 1992, an omnibus environ-mental bill, would have done that, but it was defeated. Currently, there is no legislation proposing a ban on leaded solder; still, there are some legal threats on the horizon. For example, the EPA may reduce the regulatory limit on lead as a hazardous material from 10,000 pounds per year to 10 pounds per year, making almost every user of leaded solders subject to EPA regulation, reporting and inspection. It is unlikely that leaded solders will be banned in the United States in the near future, but there are many compelling reasons that will motivate most U.S. electronics assemblers to go lead-free. International: One further issue of concern to all electronics manufacturers is that the European ban and the potential for a Japanese ban may touch off trade disputes. Anyone who has followed the disputes over relatively "insignificant" products, such as bananas, knows that we must avoid a major trade war involving one of the world's largest and most critical industries. Marketing Advantages Many observers of the lead-free solder issue feel that the legal points are moot, and that marketing considerations alone will force a change to lead-free electronics in the near future. Japanese electronics manufacturers have taken the lead in "green" marketing. Panasonic's lead-free mini-disc player, packaged with a green leaf environmentally safe symbol and released in October 1998, has gained significant increases in market share, moving from 4.7% of the mini-disc market to 15%2 In the U.S., Ford Motor Company has launched what is perhaps the largest green marketing campaign to date. Ford has gone on record declaring that its electronic assemblies will be lead-free by 2002. Its vehicles, the company promises, will be lead-free by 2004. Green marketing is viewed as becoming a powerful and effective marketing tool, and many electronics manufacturers are going to take advantage of it by going lead-free. The Next Hurdle Controversy over lead-free solders has shifted from whether they are adequate replacements for traditional lead/tin solders to which possible replacement alloy will be selected as a new standard. This standard will be critical. Currently, electronic assemblies can be repaired worldwide with standard leaded solder. There are numerous solderability and wetting issues between lead solders and lead-free solders. Among these issues, lead-free solders wet poorly to components with leads that contain lead. Further muddying the waters are compatibility issues among various lead-free alloys. It is imperative that the global electronics industry settle on a single standard alloy to ensure that assemblies can be repaired expeditiously and reliably. Another downstream issue is recyclability of assemblies. A single standard alloy will make it much more feasible to recover and recycle base metals. To date, most paste suppliers and many electronics manufacturers have developed proprietary alloys. Obviously, it is in the best interests of the holders of these patents to have their alloy selected as the standard, and an enormous amount of research is being done to establish a winner. There are also many unpatented alternatives. The alloys that appear most likely to become the industry standard are Sn/Ag/Cu and Sn/Ag/Bi. The choice between the two involves a tradeoff. Sn/Ag/Cu provides solder joints that may be as reliable as the current Pb/Sn alloys and features liquidus temperatures around 217oC. The majority of Americans and Europeans favor an Sn/Ag/Cu alloy as the standard because of its potential for greater reliability and lower cost, while acknowledging that the higher process temperatures that these alloys require present a challenge for assemblers. The bismuth alloys provide solder joints that are in some ways inferior to those provided by current leaded solders (due mostly to a phenomenon known as "fillet lifting") and offer liquidus temperatures ranging from 206oC to 213oC. Bismuth alloys, which appear to provide adequate reliability for most consumer uses, are preferred by some because they are the closest thing to a "drop in" replacement for leaded solders. These alloys are also favored by the Japanese and are currently used in the lead-free electronic assemblies that are on the market. The bismuth alloys are more expensive than Sn/Ag/Cu alloys, however, and there are concerns that the world's current bismuth resources may be inadequate to meet prospective demand. Further concerns are, that as a lead byproduct, bismuth may be subject to a later ban, and that bismuth alloy solders are difficult to produce in wire form. Both bismuth alloys and Sn/Ag/Cu alloys are being extensively tested and will be used in volume production beginning this year. An additional factor affecting the choice of a standard alloy is that the Sn/Ag/Cu alloys are favored by the automotive industry, because their higher melting points will give better reliability in under-hood applications. Further testing needs to be done on the reliability characteristics of both alloys before an informed desision on a standard alloy can be made. The Challenge The move to lead-free electronics assembly presents component makers with a three-part challenge: First, they must remove lead from their products; next, they must develop leads that are compatible with lead-free solders; and, eventually, they will need to develop components with higher temperature tolerances. The first two tasks must be completed to successfully assemble products that meet European standards. This leaves the question of whether component manufacturers will be able to raise their temperature tolerances in the short term. Over the longer term, the question is whether raising the process temperature limits of components will be economically justifiable, or even necessary. Technical Problems The chief technical problems associated with the adoption of lead-free electronic assembly are: Component lead solderability issues: There are serious issues with solder joints between leaded leads and lead-free solders. Alternative lead finishes, that are mostly palladium-based, have been developed. The fallout on this issue will be chiefly economic, involving the costs associated with developing and implementing new processes, as well as the greater expense of more costly lead-finish materials. Alloy selection: It is critical that a common replacement for Sn63Pb37 leaded solder be agreed on by the worldwide electronics industry. The IPC is aggressively pursuing agreement on a common alloy. This will be discussed at the IPC's winter meeting and also at APEX. The goal is a short list of potential standard alloys by this April. The effects of lead-free assembly on sophisticated modern ICs, such as BGAs: The main issues are the effects of higher reflow temperatures on IC package substrates and the reliability of lead-free solder joints, specifically shear strength and intermetallic growth. While research is being conducted by most of the semiconductor industry's major players, very few of their findings have been made public.
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