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Although metals have played a key role in human history, only the most easily extracted and least reactive metals such as copper, iron, zinc, tin and lead were widely known and used in prehistoric times. Lead, of course, has been known for thousands of years; Roman citizens often used lead acetate (“Sugar of Lead”) as an artificial sweetener and lead pipes have been used for water distribution for centuries because the metal is largely unaffected by water, organic solvents and dilute acids and alkalis.  Developed within the ECOPACK® program, in 2000, ST annonced a lead-free Ball Grid Array package in whinch the conventional tin/lead solder balls are replaced by a tin/silver/copper alloy — part of the Company’s commitment to achieve total environmental neutrality. Mediaeval alchemists, who rarely had to sign off profit and loss accounts, were free to pursue “pure” research goals such as the “Elixir of Youth”, the “Universal Solvent” and, most famously, the secret of turning lead into gold. In fact, physicists have been able to turn lead atoms into gold atoms for more than half a century but no-one has yet been able to convert this triumphant validation of theoretical physics into a commercial opportunity. Useful but Dangerous Some historians have speculated that the decline of the Roman Empire was partially due to lead poisoning; and there is much scientific evidence that lead is highly damaging to human beings. Unfortunately, lead also has properties that make it hard to replace in some applications; most cars today can run happily on lead-free petrol but their batteries still rely on the classic lead-sulphuric acid reaction. In the electronics industry, lead is deeply entrenched. It is one half of the lead/tin eutectic known as solder which is an alloy that has the useful property of not only forming good electrical connections with other metals such as copper and silver and this at the relatively low temperature of 183°C. Today, and in the foreseeable future, once lead has been extracted from its environmentally innocent ore and used for human purposes, it becomes a threat; useful, irreplaceable sometimes, but dangerous both in the short term and the long term. For obvious reasons, the electronics industry would like to dispense with lead and ST and many other semiconductor manufacturers and equipment manufacturers have serious, well-funded research programs aimed at finding alternative solutions. However, the hard reality of commercial life is that alternative solutions have to be economically viable. Nonetheless, responsible companies DO care about the kind of world they are bequeathing to future generations and try to find solutions to the difficult task of balancing short-term economic pressures and longer term visions of environmental neutrality. The more difficult part may be to sell the products to customers who accept the principle but have their own customers to sell to ... and the question, sooner or later, is “How much does it cost?” The answer to this question will vary enormously in different industries and in different applications within the same industry but it is hard to oppose the argument that the higher up in the food chain you are, the more impact you have on all the dependent levels. If the electronics industry is going to eliminate lead from its products, it will only do so if the semiconductor industry comes up with an economically viable alternative.  The reliability of solder joints can be affected by the formation of tin extrusions known as whiskers. A standard test is required so that this risk can be assessed in a consistent manner for all proposed lead-free solders. Taking the Lead In a move aimed at accelerating the use of lead-free packages and stimulating the further development of lead-free technologies, ST has been working with a number of other semiconductor manufacturers and materials suppliers on this issue. One of the results is a series of proposals for the world’s first standard for evaluating “lead free” semiconductor devices. “At present, there isn’t even an internationally agreed definition of the term “lead-free” because it is very difficult to remove every trace of lead from other metals”, says Carlo Cognetti, ST’s VP for New Package Development. “Our customers want to know how to evaluate our lead-free solutions against those of our competitors and they need to be able to calculate the impact that lead-free technology will have on their bottom line. If they switch to lead-free technologies, will their manufacturing costs increase and will the reliability of their products be affected by the higher soldering temperatures?” One of the major barriers to the elimination of lead is the lack of internationally agreed standards and methodologies for evaluating the quality and reliability of lead-free technologies. In contrast, because a single lead-tin alloy has been used for many decades in the electronics industry, there are standard procedures recognized worldwide for the evaluation of quality and long term reliability. Many different kinds of lead-free solder alloys and soldering processes are being investigated or developed around the world, using multiple combinations of elements like tin, silver, copper, bismuth, indium and zinc, all of which require increased temperature profiles during the soldering process. To accelerate the transition to lead-free technology, the electronics industry needs a common approach. “Today, the market is confused because there are no rules for evaluating alternative technologies. What we are doing is proposing some key ground rules that will help accelerate progress”, says Cognetti. Following detailed discussions of the individual aims and approaches of the various companies, a common definition of “lead-free” components and the test methods needed to assess factors such as solderability and reliability has been developed. The companies intend to continue their co-operation at this level while pursuing their individual research programs to find the most economically and technologically effective ways to remove lead from the electronics industry.  |
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