I'll Take Mine Unleaded
Veteran audio reviewer Martin Colloms and I were taking a preprandial walk across London's Hampstead Heath, following Cream's reunion concerts at the Royal Albert Hall last May. Martin was getting animated:
"And don't ask about the whiskers!"
Of course, I had to ask about the whiskers.
Martin was telling me about some listening tests he had performed on two identical samples of an amplifieridentical, that is, except that one had its components attached to its printed circuit board with conventional solder and the other with lead-free solder.
Normal solder is an alloy of tin and lead (silver is sometimes added), which has the unusual property of melting at a lower temperature than either metal on its own. The commonly used SN63 (63% tin, 37% lead) melts at 183°C (361°F) compared with 327°C (621°F) for lead and 232°C (450°F) for tin. This temperature is low enough and the soldering time short enough that there is not much in the way of potential damage to the components being joined, which is one reason why tin-lead solders are ubiquitous in the manufacturer of consumer electronics products.
However, the metal lead is extremely toxic, which is why its use in domestic water pipes, plumbing solders, gasoline, paint, fishing weights, gun shot, etc., has increasingly been abandoned. Now it is time for manufacturers of electronic products to give up using it, at least in Europe, where the EU's Restriction of Hazardous Substances in Waste Electrical and the Electronic Equipment Directive (RoHS for short) mandates the exclusive use of lead-free solders in products on sale to European consumers after July 1, 2006. The related Waste Electrical and Electronic Equipment Directive (WEEE), set to take full effect in Europe in 2008, will require manufacturers to take back products for free and to recycle 65% percent of their average weight. (For a guide to this subject, see www.pb-free.info/laymans_terms.htm.)
To give some context, the 6 million metric tons (6 billion kilograms) of electrical and electronic waste disposed of in Europe in 1998 included 27,000 metric tons of lead and 8 metric tons of mercury (AEA Technology figures). The lead used to shield the CRTs in computer monitors is of particular concern because it is in a soluble oxide form that is readily leached from landfills. Which is presumably why, according to Collapse, Jared Diamond's recent book on why human societies disappear, such computer waste is now a major export from the US to China.
I don't think anyone would argue with the need to eliminate lead from the environment, both from newly manufactured products and waste electronics. But achieving the desired goals in either field will not be easy. A 2002 article in Spectrum, the IEEE's excellent monthly magazine, examines the difficulty of eliminating lead from electronics waste. Changing to the use of lead-free solders also presents manufacturers with problems, not the least of which is the higher temperatures required to form a connection than with lead-tin solder. For example, solder alloyed from tin, silver, and copper melts at between 206°C and 227°C, depending on the ratios of the metals and the presence of other elements such as antimony and bismuth. These higher temperatures will stress the electronic components being soldered significantly more than lead-tin's melting point does, and possibly affect long-term reliability.
And, as Martin said, there are the "whiskers" to contend with. Apparently, not only are solder joints made with lead-free solders more brittle, they are prone to sprout single-crystal tin whiskers. Given the very high component density typical of modern surface-mount construction, these whiskers can make unwanted electrical connections, again with an adverse effect on long-term reliability.
At the time of writing it remained unclear, despite much Googling, what the US intends to do in these areas, though California's Electronic Waste Recycling Act of 2003 (SB20), which came into effect this summer, establishes standards and fees for the collection and recycling of certain electronic wastes. But given that: a) Japan appears to be moving faster toward eliminating lead from their products than is Europe; b) Europe's RoHS directive appears to affect products designed and manufactured before the July 2006 implementation date; and c) the WEEE directive places the responsibility for the costs of recycling and disposal of products on manufacturers, it would appear that the American high-end audio industry is facing a sea change in how it does business.
Unless it stops doing business outside the US. Which would be a tragedy, not the least because the American high-end audio industry has addressed a global market from the outset.
Originally published in the August 2005 Stereophile eNewsletter.