When metals such as tin, zinc and cadmium are placed under mechanical stress, one way the stress is relieved is by the sprouting of tiny threads or sticks of metal called whiskers. The whiskers are thinner than a human hair and can “grow” over a period of months or years at a rate of up to a millimeter a year. Most are less than a millimeter in length. The distance between electronic components is often very small. The gaps may be small enough for the tiny whiskers to bridge them and cause unintentional shorts and equipment failures. At frequencies above 6GHz or in fast digital circuits, the whiskers also can act as miniature antennas, affecting the circuit impedance and causing reflections. The whisker problem was first identified in the late 1940s, and soon after it was determined that adding lead to tin plating and solder mitigated the issue. Until fairly recently, the standard solder mixture for electronics work was 60% tin and 40% lead. Other ingredients have also been added to the alloy for specific purposes, like the rosin placed in some solders to remove impurities from the solder joint while soldering. Despite its advantageous properties, lead has also been linked to serious health concerns. Consequently, efforts have been made to remove lead from as many products as possible, including solder. But until a suitable substitute for lead is developed, problems with solder whiskers are likely to continue. In the aerospace industry, whiskers have grown in pure tin-plated electromagnetic relays, with expensive results. In one example, both the primary and backup processors on the $250 million Galaxy IV geostationary communications satellite were rendered inoperative by whisker growth. The satellite was responsible for carrying millions of pager signals, as well as the broadcast feeds for the NPR and CBS networks, and had been in service for only a few years when it failed in 1998. Millions of tin whiskers were found during an inspection of the space shuttle Endeavor , due to the use of pure tin-coated clamps to hold circuit boards in place. The electronics were made in the 1980s, before NASA adopted its current rule requiring a small amount of lead in its tin coatings. A chronicle of documented tin whisker-induced failures can be found on the NASA website at [url”>http://nepp.nasa.gov/whisker/failures/index.htm . In 2003, the EU enacted a directive called Reduction of Hazardous Substances (RoHS), which stated that by 2006, most electronic products made or sold within the EU could not contain more than a very small amount of lead, cadmium, mercury and a few other hazardous chemicals. Similar measures are being considered or are already in place in other countries, including Japan , China , South Korea , Argentina , Australia and the United States . Due to the high cost of maintaining separate production lines, many electronics manufacturers have already gone lead-free and converted to producing RoHS-compliant materials. So even though the U.S. has not instituted a policy concerning lead or other hazardous chemicals in electronic components, it may soon become difficult to purchase solder and other electronic components containing lead. The only commonly available RoHS-compliant solder contains about 96% tin and 2% silver, and costs about 50% more than lead-bearing solder. It’s not known whether solder joints made with RoHS-compliant solder will suffer from whisker growth problems. Consider the current uncertainties regarding the future of lead in solder in this country, then review the comparison of crimped vs. soldered electrical connections in last month’s column. After that, I hope you’ll be convinced that crimped electrical connections are the way to go in the majority of automotive situations. News source: Motor