Lead-free Solder Licensed Worldwide as EU Rules Take Effect
March 6, 2006
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As a result of the
Waste Electrical and Electronic Equipment (WEEE) and the
Restriction of Hazardous Substances (RoHS) directives, the European Union (EU) will strictly limit the amount of lead and other hazardous materials within the circuitry of any electronic appliance sold, beginning July 1.
Though a computer's circuit boards contain only small amounts of lead solder, the problem is overall volume. By some estimates, about 3,000 tons of electronic waste end up in U.S. landfills each day.
Given the global nature of the electronics industry, the European ban is truly international in scope. As electronics and appliance manufacturers scramble to meet the new restrictions, a lead-free solder developed at the U.S. Department of Energy's Ames Laboratory is playing a key role in compliance.
Composed of lead and tin, traditional solder melts and flows easily, but sets up quickly to create a strong, durable bond between the mating surfaces. A solder blend of 63% tin and 37% lead results in a eutectic alloy - one that acts like a pure metal with a single melting (and solidification) point.
"Finding a substitute for lead that gave the solder similar properties was difficult," said Ames Laboratory senior metallurgist Iver Anderson. "With our basic understanding of alloys, we developed a tin-silver-copper alloy that offered a lower melting temperature and greater strength than other lead-free alternatives being considered."
The Ames Laboratory's solder technology was patented in 1996 and more than 60 companies worldwide have licensed the lead-free solder, according to Ken Kirkland, executive director of the Iowa State University Research Foundation (ISURF).
"With the European directives and a similar commercial initiative in Japan, we’ve seen a growing interest in the alloy," Kirkland said. "The technology was a little ahead of its time, but it's an excellent product and we have a strong patent; you can't ask for a better combination than that."
The Ames Lab solder is just one of several lead-free alternatives on the market. The type and specific composition of lead-free solder also depends on the soldering technique used and the end application. In addition to the tin-silver-copper alloy, Anderson's group developed modified alloys that also contained iron, cobalt and other similar elements. This blend is suitable for higher temperature applications.
According to experts, an ongoing problem with today's lead-free alternatives is their tendency to get brittle after repeated or prolonged heating cycles. As technological advances have boosted operating temperatures, heat has become an issue. For example, the steady climb in computer processor speeds has meant a corresponding increase in the amount of heat they generate. And computers aren't the only devices that generate heat.
"Even the circuitry in your cell phone operates at about 125 degrees centigrade," Anderson said. "Over six months' use, that can mean several hundred hours of high temperatures. If you drop it, the solder joints have become more brittle and the risk of it breaking is higher."
To combat this solder "aging" problem, Anderson's group looked for more additives for the tin-silver-copper formula, including silicon, titanium, chromium, manganese, nickel, zinc and germanium. Joints soldered with the different alloys were subjected to 150 C for 1,000 hours, then tested for both shear strength and impact strength.
"Zinc appears to be most attractive in terms of retained ductility and strength and also offers benefits in terms of solderability, ease of alloying and material cost," Anderson said.
As an aside, another benefit of this recent work is the development of a simple technique for characterizing the bulk composition of solder joints using an electron microprobe. This permitted Anderson's research team to analyze new compositions being studied under different soldering conditions.
"With the elimination of lead, tin-silver-copper solders are here for the long run," Anderson said. "But that doesn’t mean we'll stop trying to improve our basic understanding of how these alloys work in order to improve their performance."
Source: Ames Laboratory.