A $360,000 award from the National Science Foundation will team Binghamton University researchers Eric Cotts and Daryl Santos with researchers at Universal Instruments on a project that could prove critical to the survival and growth of the US electronics industry.
With Japan and Europe poised to move to lead-free electronics assembly within the decade, US electronics manufacturers will be forced to follow suit to maintain marketplace viability, said Peter Borgesen, a project manager at Universal Instruments. In microelectronics, lead-tin solder is the material traditionally used to join the chip or integrated circuit to the board. The Environmental Protection Agency calls lead “a highly toxic metal.” It has been linked to a range of health effects, from behavioral problems and learning disabilities, to seizures and death.
“In principle, there’s a health concern, and we need to replace something (lead-based solder) that may eventually be outlawed,” Borgesen agreed. “But we may not be up against a law so much as we will be up against the public perception,” he added.
“Somebody’s going to start selling green products, and if we can’t, we’ll be in trouble.”
While the pressure to move to lead-free microelectronics assembly opens “a huge can of worms” for electronics manufacturers, it is a windfall from the perspective of fundamental research, according to Eric Cotts, professor of physics and co-director of Binghamton’s materials science program.
“If you’re a metallurgist or a condensed matter physicist or a materials scientist, it’s a great challenge,” Cotts said. “You had a problem that was essentially solved. Everyone thought they understood what was going on, and now there’s another huge can of worms and a lot of interesting science.”
That’s because while most of the major questions regarding the physical properties and behavioral characteristics of traditional lead-tin alloys have been answered, the basic science behind the five most promising lead-free alloys-all of which are some combination of tin, silver and/or copper-is wide open.
“Five year ago, if you talked to somebody in the United States about replacing lead-tin they would have told you there was no way,” Cotts said. “It melts at 183-degrees Celsius, and the whole industry is married to that temperature range.”
By comparison, it takes temperatures about 35 degrees higher to melt tin-silver-copper alloys.
“That’s a huge change for the manufacturer,” Cotts said, “because when you melt the solder, you have to heat the whole substrate to well above that temperature and there are a lot of different components now exposed to those conditions.”
Forsaking the reliability, predictability and manageability of lead-tin solder isn’t a choice US electronics manufacturers come to with enthusiasm, Borgesen said.
“It’s certainly not a matter of trading up,” he said. “It’s not an improvement from a technical perspective. In fact, we’re very lucky if it’s only a small step back.”
Even the basic chemistry of lead-tin made it easier for researchers to predict how it would react, Cotts agreed. While lead helps to lower the melting point and enhanced the flow of lead-tin solder, it is essentially inert and did not take part in the actual joining between the metal and the solder, he said. That meant fewer variables to affect the process.
To the contrary, in proposed replacements such as tin-silver-copper, silver and copper react with the tin to form intermetallic compounds, Cotts said.
“Furthermore, they can diffuse very rapidly in tin so even though they’re present in small concentrations, they’re completely capable of participating in and significantly altering reactions at the interface between the solder and the metal,” he said.
Such uncharted variables mean high anxiety for electronics manufacturers for whom the ability to make a priori quantitative predictions about assembly yields and reliability might be more important than to their counterparts in any other industry, Borgesen said.
“If you build bridges, you build one bridge every 10 years,” he said. That production rate allows plenty of time to check and double check every operation.
“But electronics manufacturing involves enormous numbers of the same product coming off assembly lines,” Borgesen said. “We need an in-depth understanding of the issues and of the technologies and of the materials. We need to be able predict things and have good faith in our predictions without being able to check them very often. That means we need fundamental research.”
All of which is where Binghamton University becomes a windfall to Universal Instruments, he said.
“We need the University as a resource-for students, who work with us in our laboratory and are a substantial part of our research program, and for the scientific support of the faculty, through whom we can link to truly fundamental academic research of the sort Professor Cotts will be conducting,” Borgesen said.
“We need to have a link to that. We need more than just some papers here and there. We need to be able to go over and talk to them. We need to go over and ask them questions. We need to interact and provide feedback to them. It’s very important not only that this work is going on over there. It’s important that it’s local to us, and we can have a very intense daily dialogue with them.”
Cotts who studies atomic transport and mass transfer in thin film metal systems, said he looks forward to working with Santos, an associate professor of systems science and industrial engineering, and Borgesen. After exploring the evolution of the microstructure of lead-free solders through different melting and annealing heat treatments, Cotts expects to collaborate with researchers conducing a related Semiconductor Research Corporation grant on campus. That second phase collaboration would allow researchers to look at how the microstructure of alloys affects their mechanical properties.