Unglamorous solder is the foundation for all appliances

Working in what was once described to him as the "proctology of Electrical Engineering," Mark Palmer, of Kettering, is making researching solder alloys a lot sexier than it used to be.

"I had a dean who described solder as the proctology of electrical engineering because everyone thinks its unattractive to work with and when it doesn't work right it's a pain in the appropriate place," said Palmer, assistant professor of Industrial and Manufacturing Engineering and Business. "But there is a lot of good science to come out of solder research and a lot of good opportunities for Kettering students. While solving real engineering problems, we can potentially make several scientific discoveries," he said.

What most people don't realize is that every electrical appliance from toasters to computers relies on solder. More specifically, lead-tin solder alloy. "Lead-tin solder has been the alloy of choice for solder material for well over 100, maybe 1,000 years," said Palmer. "It is one of the most well known, well characterized alloys, and everything has been designed around it, and the temperature at which it melts." So the un-sexy solder is the foundation for electrified life as we know it.

The problem with lead-tin solder is found in health and safety concerns related to lead. There is pressure from Japan and European countries to completely ban lead from consumer products, so a lead-free solder alloy alternative is being sought world-wide.

Palmer is currently researching sintering and thermal fatigue of solder in an attempt to help find an alternative. So far "the vast majority of lead-free alternatives melt about 100 degrees hotter than the traditional lead-tin solder," he said, "that would destroy most electronic components."

Sintering is a process typically used to make solid parts from the powders of high melting temperature materials. Sintering can be used to make solder joints from lead-free solder paste without melting the solder, thus reducing the processing temperature. "And those joints are stronger than those made by melting the normal lead-tin solder," said Palmer. "We're in the process of testing it thanks to an $85,000 grant from the National Science Foundation to investigate the sintering of solder joints," he said.

In addition to reducing the processing temperature, sintering solder paste will reduce the amount organic materials that are needed to form a good joint. Solder needs fluxes (organic cleaners) to eat away oxide so it will join to another substance. The chemical reaction where the oxide is removed often produces a conductive or corrosive residue as a by-product. These residues used to be removed with Chlorofluorocarbons or CFC's, which have been banned from use because they were environmentally unsafe.

Palmer will start thermal fatigue research in October to better understand how solder fails in electrical appliances that are constantly turned on and off. The research is funded by a $114,000 NSF grant.

Thermal fatigue relates to how solder expands as it is heated. "Solder expands more than metal it is adhered to," said Palmer, "whenever you turn on an electrical appliance you are heating the solder up to a very high fraction of its melting point. Even at room temp it's at 60-70 percent of its melting point. The material undergoes thermal (temperature) induced fatigue, which is just like bending a paper clip, except it's induced by turning the appliance on and off," he said.

The bigger problem is the properties in that material change with exposure to a high temperature, so as it's exposed, it's not only being stressed, it is being weakened. "There are so many complicated interactions that no one has accurately modeled them," said Palmer, "what we are going to do is try to identify some easier measured-material properties that can correlate to thermal fatigue resistance, develop an empirical model and then verify it. It will be based on how much energy is absorbed and dissipated by the joint.

"Right now the problem with qualifying a solder is no one understands how these joints fail at these temperatures," said Palmer. "For years we only had one solder alloy and no one cared about its micro-structural features. Now that we are trying to get lead out of solder, people are in the position that they have to qualify these materials. What we are trying to develop is a plan to get a good scientific understanding of the process so that people can make intelligent material selection choices from a variety of alloys," he said.

The solder alloys used in his research have been used to help make materials science easier for other instructors to introduce to students. Using support from a $15,000 NSF CCLI Grant, Palmer published an article in the June 2002 issue of the Journal of Metals outlining simple experiments that can be done in a traditional two-hour lab period. "The experiment I laid out in the JOM shows how we could use an alloy system to enhance education," said Palmer. "It fell out of the work on lead-free solder, it was actually one of the lead-free alternatives. Other instructors can take the information and re-construct the experiments," he said. The JOM publishes about 50 to 60 articles a year, but not many about education, he said.

He has already requested funds from NSF for his next project - developing a ceramics testing laboratory at Kettering. "The plan is to have seniors design equipment for undergraduate labs," Palmer said. "In order to test ceramics, you have to bend them and we don't have that apparatus. Currently its much too expensive to buy, so the idea is to make something cheap so we can bend the ceramics, measure the load, and measure how far it goes," he said.

"I enjoy working at Kettering," said Palmer, "I like being able to do engineering while discovering science and have that balance." Originally from Cos Cob, Conn., a town his ancestors first settled in the 1630's or 40's, Palmer currently lives in Flushing, Mich.

Written by: Dawn Hibbard
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