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Yale Scientists Develop Magnetic Lead-free Solder
March 8, 2010 |Estimated reading time: 1 minute
NEW HAVEN, CT — Yale University scientists have developed a magnetic solder that can be manipulated in three dimensions and selectively heated. The alloy is tin/silver with iron additives that allow magnetic manipulation for selective heating, reflow location control, and added strength.
Ainissa Ramirez, associate professor at the Yale School of Engineering & Applied Science and lead author of the study, and her team have developed a non-toxic solder made of tin/silver containing iron particles. The iron makes the alloy much stronger than it would ordinarily be. When an external magnetic field is applied to the molten solder, these particles align themselves within the solder, making it even stronger once it again solidifies. Second, the iron overcomes the problem of tin/silver having a higher melting point than traditional lead-based solders. By subjecting the solder to an alternating magnetic field, the solder can be selectively heated. This keeps surrounding materials at safe temperatures while melting only the solder itself. Third, an external magnetic field can be used to remotely manipulate the solder, so it can be moved into hard-to-reach places, such as narrow vertical channels. This means that broken connections within devices can be “self-healed” by applying a magnetic field to melt the solder and attach the ends together.
“There is a whole range of possibilities for this new kind of solder,” Ramirez said. “In addition to helping make the fabrication of microelectronics more environmentally responsible, these new solders have the potential to solve technological challenges.”
Until now, scientists had difficulty coming up with a suitable alternative for lead-based solders that are just as strong and have a similarly low melting point, according to the Yale researchers. “We took this as an opportunity to improve solder for the environment, but we also took it as an opportunity to reexamine how to enhance solder in general,” said Ramirez. The findings appear in the March 1 Early Edition of the Proceedings of the National Academy of Sciences. Other authors of the paper include Joshua Calabro, Xu Huang and Brian Lewis, all of Yale University. This research was funded by the National Science Foundation and the Yale Institute for Nanoscience and Quantum Engineering (YINQE).
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