Yale develops greener solder

Until recently, virtually all solder was made from a tin-lead alloy. But because lead is a toxic substance, there is a lot of interest in trying to find a greener alternative. Recent legislation in Japan and the European Union bans the import of electronics with lead solders. But 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.

Now Ainissa Ramirez, associate professor at the Yale School of Engineering and Applied Science, and her team have developed a non-toxic solder made of tin silver and containing iron particles. Not only is using a tin-silver alloy an environmental advantage, the addition of iron particles has other benefits.

First, 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 re-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.’

The research was funded by the US National Science Foundation and the Yale Institute for Nanoscience and Quantum Engineering (YINQE).