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Intel, Carnegie Mellon Develop RF-Activated 'Green' Nano-Solder
| 2010-01-21 |
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A new method for soldering circuit boards not only will be more environmentally friendly, but it will speed up the manufacturing process and improve the integrity of the electrical interconnection.Intel and Carnegie Mellon University have developed tuned magnetic nanoparticles that mix with environmentally friendly solders which can be heated with radio frequency signals, thereby substituting a green room temperature process for the environmentally unfriendly high-temperature solder reflow process used today.
CMU received Intel funding for a project "using magnetic nanoparticles in the radio frequency heating, melting and reflow of solder for microelectronics circuits," said Michael McHenry, the CMU professor of materials science and engineering who collaborated on the project with Intel Senior Packaging Materials Engineer Raja Swaminathan. The research group—which included doctoral candidates AshFague Habib and Kelsey Miller and undergraduate student Matt Ondeck—presented its results at this week's Magnetism and Magnetics Materials Conference (Jan. 18-22, 2010, Washington, D.C.).
Integrated circuits—from Intel microprocessors to Micron memory chips—are connected together on a printed circuit board with solder made molten all at once, allowing it to reflow over the entire connected circuit. As it cools, the solder solidifies into a single massive interconnection that holds all the integrated circuits in perfect electrical contact with each other for the lifetime of the device.
Unfortunately, soldering circuit boards is one of the most environmentally unfriendly processes in electronic device manufacturing, and one that has gotten worse instead of better in recent years, due to the high melting temperature of environmentally friendly solders.
Lead-free solder mandates forced manufacturers to switch to lead-free formulations, most of which had to be reflowed at higher temperatures than lead solders. As a result, chip warpage has gotten worse in recent years, resulting in lower yields during manufacturing and higher failure rates in the field. CMU and Intel's new RF soldering technique, on the other hand, does not significantly heat a chip's entire package, but only locally heats its metal leads—resulting in almost no warpage, thereby improving both manufacturing yields and the prospect of fewer in-field failures.
Today, the conventional method of solder reflowing requires pulling populated circuit boards off the assembly line and baking them with either hot-air convection or an infrared oven. CMU's green process, on the other hand, removes the need for the baking step by mixing magnetic nanoparticles into the soldering paste, and just passing boards through an RF coil to melt the solder. This cuts the energy required to reflow solder in an oven and turns the baking step into just another room-temperature assembly line process.
Intel cautioned, however, that several engineering refinements need to be made before the new RF soldering method can be used commercially.
But if it ends up working as advertised, others will have to also resort to RF soldering procedures to remain competitive, since it not only speeds up the manufacturing process by moving soldering onto the line, but it also improves the integrity of the electrical interconnection itself.
Funding for this project was also supplied by the National Science Foundation.
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