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Professor Paul Kohl and two of his graduate students have developed methods to create all-copper connections between computer chips and external circuitry and to link signals between chips to increase the amount and speed of information that can be sent throughout a computer.
Kohl is the Thomas L. Gossage chair and Regents professor in the School of Chemical and Biomolecular Engineering.
The vertical connections between chips and boards are currently formed by melting tin solder between the two pieces and adding glue to hold everything together. Kohl's research shows that replacing the solder ball connections with copper pillars creates stronger connections and the ability to create more connections.
The pillar is the same thickness as a dollar bill. The researchers anneal it, or heat it in an oven, for an hour to remove defects and generate a strong solid copper piece.
"I've also studied the optimal shape for the connections so that they're flexible and mechanically reliable yet still have good electrical properties so that we can transmit these high-frequency signals without noise," said graduate student Tyler Osborn.
The researchers have been working with Texas Instruments, Intel and Applied Materials to perfect and test their technology. Jim Meindl, director of Georgia Tech's Microelectronics Research Center and professor in the School of Electrical and Computer Engineering, and Sue Ann Allen, professor in the School of Chemical and Biomolecular Engineering, have collaborated on the work.
In addition to this new method for making vertical connections between chips and external circuitry, Kohl also is developing an improved signal transmission line with the help of graduate student Todd Spencer.
"Several very long communication pathways exist inside a computer that require a very high performance electrical line that can transmit at higher frequencies over long distances," Spencer said.
Kohl and Spencer also have developed a new way to link high-speed signals between chips using an organic substrate. The researchers are designing a coaxial cable for this chip-to-chip signal link that should greatly increase the maximum signal frequency the connection can carry.
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