Researchers fashion copper for high-speed computing

As computers and networks gain complexity one thing is always needed: more speed. With that axiom in mind, researchers today said they have developed a fabrication method to create all-copper connections between computer chips and external circuitry, significantly boosting the speed and amount of data that can be sent throughout a computer.

Solder and copper can both tolerate misalignment between two pieces being connected, but copper is more conductive and creates a stronger bond, researchers said Georgia Tech School of Chemical and Biomolecular Engineering researchers. 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. Replacing the solder ball connections with copper pillars creates stronger connections and the ability to create more connections, researchers said.

In addition to this new method for making vertical connections between chips and external circuitry, researchers are also developing an improved signal transmission line. This is especially important in high-performance servers and routers where inter-chip distances can be large and signal strength may be significantly degraded.

In a release the researchers described how they make the new technology: The researchers first electroplate a bump of copper onto the surface of both pieces, a process that uses electrical current to coat an electrically conductive object with metal. Then, a solid copper connection between the two bumps is formed by electroless plating, which involves several simultaneous reactions that occur in an aqueous solution without the use of external electrical current.

Since the pillar, which is the same thickness as a dollar bill, is fragile at room temperature, the researchers heat it in an oven for an hour to remove defects and generate a strong solid copper piece. They found that strong bonds were formed at an annealing temperature of 180 degrees Celsius. The researchers have also been investigating how misalignments between the two copper bumps affect pillar strength.

The researchers have been working with Texas Instruments, Intel and Applied Materials to perfect and test their technology. Funding for the project is coming from the Interconnect Focus Center, one of the Semiconductor Research Corporation/Defense Advanced Research Projects Agency (DARPA) Focus Center Research Programs.

Vendors and researchers are looking at all manner of chip technology to speed computers or even make the whole process of developing chips more efficient. For example IBM recently announced a semiconductor wafer reclamation process that removes chip circuitry with an abrasive pad and water, saving money and leaving the silicon in better shape for reuse in solar panels or other duties. Enabling reuse is crucial because IBM estimates that approximately three million silicon wafers worldwide are scrapped each year by the semiconductor industry - representing a significant solar recycling opportunity.

Meanwhile, NASA researchers last year said they designed and built a new circuit chip that can take the heat of a blast furnace and keep on performing. Silicon Carbide chips can operate in 600 degrees Celsius or 1,112 degrees Fahrenheit where conventional silicon-based electronics - limited to about 350 C - would fail.

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