Now, copper connections for high-speed computing

Washington, Feb 12 : Researchers have designed copper connections for high-speed signals between computer chips.

This improved signal transmission line, made of an organic substrate for high speed computing has been developed by Graduate student Todd Spencer and Regents' professor Paul Kohl.

With computers becoming more complex, there is an increased demand for more connections between computer chips and external circuitry such as a motherboard or wireless card. Also with integrated circuits becoming more advanced, it is required that better connections that operate at higher frequencies with less loss in order to maximize their performance.

According to the researchers, improving these two types of connections will increase the amount and speed of information that can be sent throughout a computer.

Currently, the vertical connections between chips and boards are made by melting tin solder between the two pieces and adding glue to hold everything together.

The current study has demonstrated that replacing the solder ball connections with copper pillars creates stronger connections and the ability to create more connections.

"Circuitry and computer chips are made with copper lines on them, so we thought we should make the connection between the two with copper also," said Kohl.

Kohl also said that both solder and copper can tolerate misalignment between two pieces being connected, but copper is more conductive and creates a stronger bond. Thus, the researchers have developed a novel fabrication method to create all-copper connections between computer chips and external circuitry.

For the study, firstly the researchers electroplated a bump of copper onto the surface of both pieces. Then, a solid copper connection between the two bumps is formed by electroless plating, involving several simultaneous reactions occurring in an aqueous solution without the use of external electrical current.

The pillar, which is the same thickness as a dollar bill, is fragile at room temperature. Thus, the researchers anneal it, or heat it in an oven for almost an hour to remove defects and generate a strong solid copper piece.

It was found that strong bonds were formed at an annealing temperature of 180 degrees Celsius.

In addition to this new method for making vertical connections between chips and external circuitry, Kohl is also developing an improved signal transmission line with the help of graduate student Todd Spencer.

Kohl presented his work in these areas at the Materials Research Society fall meeting.

ANI