At the heart of all electronic devices and computers lie chips and electronic circuits that gain in complexity almost by the day. To keep up with the demand for faster technology, these components need to be designed for ever higher speed and performance.
They must also accommodate and enhance the multitude of connections between themselves and external circuitry. Currently, all computer chips and circuits incorporate copper layers and wires within them to conduct signals due to copper's excellent conductivity, which allows for smaller components and higher performance.
Currently, the connections between the circuit boards and chips are achieved through molten solder and glue to hold them. However, Frost & Sullivan has taken note of work being conducted by researchers at the Georgia Institute of Technology. The researchers have replaced the solder ball connections between the chip and board with pillars made of copper. The aim of this new technique is to address the increasing needs for more connections between the computer chips and external circuits and more efficient performance at very high frequencies in components such as motherboards and wireless cards.
The researchers have found that while copper offers excellent conductivity, comparable to or better than solder, it also has the ability to create stronger connections, and more of them. Copper can also tolerate issues of misalignment between the connecting pieces such as solder.
The process of incorporating copper starts with electroplating a layer of copper on the surface of the chip and board. The process essentially consists of coating an electrically conductive section with a layer of metal utilising current. The copper layers on the chip and board are then joined together by a solid copper connection through the use of electro-less plating. This process occurs when many chemical reactions occur simultaneously in an aqueous solution without the aid of external current.
To ensure that the thin copper pillar is strong enough, it is annealed to eliminate any defects and make it tough. The annealing process also gave researchers insight into the relation between the strength of the bonds and the annealing temperature, where a temperature of 180°C was found to give good results.
Apart from this, researchers also determined optimal shapes to ensure good flexibility and conductivity, especially at high frequencies. They are still investigating the relation between copper layer misalignments and pillar strength, and are also working on improving the signal transmission characteristics, which is essential for efficient long distance transmission of signals in computers.
The research to develop this new fabrication method was funded by the Semiconductor Research Corporation of North Carolina. Apart from this, the refinements and testing of the fabrication technology is being conducted through the researchers' collaboration with Intel, Texas Instruments, and Applied Materials. The technology has great potential to satisfy the demands of companies involved in electronic chip design, packaging and manufacturing and also electronic device developers and manufacturers.
For more information contact Patrick Cairns, Frost & Sullivan, +27 (0)21 680 3274, [email protected]
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