As computers become more complex, the demand increases for more connections between computer chips and external circuitry such as a motherboard or wireless card. And as the integrated circuits become more advanced, maximizing their performance requires better connections that operate at higher frequencies with less loss.
Improving these two types of connections will increase the amount and speed of information that can be sent throughout a computer, according to Paul Kohl, Thomas L. Gossage chair and Regents’ professor in Georgia Tech’s School of Chemical and Biomolecular Engineering. Kohl presented his work in these areas at the Materials Research Society fall meeting.
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.
“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.
Solder and copper can both tolerate misalignment between two pieces being connected, according to Kohl, but copper is more conductive and creates a stronger bond.With funding from the Semiconductor Research Corporation (SRC), Kohl and graduate student Tyler Osborn have developed a novel fabrication method to create all-copper connections between computer chips and external circuitry.
Since the pillar, which is the same thickness as a dollar bill, is fragile at room temperature, the researchers anneal it, or heat it in an oven for an hour to remove defects and generate a strong solid copper piece. Osborn found that strong bonds were formed at an annealing temperature of 180 degrees Celsius. He has also been investigating how misalignments between the two copper bumps affect pillar strength.
“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 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 also collaborated on the work.
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.
“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,” explained Spencer.
This is especially important in high-performance servers and routers where inter-chip distances can be large and signal strength may be significantly degraded. Kohl and Spencer have developed a new way to link high-speed signals between chips using an organic substrate, with funding from the Interconnect Focus Center, one of the Semiconductor Research Corporation/Defense Advanced Research Projects Agency (DARPA) Focus Center Research Programs.
Fabrication begins with an epoxy fiberglass substrate with copper lines on one side. The substrate is coated with a polymer and the areas without copper lines are exposed to ultraviolet (UV) light, which disintegrates the polymer where it’s not wanted. Then, the researchers coat the substrate with another polymer that hardens when exposed to UV light. Layers of titanium and copper are added on top of each copper line. When the layered substrate is heated at 180 degrees Celsius, the first polymer layer decomposes into carbon dioxide and acetone, which diffuse out leaving an air pocket.
“The amount of electrical loss relates to the connection’s sensitivity at higher frequencies,” explained Spencer. “Just having this air pocket there reduces our signal loss greatly.”
The researchers are currently designing a coaxial cable for this chip-to-chip signal link, which should greatly increase the maximum signal frequency the connection can carry.
Companies that make computer chips and package them into a device are very interested in these technologies, said Kohl.
“If these connections can be produced at a reasonable cost, they could be very important in the future because you’re giving the customer a better product for the same cost,” said Kohl.
Abby Vogel | EurekAlert!
Construction of practical quantum computers radically simplified
05.12.2016 | University of Sussex
UT professor develops algorithm to improve online mapping of disaster areas
29.11.2016 | University of Tennessee at Knoxville
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
08.12.2016 | Materials Sciences
08.12.2016 | Materials Sciences
08.12.2016 | Physics and Astronomy