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Design for Manufacture: A Tale of Two Materials
November 20, 2013 |Estimated reading time: 1 minute
Since the turn of the 21st century, there has been intensive research toward the development of embedded optical channels for transporting high-speed digital signals within printed circuit boards. I suspect that an alternative to copper traces might be commercially viable by 2035 or sooner, depending on the development of semiconductor devices with integrated photonics to transmit and receive signals through those channels.
The development of the optical waveguides and integrated photonics is driven largely by the capacity demands (as well as the power consumption) of high-performance routers and network switches, whose backplanes may span more than 20 inches. Signal attenuation due to dielectric and conductor losses is a major concern for designers of those backplanes, as are signal reflections caused by impedance variations resulting from shifts in the dielectric constant of laminates with frequency. Signal propagation delay, which is governed mostly by laminate dielectric constant, and trace crosstalk are also spurring the development of optical channels.
Optical channels would be immune from noise, virtually lossless, and electrically independent of surrounding material. They would be the conduit for high-speed signals, while copper traces elsewhere in the boards would comprise the remainder of circuits. However, creating those channels involves changes throughout the entire infrastructure of electronics manufacturing, including semiconductor materials and fabrication processes, IC and PCB design tools, and IC packaging technology, beyond the development of optical materials compatible with high-volume, panel-based PCB manufacturing processes. That will take time. Meanwhile, PCB materials with stable Df values on the order of 0.003 up to at least 10 GHz are necessary to meet channel loss budgets in such current high-speed digital applications as network line cards for 40 Gbit/s and faster data rates.Read the full column here.Editor's Note: This column originally appeared in the October 2013 issue of The PCB Design Magazine.