Another advantage of polymer, and especially of silicone, is its flexibility, since space is often limited. Like other flexible electronics, a flexible waveguide material lets the connections be folded and wrapped around to fit the form factor. It also makes cutting and drilling the material possible without chipping it.
The Dow/IBM silicone material has losses as low as 0.03 dB/cm, which could enable links of greater than 1m. That means a link of this material could not only connect chips on the same board, but also connect two chips on different daughter cards across a backplane. It proved to be stable for more than 2,000 hours exposed to the standard test of 85C operating temperatures and 85 percent humidity, as well as during lead-free solder reflow tests of 260C.
Although the engineers now are designing boards for supercomputers and high-speed networking equipment, the same issues will eventually, and inevitably, migrate down to PCs. Polymer optical waveguides may be first placed outside the rigid PC board. But once they're accepted as a reliable technology in the field, the ultimate vision is integrating them within the rigid board, said Jones.
"Because of very high connection density and the ability to fabricate in-plane crossovers with optical waveguides, not possible with copper, you can replace several copper layers with one optical layer while increasing the performance of the system and adding value to the PC board," said Jones. "If you could replace six layers of a 16-layer board with one optical layer, the copper element of the board could come down in cost by a factor of four or five."