Optical PCB components
Research groups around the world have been working to develop ways of integrating optical transmission into printed circuit boards (PCBs). However, the majority of solutions are elaborate, expensive, and rarely suitable for mass production. Dr. Ruth Houbertz-Krauß of the Fraunhofer Institute for Silicate Research ISC in Würzburg has found a viable solution. “It is based on ORMOCER®s, a class of material that was developed at our institute,” she explains. “They are excellent, low-loss light-guiding materials, and can also be employed in PCB processes.” To create optical waveguides in a circuit board out of the viscous raw material, Dr. Houbertz modified the composition of a specific ORMOCER® system to meet the requirements of the two-photon absorption (TPA) process used to write 3-D microstructures directly in the material. What does this process consist of? “First, a 0.3-millimeter layer of the ORMORCER® material is deposited on the circuit board, on which the opto-electronic components have already been mounted. This optical coating is then patterned in the layer volume between the opto-electronic components, using a focused femtosecond laser,” says Dr. Houbertz. “The treated area has a higher refractive index than the surrounding material. It thus serves as the core of the waveguide linking the two components. The outer focal regions are not exposed, having a lower refractive index and thus acting as a cladding layer. In a subsequent process step at an elevated temperature and pressure commonly used in PCB production, the cladding layer’s refractive index is fixed. The new process reduces the number of process steps, but its real advantage lies in the fact that the optical connections are fully integrated in the optical film. There is no need for any complicated assembly between the optical and electronic components in PCBs, because the waveguides are ‘written’ right up to the edge of the pre-configured components. Together with its research partners, PCB manufacturer AT&S Austria Technologie & Systemtechnik Aktiengesellschaft, Joanneum Research GmbH and others, the ISC has demonstrated this functionality. The next step involves developing a suitable TPA system for prototype production. The aim is to be able to produce opto-electronic circuit boards with data transmission rates exceeding 4 gigabits per second. Dr. Ruth Houbertz was awarded the 2007 Joseph von Fraunhofer Prize for this work. In its assessment, the jury particularly emphasized that this world-unique manufacturing process gives AT&S a significant development lead that will allow the company to secure a competitive edge with respect to the material, technology, and production.
Paesi
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