Optimization and Characterization of Flexible Polymeric Optical Waveguide Fabrication Process for Fully Embedded Board-level Optical Interconnects

Optical interconnections on printed circuit board are promising approach for use throughout the backplane and motherboard. Optical interconnect with its low propagation loss and high data-transfer density become the key driver to solve the limitation of electrical interconnections which fail to meet with increasing data rate requirement The advantages of embedded polymer waveguide as optical interconnects is the potential compatibility with current PCB or silicon manufacturing process which could facilitate a smooth technology transition from electrical to optical technologies. This paper reports on optimization of the fabrication process of 10 cm long flexible polymer waveguide layer with 45° micro-mirror on a PI film by using soft molding to achieve fully embedded board-level optoelectronic interconnects. The photo-active UV-curable fluorinated acrylate resin with low propagation loss (0.05 dB/cm @ 830 nm), WIR30-RI series (Chemoptics) was chosen as clad and core (70 ¿m × 70 ¿m) materials, respectively. The waveguide layers are sandwiched between two polyimide films which support and protect the waveguide layer. Soft molding process is developed to replicate the polymer waveguide. It is known that oxygen inhibition is the key issue when UV-curing the acrylate coating under oxygen atmosphere. Nitrogen shielding is successfully eliminating the oxygen inhibition effect and has improved the surface condition. Scanning electron microscope (SEM) was used to analyze the effectiveness of the optimization process. The 45 micro-mirror in waveguide was formed by using 90° V-shaped diamond blade. The propagation loss of fabricated waveguide is -0.3 dB/cm at 850 nm wavelength. Detailed of each process are discussed in the paper.