Glass panel based packaging: optical waveguides for data transport in large packages

High performance computing is a main driver to bring glass as a stiff substrate to panel-level packaging. A main reason for choosing glass are the challenges that arise by increasing package sizes beyond 100 mm × 100 mm: a very high manufacturing accuracy is needed to achieve structure sizes of less than 2 μm width in the electrical redistribution lines of the package. Having a transparent material like glass in the core of the packaging also gives the opportunity to include optical waveguides into the package. The main advantage of optical data transport is the low loss in comparison to any electronic data transport. For data rates of several hundred GBit/s one can easily gain a factor of 100 in loss by switching from the electric domain to an optical waveguide. In the present work we investigate different possibilities of optical waveguides in glass. These include laser‑written waveguides, waveguides by ion exchange and filled trenches obtained via reactive ion etching (RIE). We focus on solutions for glasses which are already used today for glass panel‑based packaging. Since the multidisciplinary field of packaging tackles multiple challenges simultaneously, a special focus is on the best compromise between thermomechanical properties, mechanic reliability, electrical performance, and efficient optical waveguides.