Co-integration of High-Bandwidth Photonic and Electronic RDL on 2.5D Glass Interposers Using Low Optical Absorption Photoimageable Dielectric Polymer

Integration of single mode waveguides for high-bandwidth photonic interconnections and fine line RDL structures for high-bandwidth electronic interconnections on 2.5D glass interposers was demonstrated. Both structures were fabricated using the same benzocyclobutene (BCB) based low optical absorption photoimageable dielectric polymer. This material has low optical absorption, which is suitable for optical waveguides, and simulation shows that the size of the BCB based waveguide cores is close to the size of fiber cores, which enables improved fiber-to-waveguide direct coupling and reduces coupling loss due to mode mismatch. This material also has low dielectric loss, high glass transition temperature and high-temperature stability. Embedded trench RDL was developed using this material to realize fine line structures for 2.5D interposers and scale RDL beyond the limits of semi-additive process. Using one material system to fabricate both structures reduces the complexity of fabrication. This paper describes the fabrication process improvements, and the geometry characterization and analysis of electronic and photonic RDL on glass interposers.