Impact of Through Glass Vias Filling on the Performance of Passive Thermal Cooling in Photonic Packages

In this paper, we examine glass as a 2.5D interposer for next generation photonic packaging, where copper vias have been incorporated in the glass to greatly increase its thermal dissipation characteristics. The thermal performance of 110µm thick glass interposers with and without through glass copper vias (20µm diameter and 100µm pitch) as well as silicon interposer have been investigated. A temperature difference of approximately 38°C has been observed in the maximum temperature of the laser die bonded on glass with and without Through Glass Vias (TGVs). These experimental results have been compared with simulation results, which highlights the via filling factor (FF) effect on the thermal dissipation of glass with TGVs. Simulations have been conducted which show the effects of solder thickness, FF, Via Diameter, Via Pitch, glass thickness and via height on the effective thermal conductivity and maximum surface temperature of the laser die. The laser bonded on all three types of 3mm x 3mm interposers (Glass, Glass with TGVs and Silicon) has many factors affecting the heat dissipation such as thickness of gold layer plated on top of copper vias and via shape which have been explored through simulations. The experimental results act as the reference point to propose optimized design parameters. The surface interaction of thin solder preform for packaging laser dies on glass with copper vias has also been demonstrated through an EDX analysis. This analysis offers a design rule set that can then be implemented in the photonic component packaging on glass with TGV substrates.