Packaging strategies for 3D integration of Photonic and Electronic chips on a Glass substrate

3D printed free-form couplers and inverse tapers are two different vertical integration strategies for coupling light between a PIC and glass interposer. For the free-form coupling scheme, 5×5×0.5 mm
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dummy silicon dies are bonded to a glass substrate using solder bumps via flip-chip bonding. The gap distance between the bonded chips is controlled by the solder height based on various bond pad sizes. An array of 14×14 square gold bond pads on the silicon chip is used with the bond pad length varying from 50 μm to 105 μm in order to maintain a required height. SAC305 solder is jetted onto the bond pads and an optimization of the reflow profile is performed to achieve defect-free, and high-wetting solder bumps. For the inverse taper coupling approach, the PIC is bonded to glass using a UV-curable optical epoxy (n=1.5). The measured vertical distance falls within the 2.8 μm required Z-tolerance for evanescent coupling according to simulation.