2.5D Silicon Photonics Interposer Flip Chip Attach (Video)

In the field of silicon photonics, advanced packaging integration is key to achieving product performance. Flip chip attach of Silicon Photonics devices poses new challenges and limitations not encountered for flip chip attach and underfill of mainstream silicon devices. The first challenge in 2.5D silicon photonics die integration is its susceptibility to cracking during downstream reflow processing. The second challenge is to keep the edge-coupling waveguide facet of the silicon photonics die uncontaminated after all MCM assembly processes, for optical coupling. The third challenge is the post-reflow flip chip standoff variation and the underfill coverage under the silicon photonics die that affect optical coupling sensitivity between the edge-coupling waveguide and the planar lightwave circuit (PLC). We have successfully demonstrated flip chip attach of silicon photonics optical light engine (OLE) on an organic substrate using both thermocompression bonding and mass reflow processes with custom tooling to achieve defect-free and uniform standoff bonding of Pb-free flip chip bumps. Various underfill control methods were explored to achieve maximum coverage and avoid underfill creeping onto the waveguide facet. Furthermore, we achieved stable optical coupling post-stress testing. More investigation would be necessary to further improve coupling efficiency stability.