Fabrication of Polyimide/Aluminum Nitride Composites and Wafer Channel Filling via Direct Ink Writing.

The emergence of three-dimensional heterogeneous integration (3D HI) has pushed forward the development of chip-to-wafer (C2W) hybrid bonding technology. To mitigate stress concentration during thermal annealing and wafer thinning processes of C2W bonding, a direct ink writing (DIW)-based 3D printing approach was proposed to fill the channel between two adjacent chips on the bonded wafer (i.e., wafer channels). A composite slurry consisting of polyimide (PI) as base material and aluminum nitride (AlN) nanoparticles as fillers was prepared. Through surface chemical modification and ultrasonic treatment, the slurry featured uniform filler dispersion (with particle size less than 1 μm) and adequate viscosity (3327 mPa·s), which fits the 3D printing process. The cured film demonstrated superior thermal stability and mechanical properties compared with pure PI, with a coefficient of thermal expansion (CTE) of 4.97 ppm/K, which matched that of silicon-based materials and exhibited excellent bonding. This approach provides a cost-effective and efficient alternative to chemical vapor deposition (CVD) techniques for filling wafer channels.