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Self-Patterning of Silica/Epoxy Nanocomposite Underfill by Tailored Hydrophilic-Superhydrophobic Surfaces for 3D Integrated Circuit (IC) Stacking.

As microelectronics are trending toward smaller packages and integrated circuit (IC) stacks nowadays, underfill, the polymer composite filled in between the IC chip and the substrate, becomes increasingly important for interconnection reliability. However, traditional underfills cannot meet the requirements for low-profile and fine pitch in high density IC stacking packages. Post-applied underfills have difficulties in flowing into the small gaps between the chip and the substrate, while pre-applied underfills face filler entrapment at bond pads. In this report, we present a self-patterning underfilling technology that uses selective wetting of underfill on Cu bond pads and Si3N4 passivation via surface energy engineering. This novel process, fully compatible with the conventional underfilling process, eliminates the issue of filler entrapment in typical pre-applied underfilling process, enabling high density and fine pitch IC die bonding.