20 μm pitch Cu-to-Cu flip-chip interconnects through Cu nanoparticles sintering

Abstract

This report demonstrates an innovative method to achieve large scale 20 μm pitch Cu-Cu direct bonding, utilizing lithographic stencil printing to transfer small-sized nano-copper (CuNPs) paste and employs a thermocompression method for CuNPs sintering to establish interconnections between copper-pillars and CuNPs bumps. Shear tests were conducted to characterize the bonding strength. High-throughput 20 μm pitch copper-to-copper direct bonding enables lower annealing temperatures for bulk- Cu to bulk-Cu bonding. Lithographic stencil printing is used to transfer the CuNPs paste, followed by sintering of the nanoparticles to establish interconnections. Shear tests and cross-section SEM were conducted to characterize the bonding strength and quality.