High density metal-metal interconnect bonding with pre-applied fluxing underfill

The results of initial investigations incorporating a fluxing wafer level underfill (WAUF) into a Cu/Sn-Cu intermetallic bonded device are presented. The studies were performed utilizing a 640 × 512 high density area array test vehicle (10⁵ interconnects/cm²). The fluxing pre-applied wafer level underfill was integrated into a solid-liquid diffusion bonding process which achieved an interconnect yield of 99.99%. Bond formation, underfill encapsulation, and electrical yield were evaluated using several imaging techniques and electrical testing. These results and results from reliability testing of the primary sample set are presented.