SMAFTI package with planarized multilayer interconnects

A hybrid multilayer interconnect process and high-throughput die-to-wafer bonding technology were developed and introduced into the SMAFTI (SMArt chip connection with FeedThrough Interposer) package. The fine circuit layer FeedThrough Interposer (FTI) was fabricated between memory and logic dice and offers superior power/signal integrity, allowing over a thousand 3-D inter-chip connections through ultra-fine-pitch feedthrough vias. The unique fabrication processes of the multilayer FTI include a multilayer buildup process on a silicon wafer, filling in vias on the photosensitive polyimide layer, and planarization by chemical mechanical polishing (CMP), resulting in low production costs and an extremely flat surface that ensures void-free die bonding. A simultaneous metal/adhesive bonding process was also evaluated for high-throughput die-to-wafer bonding. Furthermore, the fine interconnect structure was verified to be fundamentally reliable.