|Through Wafer Interconnection (TWI) is a first level interconnection method to inter-connect electrical signal of two stacked dies directly through the silicon. The interconnection is formed with micro-bumps connecting with through silicon vias (TSV). The bonding process can be conducted in either die-to-wafer (DtW) format or wafer-to-wafer (WtW) format.
The idea was proposed more than 20 years ago and early work can be tracked back to 1990s. Recently, TWI has become an increasingly more critical technology. Application as well as production of this technology for memory stacking and CMOS Image Sensor (CIS) has commenced in recent years.
TWI comprises TSV technology, double side redistribution layer (RDL) and micro-bumping technology. It provides the advantages of a) shortest signal connection path, thus reducing signal loss and increasing performance; b) Lower power consumption; c) Package size, form factor miniaturization and d) Heterogeneous integration capability. Additionally, the front-end-of-line (FEOL) scaling down has reached the area close to physical limit that it starts to depart from Moore's Law, and the alternative solution from 3D IC stacking become very promising and the major driving force of TWI.
Applications of TWI mainly focus in 2.5DIC (Si interposer integration) , 3D active die stack and Wafer-Level MEMS (WLMEMS).