Material synthesis routes for thin film bonding interfaces in reworkable and bumpless nano-interconnects

This work explores novel material synthesis routes towards reworkable nano-dimensional interfaces for IC-package assembly, leading to bumpless and nano interconnections. Reworkability is addressed by a thin interface of lead-free high-strength solders. Two approaches, sol-gel process and electroless plating, were used to achieve these nano-dimensional bonding interfaces. In the sol-gel process, metal-organic polymer solutions were heat-treated in a reducing atmosphere at 400°C to form lead-free solders (Sn-Ag-Cu). In the electroless plating approach, lead-free alloy films were deposited from aqueous plating solutions consisting of suitable metal salts and reducing agents. This process was done at a temperature of 45°C. The lead-free solder composition was controlled by altering the plating bath formulation. Solder films formed from both the above approaches were demonstrated to bond copper pads. Solution-derived nano-solder technology is an attractive low-cost method for bumpless nano-interconnects and other applications such as MEMS hermetic packaging and compliant interconnect bonding.