A method of "chemical flip-chip bonding" without loading and heating for ultra-fine chip-to-substrate interconnects

A method of chemical flip-chip bonding by electroless deposition process was proposed. This method positively utilizes preferential bridge deposition between metal pads in electroless Ni-B deposition and enables bump-less interconnect without loading and/or heating at lower temperature (60°C). Details of the deposition behavior for interconnection were investigated using fundamental test chips. The selection not only of various dimensions of pad design and pad-to-pad configurations but also of materials of base materials, was very important to achieve preferential bridge connection. Preferential bridge connections show high electric resistance because of using high resistivity materials with thin thickness. In the investigation of chip-to-substrate bonding, the low resistance interconnection could be achieved with combination usage of preferential bridge deposition and conventional electroless Au deposition from non-cyanide bath. The electric resistance of the interconnection decreased to less than one-20th, dramatically.