The study of 20-μm-pitch interconnection interconnection technology of 3D packaging focused on reliability, ultrasonic flip-chip bonding and Cu bump bonding are described. The interconnection life under temperature cycling test was acceptable level as semiconductor packages. Failure analysis and finite element analysis elucidated the effect of material properties. The accuracy of ultrasonic flip-chip bonding was almost same level as the thermo compression bonding and the electrical connection was also confirmed. Atomic level bonding was established at the interface of the bumps. As for Cu bump bonding, dry process was applied for UBM removal. Electroless Sn diffusion in Cu was investigated and clarified that the intermetallic was formed just after plating. Finally, we succeeded to build a stacked module with 20-μm-pitch interconnection.