This study introduces a newly developed pressure type Cu sinter paste as a joining material substituting for Ag and our investigation into its joining properties and reliability. The Cu sinter paste we developed as a filler by using low temperature sinterable copper particles was able to be sintered at 280°C from 5 to 20 minutes. Pressure was below 10 MPa under N2 atmosphere. The result of bonding strength showed high shear strength over 50 MPa between the dummy die and Ag/Cu substrate. The cohesive shear modes were shown between the Ag plated layer on the dummy die and Cu paste indicating good enough strength for initial joint reliability. The image of Scanning Acoustic Tomograph also indicated good joining layer with no voids. Ag metallized SiC-SBD and Cu bared TO-247 leadframes were bonded with copper pastes. The sound acoustic analysis was also compared with before and after joint area of Cu paste. Reliability tests showed good performance with these packages. The details will be discussed in this study.