Sintering Cu Bonding Paste: Cycle Reliability and Applications

We have developed three Cu bonding pastes that can be sintered by three different processes. The first is a Cu bonding paste that can be sintered without the application of pressure. The adherend can be Cu, Ni, Au, Ag, or Pd and a temperature above 225 deg C is required. A hydrogen environment is necessary throughout the sintering process. The maximum bondable chip size is 7 mm x 7 mm on a Cu plate and 10 mm x 10 mm square on a direct bonded Cu (DBC) or active metal brazed Cu (AMC) substrate. The second Cu paste can be sintered by the heat press process, in which a nitrogen environment can be used and chips up to 13 mm x 13 mm can be bonded at a pressure of 5 MPa or greater and a temperature of 250 deg C or above. The third paste can be used when the diameter of the bonding region is less than 150 micrometer; here, sintering under formic acid, without the application of pressure, can be used. In this case, the adherend can be Cu, Au, Ag, or Pd.