Micro-Metal Bonding Technology for LSI Package

Au-Sn and Au-Ag bonding processes were developed by applying a micro-bonding process for LSI packages. An Au-plated Cu lead was bonded by a termo-compression bonding method on a Sn- or Ag-plated Cu frame using a bonding tool. The junctions were processed at a high temperature of 150°C for up to 1000h after bonding. Bonding strengths were subsequently evaluated by a 90° peeling test. As a result, Au-Sn bonding strengths were from 3 to 4.5N/mm and slightly dependent on the bonding pressure. For the Au-Ag junctions, on the other hand, these strengths were from 2 to 9N/mm and dependent on the bonding pressure. The Au-Sn and Au-Ag strengths after thermal aging were substantially the same as the initial strengths. With the Au-Sn junction, the bonding layer composed of Au, Sn and Cu, was formed. The thicknesses of the bonding layers which were made at 50MPa and 100MPa were about 2μm and 1μm, respectively. In the Au-Ag junctions, no bonding layer was formed on the interface. The unbonded area was formed at the Au-Ag interface at low pressure bonding. On the other hand, when the bonding was made at a high pressure of 150MPa, the bonding strengths were high because of no unbonded area.