Copper Sintering Pastes for Die Bonding and Large-Area Bonding

Inhalt:
The operating temperature of power devices has increased owing to their small volume and weight. From this technological trend, the Cu sintering pastes are highly required to achieve bonding reliability and heat dissipation. We are developing two copper sintering pastes for die-bonding and large-area bonding. The Cu sintering paste for die-bonding has high process-ability owing to the improvement and tackiness for temporal chip fixing, fewer contaminants surrounding the chip after sintering, high stencil printability, surface roughness capability on the dried paste, and good bonding strength to the Au adherend. The bonding reliability of sintered bonds is changed by the bonding conditions because the porosity in sintered bonding is changed by the bonding condition and is related to the mechanical properties. Therefore, we perform a thermal cycle test to clarify the relationship between porosity and bonding reliability. The Cu sintering bond for large-area bonding between a power module and cooling fin has superior bonding reliability; however, the thermal cycle life is approximately 1400 cycles in ref [4]. To improve the thermal cycle life to 2000 cycles, the materials of the cooling fin were changed and the thermal cycle life was improved using the Cu-Al clad cooling fin. From the finite element method calculation, the Cu-Al clad cooling fin produced a smaller thermal strain in the Cu-sintered bonding at the large-area bonding between the power module and cooling fin.