Relationship Between the Porosity in Cu Sintered Bonding and Thermal Cycle Reliability

Abstract:
The bonding reliability of a Cu sintered die-bond is strongly influenced by the porosity of the sintered Cu. Therefore, the relationship between the bonding reliability and porosity is important to determine the sintering conditions and estimate a product’s life. Accordingly, thermal cycle tests (TCTs) were performed on test vehicles die-bonded using a Cu sintered layer with different porosities. Cu sintered diebonds with different porosities were obtained at different sintering pressures. When the sintering pressure increased from 4 to 20 MPa, the porosity of the Cu sintered layer decreased from 26 % to 15 %. The TCT was performed up to 3000 cycles with the conditions of 200 C / 15 min ⇔ - 40 C / 15 min. The test vehicles with Cu sintered die-bonds with porosities of 26 % and 21 % failed till 500 and 2500 cycles, respectively, while those with lesser porosities of 20 %, 16 %, and 15 % did not fail up to 3000 cycles. Therefore, the less porous Cu sintered die-bond had higher thermal cycle reliability. Additionally, for the same sintering pressure or porosity, the Cu sintered die-bond had superior thermal cycle reliability than the Ag sintered die-bond. After 3000 cycles of TCT, the Cu sintered bond underwent fatigue damage at the chip edge area and exhibited small point-like fatigue in all areas. In the sintered Cu layer with porosities as high as 26 % and 21 %, the small point-like fatigue expanded with the TCT and acted as the starting point of fatigue failure. The small point-like fatigue originated from the depression caused by grain boundary deformation owing to thermal stress in the underlying Cu electrode of a SiN-active metal brazing substrate (SiN-AMB).