Stress relaxation structure using Ni nano-particle/Al micro-particle composite paste for power device packaging

Sintered metal nanoparticles are expected to replace solder as a high-temperature joining technology for power semiconductors. However, a challenge is the inability to relieve thermal stress caused by the mismatch of the coefficient of thermal expansion (CTE) between the device and the substrate. In this study, we evaluated the bonding performance of a new stress relaxation bonding structure using Al micro particles as stress relaxation material, based on the property that Ni nanoparticles and Al can bond in the atmosphere. We also verified the stress relaxation effect of an Al foil used as a stress relaxation intermediate layer for large area chips. In the sintering bonding using Ni nanoparticles, it is possible to directly bond to the Al electrode in the atmosphere. Evaluation of the joining performance and FEM analysis confirmed that the Al micro-particles and Al foil layers can be expected to have a relaxation effect on the stress generated by CTE difference.