Low temperature Cu-Cu bonding by sintering Cu nanoparticles for power electronics

Student thesis: Doctoral ThesisDoctor of Philosophy


Sintered Cu interconnection for power electronics has attracted considerable interest recently. Cu nanoparticles are promising interconnection material due to low cost and superior conductivity while they readily oxidize and need special processing and storing conditions. To solve these problems, a specific in situ reduction-sintering of both CuO and Cu nanoparticles by glycerol was developed in this thesis. The proposed method produces high sintered Cu joint strength of over 20 MPa but without the need for pressurized sintering or protective gas atmospheres. Meanwhile, this thesis employs a quasi-in-situ method combining scanning electron microscopy (SEM) observation and ion beam etching to investigate the mechanism of grain growth and twin formation in the bulk sintered Cu nanoparticle structure during sintering. A novel strengthening mechanism of grain boundary (GB) shifting which eliminates the high porosity bonding interface was found. The effect of sintering conditions on the grain and pore size, porosity and strength of the sintered Cu structure and the micro-fracture mechanism of the joint were investigated. Finally, this thesis investigates the reliability of sintered Cu joint by in situ reduction-sintering process under high temperature aging in air. The complex oxidation effect on the microstructure and strength of sintered Cu structure was unraveled. Kirkendall void (K-void), a typical defect in solder alloys, is found to form along the GBs in the bulk sintered Cu during aging and results in a degradation of joint strength.
Date of Award1 Nov 2022
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorSamjid Mannan (Supervisor) & Mark Green (Supervisor)

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