PhD Defence Lei Wang | Thermo-mechanical Design of Heterogeneous Integrated Wide Bandgap Power Modules

Thermo-mechanical Design of Heterogeneous Integrated Wide Bandgap Power Modules

Lei Wang is a PhD student in the Department of Power Electronics. (Co)Promotors are dr.ir. R.J.E. Hueting and prof.dr.ir. G. Rietveld from the Faculty of Electrical Engineering, Mathematics and Computer Science and dr. W. Wang from Yongjiang Laboratory.

Wide bandgap (WBG) semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) offer higher switching speed, greater power density, and elevated operational temperature capabilities compared to silicon-based counterparts. However, conventional packaging technologies cannot fully leverage these benefits, necessitating innovative packaging strategies. This dissertation explores pressure contact technology (PCT) to enhance performance and reliability of highly integrated WBG power modules. Various interconnection approaches are evaluated for their suitability: fuzz buttons provide low parasitic inductance and flexibility for gate connections; graphene film (GF) elastomers offer compact size and high thermal conductivity; and metal sheet springs ensure robust power interconnections. A novel spring connector with low inductance (3 nH) and electrical resistance (5 ) is utilized to connect substrates, enhancing heat dissipation and mechanical stability. The electro-thermal characteristics and reliability of pressure contact with molybdenum plates (PCMo) technology are compared with emerging die-attach technologies such as pressureless sintered Ag (SAg), pressure sintered Cu (PSCu), and commercial TO220 counterparts incorporating the same SiC chips. Experimental results demonstrate that PCMo introduces additional contact resistance (∼10 , 0.42 K/W) but exhibits superior power cycling reliability (∼ 6053 cycles) under a junction temperature from 50  to 200  due to the elimination of die-attach failures. Failure analysis identifies degradation and crack mechanisms in SAg, PSCu, and TO220 samples. Building on these insights, a 3D PCT-based half-bridge SiC module is developed using GF and fuzz buttons, achieving a low thermal resistance of 0.66 K/W, minimal parasitic inductance of 5.1 nH, and reduced voltage overshoot of 5.8%. For high-power applications, an eight-chip parallel SiC module with metal sheet springs demonstrates balanced current distribution and low inductance of 4.8 nH. The findings of this dissertation highlight the potential of PCT in improving the performance and reliability of heterogeneous integrated WBG power modules, particularly for high-power and high-temperature applications.