Date of Graduation

12-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Electrical Engineering

Advisor/Mentor

Zhong Chen

Committee Member

Alan Mantooth

Second Committee Member

Yue Zhao

Third Committee Member

Jia Di

Keywords

Power module prototype, Nano-diamond composites, Power conversion, Thermal performance, Switching performance

Abstract

The objective of this dissertation research is to develop a novel three-dimensional (3-D) wire bondless power module package for silicon carbide (SiC) power devices to achieve a low parasitic inductance and an improved thermal performance. A half-bridge module consisting of 900-V SiC MOSFETs is realized to minimize stray parasitic inductance as well as to provide both vertical and horizontal cooling paths to maximize heat dissipation. The proposed 3-D power module package was designed, simulated, fabricated and tested. In this module, low temperature co-fired ceramic (LTCC) substrate with vias is utilized as an interposer of which both top and bottom sides are used as die attachment surfaces, the SiC MOSFET bare dies are flip-chip attached on the LTCC interposer using nickel-plated copper balls, high horizontally thermal conductive material is integrated into the LTCC interposer to improve its thermal dissipation capability. Hence, the LTCC interposer provides both electrical and thermal routing and the nickel-plated copper balls replace bond wires in conventional planar power module as the electrical interconnections for the SiC power devices. On the other side, direct bond copper (DBC) substrate are used at both top and bottom sides of the 3-D module to achieve electrical path for SiC devices and double-sided cooling. As a result, 3D power routing is achieved to reduce stray inductance, and both vertical and lateral paths are utilized to spread heat generated by the power devices in this compact module architecture.

Electrical simulation was performed to extract the parasitic inductances in the 3-D package and compared to other reported module packages. Low loop parasitic inductance of 4.5nH at a frequency of 1MHz is achieved after optimization. Thermal and thermo-mechanical simulations were also conducted to evaluate the thermal performance and mechanical stress of the proposed module structure.

The fabrication process flow of the 3-D wire bondless module is developed and presented. The fabricated half-bridge module was evaluated experimentally by double-pulse test and thermal cycling test. Significant reduction in voltage overshoot and ringing was observed during the double-pulse test, and the module shows no degradation after thermal cycling test.

To push the double-sided wire-bondless module to higher voltage application, a 3.3-kV SiC double-sided wire-bondless common source module was designed, fabricated, and tested. Electric field simulations were performed considering the associated challenge of increased electric field strength in the higher-voltage wire-bondless module. High voltage blocking test was added to evaluate the high voltage operation capability as well.

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