Title page for ETD etd-05012001-165030

Type of Document Master's Thesis
Author Kim, Junhyung
Author's Email Address junhkim@vpec.vt.edu
URN etd-05012001-165030
Title Analysis of Direct-Soldered Power Module / Heat Sink Thermal Interface for Electric Vehicle Applications
Degree Master of Science
Department Electrical and Computer Engineering
Advisory Committee
Advisor Name Title
Lai, Jason Committee Chair
Boroyevich, Dushan Committee Member
Chen, Dan Y. Committee Member
  • inverter and electric vehicle
  • soldering
  • thermal resistance
  • void reduction
Date of Defense 2001-04-27
Availability unrestricted
Reducing the thermal impedance between power module and heat sink is important for high-power density, low-cost inverter applications. Mounting a power module by directly soldering it onto a heat sink can significantly reduce the thermal impedance at the module / heat sink interface, as compared to the conventional method of bolting the two together with a thermal grease or some other interface materials in between. However, a soldered interface typically contains a large number of voids, which results in local hot spots. This thesis describes approaches taken to reduce voids in the solder layer through surface treatment, solder paste selection, and adjustment in solder-reflow conditions. A 15MHz scanning acoustic microscope (SAM), a non-destructive inspection tool, was used to determine the void content at the module / heat sink interface. The experimental results show that a significant reduction in thermal resistance can be achieved by reducing the void content at the soldered module / heat sink interface. Moreover, a comparison of the thermal resistances in cases using the worst soldering, which contains the largest voided area, ThermstrateTM and thermal grease are presented. Thermal performances of the modules are studied by simulation with Flotherm.
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