Double-sided IPEM cooling using miniature heat pipes

Abstract

Integrated power electronic module (IPEM) planar interconnect technologies offer opportunities for improved thermal management by allowing thermal access to the upper side of the power devices. In this paper, the feasibility of using miniature heat pipes to achieve effective double-sided cooling is investigated by analyzing the complete thermal circuit associated with the power device. A nominal case was modeled using the ANSYS(tm) finite element software in a single-sided and double-sided configuration. The numerical model predicted that the double-sided configuration would result in a 13/spl deg/C reduction in the maximum temperature compared to the single-sided case, for the same 100 W/cm/sup 2/ power dissipation in the semiconductor die. This corresponds to a 15% decrease in the maximum temperature rise relative to ambient or a similar increase in allowable power dissipation. Twenty-eight percent of the heat was removed from the upper side of the IPEM in the double-sided case. An additional benefit associated with double-sided cooling was a significant reduction in the spatial temperature gradients along the surface of the IPEM which would translate to lower thermally induced stress and higher reliability. The sensitivity of the numerical predictions to important parameters; including the dielectric conductivity, contact conductance, and heat sink characteristics are numerically investigated. An experimental fixture was fabricated and used to measure a miniature rectangular heat pipe's performance characteristics and the solder joint resistance at its evaporator and condenser interfaces in order to validate the numerical model inputs and demonstrate the required heat pipe capacity. The tested heat pipe was limited to approximately 80 W/cm/sup 2/ heat flux in a vertical, evaporator-over-condenser orientation. This limit was not observed in a vertical, gravity-assisted orientation for applied heat flux up to 125 W/cm/sup 2/. Equivalent heat pipe resistances of approximately 0.12 and 0.08 K/W were measured in these orientations, respectively. The contact resistance of the indium solder joint was measured and found to be approximately 0.1 cm/sup 2//spl middot/K/W.