Session: K16-02: HEAT TRANSFER IN ELECTRONIC EQUIPMENT II

Paper Number: 131827

131827 - An Embedded Microfluidic Approach for Direct Cooling of Copper Windings in Printed Circuit Boards 

Abstract: 

Increasing the current density of phase windings is a means to increase the torque density, and thus the power density, of an electric machine. Furthermore, recent demonstrations of planar inductors within printed circuit boards (PCB) have demonstrated coil current densities that exceed those achievable in traditional power-dense machinery. In view of these application needs, this study explores an approach to push the envelope of achievable current densities in copper windings on PCBs to >50 A/mm² using direct liquid cooling. This is enabled by fabricating multi-layer PCB stacks having embedded internal microchannels for microfluidic cooling with a dielectric fluid that is in direct contact with internal copper winding traces. Prototype PCB stacks are custom-made such that there are ~100s micron height fluid microchannels that follow the geometry of the winding trace. The PCB stack layers are fabricated by etching the copper winding trace pattern into copper clad laminate (FR-4) sheets using a patterned film to apply etch resist and placing the sheet in a ferric chloride etch solution. The backside of the laminate is machined to create the microchannels and form an internal manifold feature to direct the coolant flow. The individual sheets are aligned and sealed together using transfer tape to form the stack.  Thermal characterization of the prototype stack is performed using an experimental flow loop facility with liquid HFE-7100 as the working fluid. The experimental facility controls the inlet flow rate and temperature of the fluid entering the PCB test section.  The inlet temperature is set at 25 ˚ C, subcooled significantly below the saturation temperature to ensure single-phase operation. A calibration is performed to characterize the temperature-dependent electrical resistance of the copper trace. With this resistance calibration, the electrical current and voltage drop across the winding can be measured in- situ to infer the winding electrical resistance during experiments, using the calibration to correlate to a given temperature of the winding. This measurement allows for characterization of temperature rise of the winding under direct cooling as a function of current density.  

Presenting Author: Daniel Moguel Purdue University

Presenting Author Biography: Daniel Moguel received his Bachelor of Science degree in mechanical engineering at Washington State University. He is now a PhD student under the guidance of Dr. Weibel at Purdue University.

Authors:

Daniel Moguel Purdue University
Steven Pekarek Purdue University
Justin Weibel Purdue University