HFE7500 Coolant Dielectric Strength Augmentation Under Convective Conditions

Power densification and rising module heat losses cannot be managed by traditional “external-to-case” cooling solutions. This is especially pronounced in high voltage systems, where intervening layers of insulating material between the power devices and cooling solution need to be sufficiently thick to provide adequate voltage isolation. As operating voltages increase, the required thicknesses for these insulating layers become so large that they limit the ability to extract the heat. A direct cooling approach that addresses voltage separation issues represents a unique opportunity to deliver coolant to the hottest regions, while opening up the opportunity for increased scaling of power electronics modules. However technical concerns about long-term performance of coolants and their voltage isolation characteristics coupled with integration challenges impede adoption. Here, the reliability and performance of a dielectric fluid of the hydrofluoroether type, HFE7500, are examined to advance the feasibility of a direct cooling approach for improved thermal management of high-voltage, high-power module. The breakdown voltage of the dielectric fluid is characterized through relevant temperatures, flow rates, and electric fields with the ultimate goal of developing design rules for direct integrated cooling schemes.