Session: 10-01 Interactive Presentations

Paper Number: 100340

100340 - Combined Voltage Shielding Capacity of Dielectric Fluids and Dielectric Surface Coatings 

High-power electronic systems will be needed to drive the increasing electrification of mobility, the shift from hydraulic and pneumatic actuation to electric power as well as the proliferation of renewable energy generation. One way to enable more power is through the development of modules that operate at higher voltages, which has been made possible by the advent of wide band gap (WBG) semiconductor devices with voltage ratings exceeding 1.2 kV. Additionally, these WBG devices deliver low drain-source on resistance (RDSon) capabilities, enabling high amperage power modules that further increase power density; however, packaging, and cooling techniques are struggling to keep up. To meet the demands of increased power density, new advancements in packaging materials, packaging architectures and thermal management have emerged. Novel cooling solutions that have been explored include those aimed at increasing the heat transfer area through microchannel flow passages, novel fluid delivery methods via sprays or jets for enhanced heat transfer rates and cooling uniformity as well as two-phase flow to exploit the latent heat of boiling. A common theme for all these efforts is the minimization of the convective thermal resistance (R_conv), which still leaves a large component of the overall thermal resistance, specifically junction-case resistance (R_jc), largely untouched. In high voltage systems in particular, the intervening layers of insulating material between the power devices and cooling solution need to be sufficiently thick to provide adequate voltage isolation further increasing R_jc and resulting in diminishing cooling returns with lower R_conv. Direct/integrated cooling approaches that bypasses these thermally inefficient layers represent an opportunity to meet cooling demands in these high power, high voltage modules.

While direct cooling has been demonstrated for low voltage applications, concerns over voltage isolation has impeded adoption in high voltage applications. To overcome this challenge, this study leverages a combination of dielectric fluids and dielectric coatings to enable the implementation of thermal management closer to the power devices. The voltage shielding capacity of fluorinated coolants, specifically HFE7500 and FC3283, along with that of Parylene-C-based conformal surface coatings are explored. Both voltage blocking technologies demonstrated an ability to maintain good voltage blocking capacity even when exposed to field strengths exceeding 16.8kV/mm in the case of the dielectric fluids and 33.5 kV/mm for 2µm-thick layers of Parylene C.  To potentially improve voltage blocking characteristics while minimizing thermal resistance, this study also explores the combined voltage shielding capacity of HFE7500 coupled with thin Parylene C coatings deposited via chemical vapor deposition (CVD). The tests are conducted on point-point electrodes coated with a 10μm film of this coating to shed more understanding on the combined voltage blocking capacity of the coating and fluid. Learnings from this effort can help guide the safe implementation of direct cooling and unlock the increased scaling of power electronics.

Presenting Author: Ange Christian Iradukunda University of Arkansas