B.J. Soller, M. Romero, J. Schmitt, D. Huitink, W. Vinson, M. Norris, T. Akintunde
Nitride Global, Inc., University of Arkansas,
United States
Keywords: advanced packaging, thermal enhancement, test methods
Summary:
As the power density of wide-bandgap (WBG) semiconductor systems continues to increase, the dielectric layers used to isolate power modules are becoming progressively thinner. Consequently, accurately characterizing the thermal properties of thin dielectric coatings—rather than the traditional thick ceramic insulators—has become essential. Thermomechanical stress and delamination at material interfaces are often driven by local temperature gradients and mismatches in thermal conductivity between the thin dielectric layer and its underlying metallic substrate. Conventional steady-state or transient laser flash methods are poorly suited for measuring the thermal conductivity of films thinner than 50 µm, especially when these films are deposited on highly conductive substrates such as copper or aluminum. To overcome this limitation, we developed a dual-loop, liquid-to-liquid heat exchange technique to determine the effective thermal conductivity of aluminum oxynitride (AlON) coatings deposited on copper microchannel substrates. In this method, a 3D-printed ABS jet-impingement cap directs a controlled liquid flow across the AlON surface, while a second fluid loop simultaneously removes heat through the copper microchannel cooler beneath it. This configuration replicates the realistic cooling conditions found in AlON-based power modules and enables simultaneous measurement of the applied heat flux and the resulting temperature gradient across the dielectric film. System design was guided by 3D conjugate computational fluid dynamics (CFD) simulations, which were used to optimize nozzle geometry, flow uniformity, and pressure drop. These simulations established calibration curves relating total heat transfer (Q) to assumed film conductivity on both the jet and cooling sides, ensuring accurate thermal analysis under various operating conditions. During experiments, matched flow conditions were maintained using independent pumps and thermocouple arrays positioned at both inlets and outlets. By comparing measured Q-values with the simulation-derived calibration curves, we extracted bounded estimates for the effective thermal conductivity of AlON films. This combined numerical–experimental method provides a physically interpretable, in-situ measure of thermal performance under dual-sided convective loading. Beyond characterization, the dual-loop framework also serves as a design tool for evaluating how film thickness, interfacial resistance, and deposition quality influence heat spreading at the module level. As AlON and related oxynitride films become key dielectric materials for next-generation power substrates—offering both high electrical isolation and superior thermal management—such methods are critical to linking material processing, device performance, and reliability modeling. Overall, this study demonstrates that liquid-to-liquid thermal exchange, coupled with high-fidelity numerical modeling, provides a practical and nondestructive alternative to traditional vacuum- or laser-based techniques for thin ceramic coatings. It establishes a foundation for routine, realistic property extraction of dielectric films and supports the broader transition toward monolithic, metal-based power packaging architectures enabled by AlON and similar materials.