Abstract
This paper presents thermal and electrical characterizations of an ultra-thin flexible 3YSZ (3 mol% Yttria Stabilized Zirconia) ceramic substrate to explore its potential for electronic packaging applications. The thicknesses of the ultra-thin 3YSZ substrates were 20 μm and 40 μm. The flexible thin ceramic substrate can provide not only better modulus for higher robustness in manufacturing, especially in Z-axis direction of modules, but also low thermal resistance for high density 2D (two dimensional) / 3D (three dimensional) power module packaging applications. To better understand the thermal and electrical properties of the ultra-thin flexible ceramic, different measurements were employed. Thermal conductivity was measured at different temperatures by 3-omega method, the results were verified by thermo-reflectance measurement at room temperature. Relative permittivity was measured from 100 Hz to 10 MHz, with dielectric losses determined by dielectric spectroscopy. The dielectric breakdown of the ultra-thin flexible 3YSZ was measured, from room temperature to 150 °C. Weibull analysis was performed on 20 measurements for each temperature. The test results showed that the thermal conductivity of 3YSZ decreased from 3.3 W/mK at 235 K to 2.2 W/Mk at 600 K. The relative permittivity decreased from 30.9 to 27.3 for higher frequencies for both substrates with different thickness. The temperature-dependence of relative permittivity and dielectric loss was studied. The results showed that these two parameters increased slowly from −65 °C to 150 °C, but more repidly from 175 °C to 250 °C. The dielectric breakdown decreased at higher temperature, from 5.76 kV to 2.64 kV for thickness of 20 μm, 7.84 kV to 3.36 kV for thickness of 40 μm. SEM (Scanning Electron Microscopy), EDS (Energy-dispersive X-ray Spectroscopy) and XRD (X-ray Powder Diffraction) analysis was performed to compare the microstructure of 3YSZ ultra-thin substrate and that of AlN (Aluminum Nitride) substrate. The microstructure of 3YSZ consisted of smaller round particles and that of AlN contained larger columnar particles. FEA (Finite Element Analysis) simulations were also applied to demonstrate the thermal properties of 3YSZ in simplified model of power modules. Though the measurement results showed that it did not meet expectations for high temperature power modules, the present work showed potential applications of the ultra-thin 3YSZ substrates in low voltage power modules, LED modules.
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