Substrates For Power Modules Research Articles

Thickness dependence of dielectric breakdown strength for silicon nitride substrate

Silicon nitride ceramics have attracted increasing attention as insulated heat-dissipating substrates for power modules due to their high thermal conductivity and mechanical strength. However, there are very few reports on their dielectric breakdown strength, which was only evaluated for the substrates with thicknesses between 250 and 640 µm, though thinner substrates are preferable for attaining better performance of the module. In this work, dielectric breakdown of sintered silicon nitride substrates with thicknesses ranging from 285 to 15 µm was evaluated for the first time. Average breakdown strength increased from 36.38 to 103.80 kV/mm with decreasing thickness from 285 to 15 µm. It should be noted that the silicon nitride specimen had very high dielectric breakdown voltage of 1.5 kV even with a thickness as small as 15 µm.

Thermal Decouple Design of Multichip SiC Power Module With Thermal Anisotropic Graphite

Thermal design of power modules is necessary to miniaturize and ensure reliable operation of a high-density power conversion system. Miniaturization of the power module reduces the heat conduction area and increases thermal interference among the chips in the power module package. They increase the thermal resistance from the junction of the chips to the heatsink. This article designs a multichip power module with low thermal resistance using a high thermal conductive and anisotropic material graphite. The power module substrate that uses graphite as a heat spreader for a multichip power module is designed based on numerical simulation using the finite-element method to reduce the thermal resistance and thermal interference effect of the power devices on the power module substrate. The characteristics of the designed power module substrate are experimentally validated. The developed graphite power module reduces thermal interference by using its thermal anisotropy and achieves at least 8% lower thermal resistance than the conventional copper power module.

3D structure design of magnetic ferrite cores using gelcasting and pressure-less sintering process

Gelcasting is a well established process for ceramics manufacturing which recently has been proved to be successful for soft ferrites as well. This approach is particularly interesting for power electronics application in which the magnetic components (e.g. transformers and inductors) are three dimensionally integrated on the power module substrate. This paper proposes a gelcasting process adapted to make it more effective for 3D heterogeneous integration. The main novelties in this direction consist of low solid load (65wt%) and gelation without catalyst to improve casting and de-airing steps. The magnetic properties of gelcast samples are compared with commercial materials and correlated with the microstructure.

Improved resistance to thermal fatigue of active metal brazing substrates for silicon carbide power modules using tough silicon nitrides with high thermal conductivity

The effect of temperature cycling from −40 to 250 °C on active metal brazing (AMB) substrates for power modules was investigated using newly developed silicon nitride ceramics with both high thermal conductivity of 140 W m−1 K−1 and superior fracture toughness of 10.5 MPa m1/2. Other types of AMB substrates made of AlN or Si3N4 were also tested for comparison. Both visual inspection and acoustic scanning microscopy (ASM) observation of the new Si3N4-AMB substrates after 1000 cycles revealed almost no cracks. In contrast, the Si3N4-AMB substrates with lower fracture toughness experienced crack initiation beneath the corner of the copper plate. The degradation in the bending strength after 1000 cycles was negligible for the new Si3N4-AMB substrates, whereas the bending strength of the other substrates decreased gradually with each thermal cycle. The endurance of the AMB substrates to thermal fatigue could be improved significantly by employing the new tough Si3N4 with high thermal conductivity.

パワーモジュール用アルミ一体型基板の開発

パワーモジュール用アルミ一体型基板の開発

ELID grinding characteristics and surface modifying effects of aluminum nitride (AlN) ceramics

Aluminum nitride (AlN) ceramics have excellent electrical insulation and dielectric properties, a high thermal conductivity that is approximately 10 times that of alumina, as well as a thermal expansion coefficient that is close to that of Si, and so are anticipated to be used in semiconductor mounting boards, heat-dispersing substrates for power modules, and other heat-sink materials in a variety of high-added-value applications. In this research, ELID grinding was performed on AIN, and evaluated the processing characteristics and the resulting surface properties. The results indicate that final finishing using a #30,000 wheel produced an extremely smooth ground surface roughness of 0.008 μm Ra. In addition, the ELID series demonstrated a surface hardness and sliding characteristics superior to those of the polished series. This appears to be attributable to the diffusion phenomenon of the oxygen element produced by the ELID grinding.