Research to standardise the evaluation of silicon nitride ceramic substrates

The AIST Group and NGK INSULATORS are jointly researching validation methods for evaluating thermal diffusivity of silicon nitride ceramic substrates used for power semiconductor components and other such applications.

The research aims to develop the highest accuracy methods for evaluating cutting-edge products and foster the production and development of advanced silicon nitride substrates for manufacturers.

Silicon nitride ceramic substrates play a pivotal role in Active Metal Brazing (AMB) substrates for power modules. These substrates function as heat dissipators in power semiconductor modules. The thinner the substrate and the higher its thermal diffusivity, the greater the operational efficiency of the power semiconductor module. The rising adoption of EVs and HEVs is driving greater use of power semiconductor modules designed for high power, which, in turn, is driving demand for thinner substrates that deliver substantial thermal dissipation performance.

However, a lack of definitive methods for evaluating thermal diffusivity of substrates thinner than 0.5 millimeters has given rise to challenges for ensuring consistency of measurement results. This joint research enlists AIST and its extensive knowledge of evaluation methods along with NGK and its advanced ceramic substrate technologies in efforts to collect data to quantify the preliminary process, which affects the measurement of thermal diffusivity of substrates. This will enable the verification of methods for evaluating high-performance thin substrates that are even thinner than 0.5 millimeters, not yet defined under existing Japanese Industrial Standards (JIS), contributing to high accuracy of measurement data and future standardisation of evaluation methods.

AMB substrates for power modules comprise a silicon nitride ceramic substrate and two copper plates. The AMB circuit substrates for power semiconductor modules of NGK have proprietary advanced bonding technology to create a thin bonding layer of just a few microns or less between the ceramic substrate and copper plates. This greatly reduces thermal resistance and internal strain in the bonding layer, resulting in exceptional thermal dissipation properties.

Demand for silicon nitride has risen recnetly for use in AMB substrates for power modules due to its high thermal conductivity, exceptional insulation performance, heat and corrosion resistance, and hardness.