Si3N4 Substrates with Anisotropic Thermal Conductivity Suitable for Power Module Applications

Inhalt:
This paper demonstrates, for the first time, an original approach to improve the thermal performances of Si3N4 substrates for power module applications. In power modules, the ability to dissipate heat in the thickness direction of Si3N4 substrate is more important than that in the in-plane direction. Our idea is to achieve higher thermal conductivity of the Si3N4 substrate in the thickness direction compared to that in the in-plane direction by controlling the orientation of the β-Si3N4 grains in Si3N4 substrates. To verify this idea, several kinds of Si3N4 samples were prepared by the reaction bonding method using the same raw materials under different process conditions and evaluated by means of XRD and SEM analysis and thermal conductivity and mechanical strength measurements. It was definitely confirmed that the thermal conductivity in the thickness direction tends to improve as the number of β-Si3N4 grains oriented in the thickness direction increases, while keeping the superior mechanical strength, by controlling the preparation conditions. From these experimental results, it is expected that Si3N4 substrates prepared based on this approach exhibit excellent thermal performances in power modules.