Silicon Nitride Substrates for Improved Performance in Power Electronics

Today’s power module designs are primarily based on aluminum oxide (Al2O3) or AlN ceramic, but increasing performance demands are causing designers to consider advanced substrate alternatives. One example is seen in xEV applications where an increase in the chip temperature from 150°C to 200°C reduces switching losses by 10%. Additionally, new packaging technologies like solder and wire-bond-free modules are making the current substrates the weak link.

Another significant driver of special importance is the need for an increased lifetime under harsh conditions such as with wind turbines. Wind turbines have an expected lifetime of 15 years without failure under all environmental conditions, causing designers of this application to look for improved substrate technologies as well.

A third driver for improved substrate options is the emerging use of SiC components. The first modules using SiC and optimized packaging showed a loss reduction of between 40 to 70 % compared to traditional modules but also presented the need for new packaging methods, including Si3N4 substrates. All these trends will limit the future role of traditional Al2O3 and AlN substrates, while substrates based on Si3N4 will be the designer’s choice for high-performance power modules in the future.

The excellent bending strength, high fracture toughness, and good thermal conductivity make silicon nitride (Si3Ni4) well suited for power electronic substrates. The characteristics of the ceramic and a detailed comparison of key values like partial discharge or crack growth show a significant influence on the final substrate behavior like heat conductivity and thermal cycling behavior.