Most power module designs today are based on ceramics made of aluminum oxide (Al2O3) or AlN, but as performance requirements rise, designers are looking into other substrates. In EV applications, for example, switching losses go down by 10% when the chip temperature goes from 150°C to 200°C. In addition, new packaging technologies such as solder-free modules and wire-bond-free modules make the existing substrates the weakest link.
Another important factor is that the product needs to last longer in harsh conditions, like those found in wind turbines. The estimated lifetime of wind turbines under all environmental conditions is fifteen years, prompting the designers of this application to seek out superior substrate technologies.
Increasing utilization of SiC components is a third factor driving enhanced substrate alternatives. In comparison to conventional modules, the first SiC modules with optimal packaging demonstrated a loss reduction of 40 to 70 percent, but also demonstrated the necessity for innovative packaging techniques, including Si3N4 substrates. All of these tendencies will limit the future function of traditional Al2O3 and AlN substrates, whereas substrates based on Si3N4 will be the material of choice for future high-performance power modules.
Silicon nitride (Si3N4) is well-suited for power electronic substrates due to its superior bending strength, high fracture toughness, and high thermal conductivity. The features of the ceramic and a comparison of critical variables, such as partial discharge or crack formation, have a major effect on the final substrate behavior, such as heat conductivity and thermal cycling behavior.
Thermal conductivity, bending strength, and fracture toughness are the most important properties when selecting insulating materials for power modules. High thermal conductivity is essential for the rapid dissipation of heat in a power module. The bending strength is important for how the ceramic substrate is handled and used during the packaging process, while the fracture toughness is important for figuring out how reliable it will be.
Low thermal conductivity and low mechanical values characterize Al2O3 (96%). However, the thermal conductivity of 24 W/mK is adequate for the majority of standard industrial applications of the present day. AlN's high thermal conductivity of 180 W/mK is its greatest advantage, despite its moderate reliability. This is the result of Al2O3's low fracture toughness and comparable bending strength.
The increasing demand for greater dependability led to recent advancements in ZTA (zirconia toughened alumina) ceramics. These ceramics have significantly greater bending strength and fracture toughness than other materials. Unfortunately, the thermal conductivity of ZTA ceramics is comparable to that of standard Al2O3; as a result, their use in high-power applications with the highest power densities is restricted.
While Si3N4 combines excellent thermal conductivity and mechanical performance. The thermal conductivity can be specified at 90 W/mK, and its fracture toughness is the highest among the compared ceramics. These characteristics suggest that Si3N4 will exhibit the highest reliability as a metalized substrate.
