In recent years, we have begun to see broadband semiconductors, such as silicon carbide (SiC), adopted in electric vehicle inverters to replace typical silicon insulated-gate bipolar transistors (Si IGBTs). The use of SiC allows power modules to have higher density and operate at higher temperatures, opening up new thermal and materials management opportunities for vehicle power electronics.
The transition to the SiC
Despite the rising cost of SiC metal-oxide-semiconductor field-effect transistors (MOSFETs), their penetration into the electric vehicle market has been considerable. According to research by IDTechEx, in 2020, SiC MOSFET inverters accounted for nearly 30% of the global EV market. Tesla started the trend in 2018, and others like BYD have vehicles on the road. Giants such as Stellantis and Hyundai are including SiC power electronics in lower-end models to help enable their high-voltage (800V) platforms.
Challenges of thermal management
Power electronics in electric vehicles present interesting thermal management challenges, and the adoption of SiC changes several aspects of module and package design, along with material selection. In a traditional power electronics package, several potential failure points occur with thermal cycling. As the package heats up and cools down, the mismatch in thermal expansion between the materials causes degradation of various connections, including wire splices, die junctions, and substrate junctions. In SiC packages, power density and operating temperature can be significantly increased, meaning that some traditional options are no longer suitable.
Today, aluminum wire splices are the dominant interconnect technology; however, they are a common point of failure. This has led to increased use of wire splices with aluminum alloys, copper, or even direct lead bonding. The materials used to attach the arrays are also critical. This is typically done with traditional soldering, but at higher operating temperatures (especially with SiC), standard SAC (tin-silver-copper) soldering can be unreliable, leading to the emergence of alternatives such as silver sintering to offer significantly better performance under thermal cycling. STMicroelectronics' Tesla package uses a combination of copper ribbon splices and silver-sintered aluminum wire splices for its attachment to the array. We are very interested in these emerging alternative technologies. As we move forward, we are sure to see greater adoption of these options in inverter packages to enable higher reliability in smaller form factors with increased efficiency.
On a larger scale, much like many electric vehicle batteries, vehicle power electronics tend to be liquid-cooled. Typically, the coolant flows through the fins of the heat sink located beneath the module. While this aspect of power electronics thermal management may not be as innovative as emerging materials within the package, it still presents interesting opportunities for whole-vehicle integration. Many vehicles utilize the same cooling pathway through the power electronics and electric motor. For example, in some models, waste heat can be extracted from the powertrain to heat the passenger compartment, helping to reduce losses and improve the vehicle's overall range, particularly in cold conditions.
The evolution of power electronics, particularly toward wideband semiconductors, is transforming thermal management and, consequently, the materials landscape in electric vehicle power electronics. IDTechEx's "Thermal Management for Electric Vehicles 2021-2031" report covers various use cases within electric vehicle power electronics packages, as well as investigating trends in wire splicing, die fixing, and substrate materials. Beyond power electronics, the report delves into thermal management strategies for batteries, motors, and power electronics, including market forecasts through 2031.
