12 BETTER COOLING PERFORMANCE https://www.rutronik.com/ Issue 2 2025 Power Electronics Europe www.power-mag.com Better cooling performance in a compact design Author: Ralf Hickl, Product Sales Manager in the Automotive Business Unit (ABU) at Rutronik For effective component performance, continuous advancements in both MOSFET and package technology are essential. The new OptiMOS series in the SSO10T package is a robust solution for optimizing performance and reliability. According to Infineon, more than 120 MOSFETs will be installed in every passenger car with a combustion engine by 2025 [1]. Key drivers of growth are legislation in CO2 reduction, the expansion of driver assistance systems, and applications aimed at enhancing occupant comfort. Reasons enough for suppliers to increase their production capacities and advance MOSFET technology. Package and semiconductor chip determine the properties of MOSFETs The properties of a packaged MOSFET are determined both by the package and the MOSFET die, i.e. the actual semiconductor chip. The overall electrical resistance of the component is the combination of the RDS(on) of the die (chip) and the electrical resistance of the package connection. The smaller the RDS(on) of the MOSFET die, the greater the percentage of the electrical resistance of the package connection in relation to the overall resistance. The respective spice models provide an indication of the distribution of the overall resistance between the actual RDS(on) of the chip and the power resistance of the package. The spice models of Infineon MOSFETs are generally unencrypted and available on the home page. As soon as current flows through the component, conductivity losses arise according to the following equation: Ptot = I 2 x RDS(on) The resulting heat must be dissipated into the environment. This requires the lowest possible thermal resistance RthJA between the die and the outer surface of the package. Efficient cooling is crucial for performance and reliability In the automotive industry, MOSFET dies are frequently engineered to withstand high temperatures and harsh environments, ensuring they meet the demands of vehicle operation. Nevertheless, cooling the MOSFETs is crucial for performance and reliability. This is often accomplished through the use of highly conductive materials, optimized heat sink designs, and efficient heat dissipation methods. Top-side cooling is ideal for automotive MOSFETs, as the active components that generate heat during operation are situated on top of the chip. Effective top-side cooling can be achieved using thermal pastes, thermal films, heat sinks, and various other thermal solutions. By dissipating heat from the top-side of the MOSFET, the operating temperature is Figure 1: The SSO10T 5x7 package with top-side cooling (source: Infineon) Figure 2: Infineon’s product portfolio for 40 V MOSFETs of the OptiMOS 6/7 series with an SSO10T package (source: Infineon)
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