https://www.rutronik.com/ BETTER COOLING PERFORMANCE 13 www.power-mag.com Issue 2 2025 Power Electronics Europe reduced, thereby improving the performance, reliability, and service life of the component. To ensure effective component performance, continuous advancements in both MOSFET and package technology are essential. The new OptiMOS-MOSFETs in an SSO10T package serve as a prime example of this (Fig. 1). In the OptiMOS6 series for 40 V (Fig. 2) and OptiMOS7 series for 80 V (Fig. 3), both featuring an SSO10T package, the dies are contacted in a plane manner using copper clips rather than thin wires. This method ensures excellent thermal and electrical connection between the chip and the package. Heat is mainly dissipated via a contact surface on the top-side of the package. Thermal interface material (TIM) can be used for the thermal connection to a cooling surface. These films or pastes level out any unevenness and roughness of the surfaces. Depending on the material, the films also provide electrical isolation between the component and the cooling surface. Rutronik stocks thermal interface materials, e.g. from Fischer Elektronik and Innotape. High power density – even in limited installation spaces The advantages of the top-side cooling of MOSFETs are many. In addition to an increase in overall efficiency, more compact designs are possible. This approach allows the thermal flow resulting from the power loss of the MOSFETs to be transferred directly from the component surface to a cooling surface or heat sink. There is no longer a need for diversion through the printed circuit board. This helps reduce the thermal resistance between the MOSFET and the heat sink. The printed circuit board can thus be less complex. Thermal vias and the insulated metal substrate (IMS) embedded in the PCB, which otherwise reduce the heat resistance of the printed circuit board, are no longer needed. The effective heat dissipation enhances thermal impedance by 20 to 50 percent (Fig. 4), which boosts the operating temperature range or enables the components to achieve greater performance at the same operating temperature. The design also supports higher application currents, which can replace larger packages and provide additional space savings, for example. Topside cooling in combination with the OptiMOS 40 V family enables higher power densities, which is crucial in applications with limited installation space. Furthermore, the Infineon SSO10T package is listed as LHDSO-10 JEDEC, which makes it easier to interchange with components from other suppliers. The availability of second sources is a key selection criterion, enhancing the customer’s supply assurance for the placement location on the PCB. Typical automotive applications for topside cooling MOSFETs are electric power steering, electric brakes, power distributors, and electric auxiliary drives. The design allows for a thermally optimized mechanical construction, resulting in higher power densities and system-level savings. Other suppliers offering MOSFETs with topside cooling include, e.g., Vishay and Toshiba. Figure 3: Infineon’s product portfolio for 80 V MOSFETs of the OptiMOS 7 series with an SSO10T package (source: Infineon) Figure 4: Comparison of thermal impedance across pulse durations with various thermal coupling methods: Depending on the material and thickness of the thermal interface, the thermal resistance is reduced by 20 to 50 percent (left). Design of the top-side cooling (right) (source: Infineon) www.power-mag.com
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