Powering the Future of SiC with Advanced Top-Side Cooling
Modern power electronics applications, from inverters in electric vehicles (EVs) to industrial motor drives and high-efficiency DC-DC converters in data centres, face an unrelenting demand for higher efficiency and greater power density without compromising long-term operation. Silicon carbide (SiC) MOSFETs have become central to meeting these requirements, offering superior switching speeds, higher voltage capabilities, and lower conduction losses compared with traditional silicon devices.
However, even the most advanced semiconductors cannot deliver peak performance without effective thermal management. The package design and its cooling methodology play a critical role in system performance, influencing not only device reliability but also the efficiency, size, and cost.
Traditional PCB-based cooling packages, such as the TO-263-7 (also referred to as D2PAK-7), have long been the standard for power MOSFETs. While effective at moderate power levels, they can limit heat dissipation, constraining system performance, reducing continuous operation capability, and introducing thermal stress that affects device longevity. Therefore, alternative approaches are needed.
SiC MOSFETs and the Critical Role of Thermal Management
SiC devices enable higher switching frequencies, voltages, and efficiencies than silicon, but these same advantages increase thermal demands. As power density rises, the challenge shifts from the silicon to how effectively heat is extracted from the device. The thermal path from the junction through the package, interface material, and heatsink defines how reliably that power can be delivered.
If this path is inefficient, junction temperatures rise, switching performance degrades, and device life shortens. Engineers must therefore treat thermal management as a core design parameter, optimising package design, interface quality, and system cooling to maintain both performance and reliability.
Limitations of Conventional Bottom-Side Cooling
The TO-263-7 package is a conventional choice for SiC MOSFETs, featuring a thermal pad on the underside that interfaces with PCB copper planes to dissipate heat. While suitable for moderate power applications, this bottom-side cooling approach has intrinsic limitations that restrict more power-dense designs.
The dependence on PCB copper planes introduces greater thermal resistance in comparison to direct heatsink contact. Furthermore, with the increase in power density, uneven heat distribution can generate hot spots, thereby negatively impacting efficiency and potentially inducing localised thermal stress that may affect both the MOSFET and possibly nearby supporting components.
In practical terms, this means engineers are forced to increase the size of the cooling system, or simply accept a lower power density, constraints that complicate the design of high-performance motor drives, renewable energy converters, and especially compact EV traction inverters where system weight impacts vehicle performance.
Top-Side Cooling Advancements
Nexperia’s X.PAK devices, including the NSF040120T2A1, are available from Avnet Silica, and represent a significant evolution in SiC MOSFET thermal design. By placing the thermal pad on the top side of the device, X.PAK allows for direct thermal coupling to a heatsink via a thermal interface material (TIM). This approach eliminates the reliance on the PCB as the primary heat path, significantly improving cooling efficiency.
To demonstrate the advantages of topside cooling, Nexperia has evaluated the latest X.PAK devices against traditional TO-263-7 packaged components.
In DC/DC buck continuous operation tests, with a switching frequency of 64 kHz the X.PAK (NSF040120T2A1) reached 11.5 kW of input power, compared with 9 kW for the TO-263-7 (NSF040120D7A1) – a roughly 27% increase in power handling capability.
Furthermore, at an equivalent 7.5 kW, X.PAK exhibited a case temperature 38.8°C lower than the TO-263-7, demonstrating its superior thermal management. This enhancement in performance reduces case-to-heatsink thermal resistance by approximately 30%, enabling higher sustained power levels without compromising device reliability.
Figure 1: Input power versus case-temperature (Source: Nexperia)
These thermal advantages translate directly into system-level benefits. In EV traction inverters, lower thermal resistance supports more compact and lightweight cooling systems, improving packaging efficiency and overall vehicle energy use. In industrial motor drives, enhanced heat dissipation enables sustained high-load operation without derating, maintaining uptime and long-term reliability. Finally, in renewable energy converters, particularly those exposed to demanding ambient conditions, reduced junction and case temperatures extend device lifetime and limit the need for oversized or high-cost thermal solutions.
Figure 2: Vertical mechanical stress test results (Source: Nexperia)
Thermal and Mechanical Interface Considerations
To fully realise the benefits of X.PAK’s top-side cooling, both the TIM and the mechanical connection to the cooling element must be carefully managed. A properly applied TIM ensures efficient heat transfer by filling microscopic surface irregularities between the X.PAK drain tab and the heatsink, minimising air gaps and reducing thermal resistance.
Nexperia’s testing showed that case-to-heatsink thermal resistance can vary by up to 35-36% when using gap-filler TIMs, depending on how they are applied and compressed. Silicone-based TIMs, on the other hand, proved more consistent and stable under mechanical stress, maintaining reliable thermal contact once fully compressed.
To ensure sufficient TIM mating and long-term reliability in the field, mechanical strength is another key area Nexperia has optimised with the X.PAK range. Vertical mechanical stress investigations demonstrate that X.PAK retains full electrical and structural integrity even under forces exceeding 2300 N, with no change in electrical behaviour.
Furthermore, during mechanical evaluation, the device indicated an absence of visible damage, delamination, and defects in the device.
This inherent mechanical resilience protects the device during operation as well as during assembly, allowing designers to apply firm, repeatable mounting pressure – critical for maximising thermal coupling and overall system reliability.
Electrical Performance and dV/dt Ruggedness
In addition to thermal efficiency, X.PAK SiC MOSFETs offer improved electrical ruggedness. Rapid alterations in voltage across a MOSFET, expressed as dV/dt, may result in parasitic currents and voltage stress that compromise dependability. A high dV/dt tolerance prevents these effects, enabling faster switching and allowing engineers to fully exploit SiC’s performance advantages when combined with thoughtful package design and top-side cooling.
Figure 3: Results from the scanning acoustic microscopy (C-SAM) after compression test (Source: Nexperia)
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Powering the Shift Together with Nexperia
Each year, Nexperia introduces over 800 new types of power MOSFETs, wideband gap semiconductors, IGBTs, and analog & power management ICs, with more than 70 new parts in analog & power management released in 2024 alone.
With the ongoing shift to renewable energy and the electrification of transport and industry, the demand for higher power and greater energy efficiency in electronics is increasing. Wide bandgap technologies including SiC and GaN bring many advantages.
WBG OVERVIEWTo evaluate dV/dt ruggedness, Nexperia targeted 200 V/ns, matching the Common Mode Transient Immunity (CMTI) offered by modern gate drivers. CMTI measures the device’s ability to withstand fast common-mode voltage transients without unintended switching.
Nexperia’s testing shows that X.PAK SiC MOSFETs achieve 204.4 V/ns on the falling edge of drain-to-source voltage and sustained this for 50 hours (approximately 11 × 10⁹ cycles) without failure. For engineers deploying the technology, this level of dV/dt tolerance allows them to push switching speeds higher without risking device degradation, a key advantage in high-performance inverters and converters.
Moreover, X.PAK’s grooved package design ensures a 3.558 mm creepage distance, supporting high-voltage applications up to 1075V with pollution degree 1 for material groups I, II, and III. Engineers can also further enhance dielectric protection with insulating foils, gap fillers, or coatings.
Nexperia’s engineers have also optimized X.PAK’s pad arrangement to minimise parasitic inductances, reducing switching losses and improving high-frequency performance, while a dedicated Kelvin source pin separates the gate drive sensing point from the power source, improving gate voltage accuracy and reducing overshoot during fast switching.
The combination of these packaging features and top-side cooling allows X.PAK devices to take full advantage of SiC’s material benefits, empowering designers to attain higher power densities, improved efficiency, and reduced system costs more easily without sacrificing reliability.
Looking Beyond SiC: Holistic Design for Next-Generation Power Electronics
SiC brings undeniable advantages in switching speed, efficiency, and voltage handling, but material capability alone does not guarantee system performance. What ultimately matters is how the device is fabricated and assembled. Packaging, cooling, and integration turn SiC’s promise into measurable gains. Nexperia’s top-side cooled X.PAK devices illustrate this point: by refining thermal paths, minimising parasitics, and ensuring mechanical strength, they show that design discipline at the package level can unlock performance beyond traditional TO-263-7 devices.
For engineers, the challenge is to carry that same thinking into the system. Interface quality, mounting pressure, and overall assembly can define how much power a SiC device truly delivers in the field. A strong device still needs a strong thermal connection to its environment to sustain performance under real operating conditions.
While semiconductor material innovation creates the potential, packaging and integration turn it into performance. Recognising and optimising across these layers, from manufacturers such as Nexperia designing SiC semiconductors to engineers integrating the device, enables the creation of compact, efficient, and durable power systems that meet the growing demands of electric mobility and industrial automation.
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