Advancements in Packaging Technologies for SiC Power Semiconductor Cooling
Packaging is playing an increasingly important role in power semiconductor performance, particularly when looking at wide-bandgap materials that deliver higher power in a smaller footprint.
Recent years have witnessed a paradigm shift in power electronics driven by the integration of wide bandgap (WBG) semiconductors, particularly silicon carbide (SiC). SiC semiconductors boast superior material properties, translating to a demonstrably lower knee voltage at an equivalent breakdown voltage compared with their silicon (Si) counterparts.
This inherent advantage has led to smaller device footprints, lower stored charge, and reduction in switching losses. These relative improvements over silicon deliver the potential for significantly higher operating frequencies within SiC-based devices designed for similar voltage and current ratings.
Compact Thermal Management Packaging Technologies for Power Semiconductors
Silicon devices typically have a maximum junction temperature of around 150 °C, while SiC semiconductors can safely operate well above 200 °C, reaching upwards of 300 °C depending on the specific device and application. However, as with any semiconductor, the thermal path from a junction to the environment in a packaged SiC device plays a critical role in its performance and reliability.
The semiconductor device package includes many components, such as die-attach, interconnects (such as wire bonds), metal-ceramic substrates, baseplates or lead frames, encapsulants, and terminals. The thermal conductivity (k) of these materials and the thermal resistance (Rth) of these layers and interfaces might impact the ability to dissipate heat away from crucial regions of the semiconductor.
Advances in Power Packaging and thermal management: A snippet from Thomas Hauer's interview with electropages
Packaging design will minimize Rth_JA and maintain TJ below the maximum specified temperature (TJ_max) for the SiC semiconductor device. Optimizing package geometry (minimizing bond wire length and maximizing surface area for heat dissipation) can improve thermal performance.
Major semiconductor manufacturers like STMicroelectronics (ST), onsemi, and Navitas Semiconductor, have developed novel packaging technologies addressing the thermal challenges of SiC, which allows for higher operating temperatures compared to silicon.
The key benefits of these advanced packaging technologies lie in their enhanced thermal regulation, ability to handle higher power densities, and compact designs, leading to improved performance and cost efficiency in high-power electronics.
Advanced SiC Packaging Technologies from Major Semiconductor Manufacturers
STMicroelectronics, a pioneer in the research and development of SiC power semiconductors aimed at the automotive industry, has productized three innovative packaging technologies for SiC that provide unique benefits and features: STPAK, HU3PAK, and ACEPAK SMIT.
HU3PAK Top-Side Cooling Saves Space
The main feature of this packaging technology is its efficient top-side cooling. This is beneficial for applications where space constraints limit heatsink size or where airflow is primarily directed from the top.
When correctly mounted, the package’s typical thermal resistance from junction to case (RJC) is 0.51 °C/W, and from junction to ambient (RJA) is 30 °C/W. This represents a reduction in (RJA) of up to 18 % compared to the more common bottom-side cooling approach used in D2PAK and TO-LL.
Figure 1 shows the top side, featuring a wide thermally conductive pad, of an ST SiC MOSFET offered in the HU3PAK package.
HU3PAK's top-side cooling allows for smaller heatsinks. This enables more compact semiconductor device designs. The advanced surface-mounted HU3PAK package allows a smaller form factor, higher design flexibility, and better thermal performance while increasing the power density.
Figure 1: An STMicroelectronics SiC MOSFET in HU3PAK package (Source: STMicroelectronics)
Figure 2: Heatsink mounted on the top side of an ACEPAK SMIT SiC power semiconductor (Source: STMicroelectronics)
ACEPAK SMIT Insulated Top Side Reduces Electrical Leakage
Similarly to the HU3PAK, the ACEPACK SMIT package is designed to be surface mounted on a printed circuit board, while having its opposite top side connected to an external heatsink. However, the major characteristic of the ACEPAK SMIT package is its insulated top side. This surface provides electrical isolation between the packaged component and the heatsink, improving safety and overall system reliability.
An example of the application of a large heatsink is shown in Figure 2. The SiC MOSFET is soldered on the PCB on one side, while its top side is in contact with the heatsink.
Navitas SiCPAK Press-Fit Technology and Silver Sintering Improve Cooling and Reliability
Navitas Semiconductor has improved upon the industry-standard SiCPAK package technology in its silicon carbide power portfolio. The SiCPAK modules use a press-fit technology that is built upon the same modules used by the company’s GeneSiC that have already been proven for their superior performance, reliability, and rugged durability.
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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.
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The "press-fit" technique offers cost-effective, high-power solutions and compact designs for power circuits, catering to end customers' needs. SiCPAK does not contain any lead. Instead of using soldering, each SiC chip is joined to the module's substrate by a process called silver (Ag) sintering. This method not only ensures improved cooling but also enhances the reliability of the module. The substrate is fabricated by employing an active-metal brazing (AMB) process on silicon-nitride (Si3N4) ceramics, resulting in direct-bonded copper (DBC). This approach is optimal for power-cycling applications. Advanced construction processes provide exceptional strength and flexibility, resistance to fractures, and high heat conductivity, ensuring reliable and long-lasting performance.
onsemi EliteSiC Direct Cooling Eliminates Need for Thermal Interface Layer or Heatsink
onsemi provides innovative direct cooling methods as part of its packaging alternatives. These technologies enhance thermal conductivity, resulting in improved system performance and reliability. Integrating full SiC MOSFETs, onsemi’s EliteSiC power modules provide a direct cooling path between the coolant and the SiC chip without requiring additional thermal components like TIM or heatsinks.
SiC Packaging Technologies Increase Performance and Reliability in EV Power Systems
Traditional silicon (Si) electronics are disadvantaged in high-power applications like electric vehicle (EV) drivetrains, onboard chargers (OBCs), and EV DC fast charging stations due to limitations in switching speed and heat dissipation.
Figure 3: onsemi’s Direct and B2 SiC package options (Source: onsemi)
Silicon Carbide (SiC) offers a superior alternative, but its packaging requires a careful design. The innovative SiC packaging mentioned is changing the game for Original Equipment Manufacturers (OEMs) designing EV power systems.
These innovative SiC packaging technologies offer a range of benefits, including:
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Higher performance: Improved thermal management and reduced electrical resistance translate to higher power densities and switching frequencies. This allows for smaller, lighter, and more efficient power electronics for the EV drivetrain.
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Increased reliability: Improved thermal performance and lower switching losses contribute to increased reliability and longer lifespan of the power electronics.
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Faster charging times: Higher power densities enable more power in the same area.
In summary, advancements in SiC packaging technology are transforming power electronics through improved thermal management. Innovations from manufacturers like STMicroelectronics, Navitas Semiconductor, and onsemi enable SiC semiconductors to achieve durability, energy efficiency and reliability, driving progress in high-power industries such as automotive.
For more information about SiC power semiconductors, talk to the Avnet Silica Power Specialists.
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