In the era of energy transition and rapid development in automotive electronics, wide bandgap semiconductor materials such as silicon carbide (SiC) and gallium nitride (GaN) have been widely adopted in automotive modules and high-power systems. This has driven new challenges in device performance, dissipation, and reliability, with increasingly stringent validation standards on the road.
DEKRA iST was invited to participate in the “Seminar on Thermal Resistance and Lifetime of Power Devices” hosted by OITC on June 20 at the Sheraton Hsinchu Hotel. Bobby Hsieh, Technical Manager of Component Engineering Department, delivered a presentation titled “Introduction of Power Device Thermal Resistance & Power Cycling Test” He provided in-depth insights into thermal resistance testing methods, power cycling test techniques, practical validation experience, and the latest development of international standards, helping the industry grasp the critical elements of reliability validation.
Standard Updates and Trends of Power Devices
At the seminar, Bobby Hsieh shared AEC's latest updates on standards for wide bandgap (WBG) semiconductor devices. In light of the overview, the industry is able to stay informed on the evolving trends in testing standards.
- High Humidity, High Temperature and High Voltage Reverse Bias Test (H3TRB): The old standard required applying 100V at 85°C/ 85% RH. The updated version, revised to reflect the characteristics of wide bandgap (WBG) semiconductor devices, removes the 100V cap. It now allows the application of high voltage up to 80% of the device's rated voltage, which is better aligned with real-world stress conditions.
- Highly Accelerated Temperature and Humidity Stress Test (HAST): A HAST requires 96 hours of electrical biasing while maintaining 130°C and 85% RH, equivalent to 1000 hours of H3TRB testing. Although the updated AEC guideline no longer recommends HAST as a formal validation method (to avoid issues like arching), it is still commonly used in practice as a supplementary tool for rapid screening, particularly suitable for early-stage assessment during R&D.
- Temperature Cycling Test (TCT): As one of the typically used methods for lifetime estimation, TCT is employed to verify the overall reliability after package design and process integration. It entails vertical integration between upstream and downstream processes, using final packaging (e.g., TO-247) for testing to screen for potential structural failure caused by thermal expansion stress.
- Intermittent Operating Life (IOL): It is a dynamic reliability test that simulates repeated on/off switching cycles and thermal cycling. The test is designed to run the device at 25°C ambient environment that activates self-heating to raise the junction temperature to 125°C–150°C. This method, a closer approximation to real-world applications, helps verify whether the device can maintain long-term stability under harsh operating conditions.
Power Device Validation and Testing Analysis
AQG analysis highlights that boosting current withstands capability alongside optimized thermal resistance design plays a key role in extending device longevity. Data shows that a 10% drop in thermal resistance can potentially increase device lifespan by up to 40% under identical conditions. On the flip side, inadequate thermal design can lead to local overheat, increasing the risk of reliability concerns.
To measure thermal performance, DEKRA iST adopts the T3STER thermal transient tester to analyze the structure function according to the JESD51 series standards. The system can support up to 240A. The process involves selecting appropriate heating and sensing methods, setting current parameters, and using the T3STER to record real-time power, voltage, and temperature profiles. This data is then used to calculate thermal resistance (Rth) and junction temperature difference (ΔTj). By understanding the distribution of thermal resistance across each structural layer, engineers can fine-tune packaging design and ensure that high-power electronic devices achieve greater performance and reliability in future applications.
Bobby also dissected a practical case study during the seminar. He illustrated how the Safe Operating Area (SOA) is derived from actual device data. By calculating changes in thermal resistance under different duty cycles, it becomes possible to define the cap for instantaneous current and breakdown voltage effectively. Power Cycling Test is divided into two scenarios:
- PC sec Cycling: Short-duration switching (less than 5 seconds), where thermal stress is primarily concentrated around structures near the chip, such as a solder layer.
- PC min Cycling: Long-duration switching (greater than 15 seconds), allowing heat to transfer from the chip to the outer package. This produces mechanical stress across the entire module, affecting processes like wire bonding and system-level welding.
Finally, Bobby elaborated on the implementation of the Power Cycling Test using the Power Tester 2400 solution for testing, monitoring, and analysis. During testing, operational parameters such as maximum junction temperature (Tj-max), thermal resistance (Rth), and turn-on voltage (Von) can be monitored in real time to obtain instant insight into data. In addition, infrared thermography can be incorporated to quickly identify local heat generated on a sample. With parallel circuit modules, the testing capability is scaled up to 2400A in order to accommodate various stress conditions and test setups across different types of samples.
Conclusion
As the technology of wide bandgap (WBG) semiconductor continues to advance, reliability validation and testing standards are evolving toward more rigorous and practical approaches. DEKRA iST remains committed to staying at the forefront of standard updates, while continuously strengthening its expertise in power device testing, thermal management, and reliability validation. By identifying potential thermal risks early in the product design phase, DEKRA iST aims to support customers in enhancing both performance and lifetime of their devices.
Looking ahead, DEKRA iST will continue to deliver comprehensive reliability validation solutions spanning from device to system level. We work closely with customers to tackle the multifaceted challenges that power devices face under thermal, electrical, and environmental stresses, paving the way for next-generation electronic applications that are of high efficiency and high reliability.
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