Presentation Description: Long term reliability of silicon carbide (SiC) and gallium nitride (GaN) devices, modules, and systems is an important topic as they are being deployed in mission critical applications such as EV’s, aircraft, industrial electrification, as well as renewable energy systems and grid enhancements and updates. Power electronics systems must operate under many different operating and environmental conditions, which is driving the need for high reliability over a lifespan that could easily be 10-15 years. Failures and the failure modes must be detected quickly, even in the design cycle, to ensure reliability.
Time Domain Reflectometry (TDR) is a technique that measures reflections along a conductor. TDR can be used to locate faults in cables, electrical lines, printed circuit board (PCB) discontinuities, or any other electrical path by observing reflected pulses. The TDR measures the time a pulse takes to issue from and to the source, and using that data, can compute a number of characteristics of the transmission medium. This enables the design and engineer to quickly locate conductor breaks or changes and understand possible failure modes.
Based on TDR impedance measurements, the design engineer can perform signal and power integrity analysis on power semiconductor devices, modules and systems, printed circuit boards, power interconnects, and connectors, with the intent to locate faults more accurately and quickly. For example, TDR can be used to detect wire bonding breaks in power modules, which is important to ensure long term reliability of the module. The TDR analysis automatically calculates the reflection coefficient (rho) versus time waveform from the reflected signal and plots an impedance (Z) versus time trace. A measurement badge displays the impedance (Z), capacitance (C), and inductance (L) by automatically identifying the region of interest where the impedance has changed.
Today, modern real-time oscilloscopes, coupled with add-on analysis tools, are commonly used as the tool of choice for making TDR measurements due to their portability, ease of use, lower cost (compared to traditional TDR instruments), and increased scope bandwidth and sampling rates. Engineers can perform TDR measurements with a simple setup including mixed signal oscilloscopes, a TDR module, and either SMA cables or TDR probe.
As a measurement instrument company, we believe this presentation is important to share with engineers so they can be equipped with the right tools and measurement techniques to ensure reliability of the devices and systems they are designing and producing. TDR is one such technique.
