Structure functions measured with Simcenter POWERTESTER hardware can be used to improve the accuracy of the thermal simulation models of power modules. The results are imported directly into Simcenter Flotherm, Simcenter Flotherm XT and Simcenter FLOEFD. These Simcenter software solutions are available with an optional module that automatically optimizes the values of user-nominated model inputs to match the structure function for the model to that of the measured part. The result is a thermal model of the package that is accurate to better than 99% for all time constants, supporting high-fidelity thermal simulation for any use case or power profile.

Simcenter POWERTESTERs give you the greatest confidence in the power electronics you create, support the use of validated thermal models, and underpin the fidelity of your thermal design.

Hundreds of Simcenter POWERTESTER solutions have been sold for use worldwide across a wide range of industries. Alarms, status indicators, and safety features equip these systems for deployment in environments, ranging from research laboratories to industrial test facilities. Systems incorporate an autonomous safety monitoring unit operated from a built-in uninterruptable power supply (UPS). A 4 color tower light with buzzer indicates the status of the system, which has a manual stop button. Power cycling systems require 3-phase power and liquid cooling or process water as services.

The Electrical Test Method is a non-destructive approach, standardized by JEDEC (JESD51-1), which uses the temperature-dependent properties of a semiconductor device, such as the forward voltage for a diode, to determine its temperature during thermal testing. The die can be both powered and sensed simultaneously throughout the test, to measure temperature vs. time during thermal characterization.

Fidelity of the measurement of the electrical signal is equivalent to a resolution of ±0.01°C. A key advantage of this approach is the opportunity to use the zero-time temperature of the semiconductor device as the reference temperature rather than using a separate thermocouple.

Simcenter POWERTESTER hardware systems are capable of power cycling the parts under test under a variety of conditions to match the different operating conditions the parts will experience in the field. These systems offer comprehensive cycling strategies and capture a range of electrical and thermal test data, in addition to regular thermal transient measurements during the testing.

The simplest of these is to use pre-defined power-on and power-off periods at fixed current, without compensation for temperature rise or power. Damage the part experiences as it is fatigued will cause the case temperature, junction temperature, and power dissipation to increase over the course of the test, which can take many tens of thousands of cycles. Alternatively, the test can be run with any of these parameters held constant to a high level of accuracy, by varying the supplied current or gate voltage during each cycle.

Transient thermal impedance measurements are performed periodically during power cycling, and the resulting temperature vs. time graph is post-processed into a thermal structure function. A structure function plot shows the cumulative thermal capacitance versus thermal resistance of the device when the heat is transferred from the die junction to the ambient.

Structure functions provide insight into the thermal performance of constituent part of the package structure, such as the solder die attach layer beneath the die, with part-to-part differences arising from manufacturing variability in thickness, contact resistances, and the presence of voids. Structure function analysis provides a non-destructive approach to assess changes in the package thermal structure during power cycling, as shown in the image.