No abstract

No abstract

This paper discusses different application relevant electrical loading cases of an IGBT module of a power inverter. Thereby, different operation conditions such as pulse frequencies, inverter output currents and output frequencies, as well as two different operation modes are discussed. Each load case investigation is conducted by electrical, thermal, and in situ vibration measurements. Moreover, on the base of finite element analyses a deeper insight is gained into reliability relevant thermo-mechanical behavior. For this purpose an IGBT module is operated at a load of 30% to 80% of its nominal value in order to cause representative thermomechanical displacements of dies and bond wires. By applying an inverter output frequency in a range of 1 to 280 Hz a temperature ripple of up to 40 K on the dies and a vertical displacement of up to 9 µm on a bond wire is observed. These results are important to improve life-timepredictions. IntroductionIGBT (Insulated Gate Bipolar Transistor) power modules are often used in electronic power inverters. Due to the high voltage and current level, any switching operation results in local power loss peaks in the die causing internal stresses. These stresses can be divided into electrical, mechanical, and thermal. Due to the thermal mismatch of adjacent materials temperature variations in system components cause stresses at their interfaces [1]. These stresses are related to material dependent strain and are known as the main factor of thermomechanical fatigue [2]. This may result in a relevant degradation of the devices and affect reliability. IGBT modules often operate at constant power levels for a long period of time, as e.g. in wind power stations [5,6]. During this period, at low inverter output frequencies, the components are exposed to a cyclic thermo-mechanical deformation due to the alternating current switching from the IGBT to the diode and back. The operation frequency for this process can range from 0 Hz to 300 Hz. Especially in traction application an electrical braking until full stop (0 Hz) is requested frequently. Due to the low frequencies (≤ 5 Hz) during a longer period of time the periodic temperature T ripple during the inverter output time period 1/f output increases. The pulse frequency f pulse is usually 1 to 5 kHz. The time to thermal steady-state of the module is approximately 1 s. Therefore, the temperature differences in the IGBT package increase and decrease according to inverter output frequency f output which is often labeled as operation frequency. This effect causes higher stresses in the package and could influence the life time.

No abstract

The subject of this investigation was determination of thenno-mechanically induced displacement of the components inside a power module under operation conditions. It is well known that lifetime of insulated gate bipolar transistor (TGBT) modules is limited by thermo mechanical fatigue. Wire bonded interconnects inside the TGBTs count as critical sites where crack initiation and failure is observed. In this study the temperature dependent periodic deformation of wire-bonds under operating conditions was determined by using a laser Doppler vibrometer (LDV) and thermal imaging camera. Furthermore fmite element analyses (FEA) were conducted to obtain the strain values needed for lifetime assessments.