M. Thoben

Thermo-mechanical analysis of bonding wires in IGBT modules under operating conditions

Abstract The lifetime of IGBT (Insulated Gate Bipolar Transistor) modules is limited by thermo-mechanical fatigue. Thereby bonding wires represent the critical links where damage initiation is observed. For the first time Laser Doppler Vibrometer measurements and thermal imaging were employed to determine the temperature-dependent deformations of bond wires at different frequencies under operation conditions. This should be considered as an important step to facilitate more precise life-time predictions of power modules in long term usage.

Power cycling testing and FE modelling focussed on Al wire bond fatigue in high power IGBT modules

Abstract Aging of Al wire bonds of IGBT modules is studied in power cycling tests and FEM simulations. For a clearer distinction of bond wire fatigue from solder delamination a die attach with high melting temperature is chosen to reduce the influence of chip solder aging. Test conditions cover a broad range of cycle amplitude Δ T j . The FEM model for bond wire fatigue achieves a good reproduction of the measured dependence of cycle numbers on Δ T j . A low impact of absolute temperature on N cyc is confirmed both by experiment and theory.

Thermal impedance spectroscopy of power modules

Abstract In this paper, a method of thermal impedance spectroscopy for power modules is presented. This method enables a high resolution non-destructive analysis of the power module by means of electrical measurement and subsequent mathematical evaluation. The result provides a separation of partial thermal resistances corresponding material layers and facilitates a plausible estimation of geometrical dimensions of the power module package within the heat flow path. This method is applied for localization of failures during power cycling test.

Lifetime modeling and simulation of power modules for hybrid electrical/electrical vehicles

Abstract In hybrid electrical vehicles (HEV) and electric vehicles (EV) power semiconductors, packaged in a module, are used. Packaging technologies are suffering several wear out mechanisms, that are typically induced by thermal or power cycling. The type of wear out mechanism is affected by the connection technology but also by the load type. In the design of the inverter the mission profile simulation of the power module is an important step to ensure operation of the power module over the complete vehicle lifetime. Influences of application parameters are presented. Physics of failure based FEM simulation can help to develop appropriate lifetime models which are basis for the mission profile simulation. Available power module technology achieves the lifetime requirement for hybrid electric vehicles/electric vehicles, if the described method is applied in the design phase of the inverter.

Experimental and analytical study of geometry effects on the fatigue life of Al bond wire interconnects

The reliability of power electronic devices is mainly limited due to thermo-mechanical fatigue of the internal bond wire interconnections. The bond wire shape is already defined at the design stage of the device. Thus preliminary lifetime assessments become more and more important in order to satisfy the high quality demands and the short time to market of the devices. In this study a fast experimental test setup is used in order to determine the lifetime of a large number of wire bond shapes. Furthermore an analytical model is applied to calculate optimized wire bond shapes for a given set of parameters. The results of this investigation should help to optimize the shape parameters at an early stage of development using the presented analytical model in combination with the fatigue tests.

Thermal impedance spectroscopy of power modules during power cycling

The presented thermal impedance spectroscopy of power modules simplifies significantly the failure analysis of power modules. It enables online observation of degradation within the cooling path with detailed information about failure mechanisms. The degradation of certain layer within the power module is detected by observation of Zth parameters. Several tests results are compared with analysis of the scanning acoustic microscope.

Power cycling tests at high temperatures with IGBT power modules for hybrid electrical vehicle applications

In this publication, test results of power cycling tests are presented with 600V IGBT power modules for hybrid electrical vehicle (HEV) applications at high junction temperatures. First, the power cycling capability of standard packaging technology in wide ΔTj range is investigated. Afterwards the reliability improvement of new packaging technologies is shown.

Electro-thermal analysis of in situ vibration measurements on IGBT modules under operation conditions

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 thermo-mechanical 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-time-predictions.

Experimental investigation of transient electrical, thermal and mechanical behavior of IGBT inverter modules during operation

This study comprises the electrical analysis of an experimental investigation on thermo-mechanical vibration measurements on an IGBT inverter structure under operating conditions and shows a new way how to experience reliability relevant phenomena. In order to perform transient temperature measurements with IR thermography and optical vibration measurements one sub-system of the inverter module was extracted and operated at equivalent conditions. Necessary circuit modifications including parasitic impedances and their most important influences are discussed. The investigation revealed a strong dependence of the thermo-mechanical bonding wire vibrations on the inverter output frequency. At 1 Hz an amplitude of more than 4 μm was measured at the loop peak of a short bonding wire.