High Power IGBT Modules Research Articles

Instable mechanisms during unclamped operation of high power IGBT modules

The behaviour in terms of robustness during unclamped operations of power IGBT modules is presented. The experimental characterization is aimed to identify the main instable phenomena during unclamped turn-off in power IGBT modules. Several devices of different generations, current and voltage ratings have been analyzed. Thanks to a non-destructive experimental set-up, it is possible to observe instable phenomena without causing the damage of the device under test. In this paper, it is shown that the destructive conditions during unclamped operations are preceded by precursors on the gate side which indicate instable phenomena taking place inside the device. The dependence of the destructive phenomenon on the driver conditions are widely and exhaustively analyzed.

IGBT modules robustness during turn-off commutation

The behaviour in terms of robustness during turn-off of power IGBT modules is presented. The experimental characterisation is aimed to identify the main limits during turn-off in power IGBT modules in typical hard switching applications. In this paper an experimental characterization of high power IGBT modules at output currents beyond RBSOA, at high junction temperatures and under different driving conditions is presented. Several devices of different generations, current and voltage ratings have been considered. The experimental characterisation has been performed by means of a non-destructive experimental set-up where IGBT modules are switched in presence of a protection circuit that is able to prevent device failure at the occurrence of any possible instable behaviour. The experimental analysis confirms the very good robustness of high power IGBT modules which can withstand large current overstress well beyond the declared RBSOA limits even at temperatures larger than those one declared by manufacturers. A comparison between IGBT device generation is also presented.

Lifetime analysis of solder joints in high power IGBT modules for increasing the reliability for operation at 150 °C

The increased demand for higher operating junction temperatures in IGBT modules is a main challenge for future packaging technologies. Two critical design features regarding this aspect include the terminal solder joints and the large area solder joints. The main focus of this investigation is on the consequences of raising the maximum operating temperature of IGBT modules and the required design modifications of solder materials at a microstructure level for tackling the drawbacks of state-of-the-art technologies.

Degradation behavior of 600 V–200 A IGBT modules under power cycling and high temperature environment conditions

One challenge for automotive hybrid traction application is the use of high power IGBT modules that can withstand high ambient temperatures, from 90 °C to 120 °C, for reliability purpose. The paper presents ageing tests of 600 V–200 A IGBT modules subjected to power cycling with 60 °C junction temperature swings at 90 °C ambient temperature. Failure modes are described and obtained results on the module characteristics are detailed. Especially, physical degradations are described not only at the package level, like solder attach delaminations, but also at the chip level, with a shift on electrical characteristics such as threshold voltage. Finally, numerical investigations are performed in order to assess the thermal and thermo-mechanical constraints on silicon dies during power cycling and also to estimate the effect of ambient temperature on the mechanical stresses.

The robustness of series-connected high power IGBT modules

The behaviour in terms of robustness of series-connected high power IGBT modules is presented, arranged in a topology which ensures voltage balance on IGBT’s and diodes by means of a simple auxiliary circuit applied directly on the high power devices, which are used in hard switching mode. Analyses in terms of IGBT and diode SOA (safe operating area), collector to emitter voltage gradient and short circuit condition are reported as well as an extended experimental characterisation. Both analyses confirm superior switching rating and system reliability, by using two series-connected IGBT in substitution of a single module, same current and double voltage rated. Moreover, thanks the auxiliary circuit presence, the robustness of total system is maintained also in extreme operating conditions.

The high frequency behaviour of high voltage and current IGBT modules

Sharp voltage gradients act as a stimulus for high power IGBT modules, which can exhibit a potentially instable high frequency behaviour. In fact, they can act as a radio frequency amplifier and, in particular operating conditions, the interaction between the device and the control or the external circuit can cause self-sustaining oscillations or the enhancement of the unevenness in current distribution inside a power module thus having a significant impact on the reliability of the power converter. Moreover, this RF amplification worsen the generated EMI (Electro Magnetic Interference). This paper presents an extensive experimental investigation about the high frequency behaviour of IGBT high power modules. The measurements were performed by means of an original experimental set-up that was specifically conceived and constructed. The data are analysed with the help of a theoretical small signal model which is able to describe RF behaviour of high power IGBT modules.

Boundary element analysis of thermal fatigue effects on high power IGBT modules

The technology of high power IGBT modules has been significantly improved these last years against thermal fatigue. The most frequently observed failure modes, due to thermal fatigue, are the solder cracks between the copper base plate and the direct copper bonding (DCB) substrate and bond wire lift-off. Specific simulation tools are needed to carry out reliability researches and to develop device lifetime models. In other respects, accurate temperature and flux distributions are essential when computing thermo-mechanical stresses in order to assess the lifetime of high power modules in real operating conditions. This study presents an analysis method based on the boundary element method (BEM) to investigate thermal behavior of high power semiconductor packages subjected to power cycling loads. The paper describes the boundary integral equation which has been solved using the BEM and applied to the case of a high power IGBT module package (3.3 kV–1.2 kA). A validation of the numerical tool is presented by comparison with experimental measurements. Finally, the paper points out the effect on the thermal stress of the IGBT chips position on the DCB substrate. In particular, a light shifting of the silicon chips may be sufficient to delay significantly the initiation and the propagation of the cracks, allowing a higher device lifetime of the studied module.

High field, high repetition rate kicker

New kicker magnet systems and their related technologies are being developed and tested at KEK. The kickers are to be used both for the injection and for the fast extraction of two rings, the 50GeV proton synchrotron in the ‘Joint Project’ of JAERI–KEK and the PRISM/FFAG ring for the muon beam. In order to obtain a sufficient kick on the high-intensity beam in the 50GeV proton ring, the kicker systems must have both large apertures and high fields. In addition to this, the PRISM/FFAG ring demands muon beams with a high repetition rate of injection and extraction. The requested repetition rate is 1kHz or higher.In order to fulfill those demands, new technologies have been introduced and are now being tested. Among them are high-power IGBT modules, a subordinated-gating system, 1kHz repetition pulsed power supply, and kickers with magnetic-alloy cores used as return yokes.

Reliability Enhancement of Solder Joints Made by a Void Free Soldering Process

This paper examines microstructures and the reliability of solder joints made by a new void-free process and compares them to the conventional H2 process. A new two step void-free process was recently developed for enhancing the reliability of large area, high power IGBT modules. First, Ar+ were used to clean the surface of plated Ni films on a substrates followed by coating with 0.5 \\micron Ag film, and second, 50 mass% Pb–Sn solder sandwiched between the two substrates was heated at 503 K in vacuum for 5 min. and then cooled in a N2 atmosphere. The fatigue life time of the solder joints formed by the new process was found to be 3 times longer than those made the conventional process. We also found the solder joints from the new process to have considerably smaller amounts of micro and interfacial voids in comparison by those made with the conventional method.

Reliability testing of high-power multi-chip IGBT modules

Power-cycling tests are among the most important tools used for evaluating the reliability of power modules. They are in most cases carried out at the rated module current and during a relatively short cycle time, i.e. under worst-case operating conditions. Test conditions must be defined which also permit information to be obtained about failure mechanisms in the various parts of the module. This paper describes the measurement of the temperature distribution, the test conditions, the rates of temperature change in modules with 36 semiconductor components as well as the results of power-cycling tests in which the thermomechanical stress principally affects the substrate-baseplate interface.

Reliability and lifetime evaluation of different wire bonding technologies for high power IGBT modules

Abstract IGBT modules for power transmission, industrial and traction applications are operated under severe working conditions and in harsh environments. Therefore, a consequent design, focused on quality, performance and reliability is essential in order to satisfy the high customer requirements. One of the main failure mechanisms encountered in high power IGBT modules subjected to thermal cycles is wire bond lift-off, which is due to the large thermal expansion coefficient mismatch between the aluminum wires and the silicon chips. The paper describes various bonding technologies using different wire materials directly bonded onto chip metallisation as well as the ABB solution where the wire is bonded on a thin molybdenum strain buffer soldered onto the chip. We assess in the present paper the potential of these technologies to enhance module reliability and lifetime through a power cycling test. Failure analysis results are presented and the failure mechanisms related to each technology are explained in detail.

Some observation dealing with the failures of IGBT transistors in high power converters

The explosion strength of high power IGBT modules is one of the important parameters that may decide on converter equipment reliability in extreme circumstances. The explosion strength of a device is represented by the peak value of the collector current (so called “peak case nonrupture current”) that cannot be exceeded. Some main IGBT failure mechanisms under service conditions are discussed. Test methods and experimental results on device case explosion strength are presented. Experiences concerning starting, tests and service of high IGBT converters are given. Preliminary load tests with rapidly changing current values are useful for newly fabricated IGBT converters.

Substrate-to-base solder joint reliability in high power IGBT modules

Acoustic microscope imaging proved to be an excellent tool to detect and quantify solder fatigue of the substrate to base interface of high power IGBT modules. This technique was used to establish the dependence of the thermal cycling capability on the temperature swing of the module base for a A1N Cu system. Results from temperature cycling tests were combined with results from power cycling tests to predict the solder joint reliability over a wide range of temperature excursions.

Effects of current density and chip temperature distribution on lifetime of high power IGBT modules in traction working conditions

This paper deals with ageing parameters of high power IGBT modules in traction applications. Using the results of a great number of power cycling tests on 400A modules, it shows that, in addition to the junction temperature excursion, other parameters like the maximal chip temperature and the current density are involved in thermal fatigue failures. Besides, contact temperature measurements achieved on IGBT chip surface in cycling conditions to localise the maximal thermomechanical stress are presented and correlated with modules failure analysis. The role of the current density in the ageing process is finally shown by determining its influence on the temperature gradient on chip surface.