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.     

Thermal characterisation of power modules

This paper describes the thermal characterisation of power modules by means of a variable spreading angle model extended to multilayer structures. The model is used for thermal resistance calculation of assembled chips as a function of their size and according to the module construction and structure. This way of presenting thermal data is very useful to module manufacturers and users, allowing them to carry out an easy estimation of the thermal performance before building or ordering the module, so they can conform better to the application. Moreover, due to the closed form nature of the model, it can also be used for a quick estimation of the influence of the different parts and materials that constitute the module, in order to optimise its final structure. Experimental measurements carried on modules assembled with die of known sizes show good correlation with the calculations.     

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.     

Thermal impedance spectroscopy of power modules

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.     

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.     

Double-sided cooling for high power IGBT modules using flip chiptechnology

A new technique for the packaging of IGBT modules has been developed. The components are sandwiched between two direct bond copper (DBC) substrates with aluminum nitride. Wire bonds are replaced with flip chip solder bumps, which allows cooling of components on both sides. Microchannel heat sinks are directly integrated in the package to decrease the thermal resistance of the module. Thus, a very compact module with high thermal performance is obtained. A prototype with two insulated gate bipolar transistors (IGBTs) and four diodes associated in parallel was realized and tested. In this paper, the innovative packaging technique is described, and results of thermal tests are presented     

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.     

Thermal characterization of power transistors

The idealized concept of thermal resistance as applied to power transistors is discussed. This concept must be used with care because two of the basic assumptions made in applying the concept to these devices are not valid. Contrary to these assumptions, it is shown that 1) the junction temperature of a power transistor is never spatially uniform, and 2) no unique value of thermal resistance can be defined for all operating conditions. Also, various electrical methods for measuring the junction temperature (thermal resistance) of power transistors are discussed with the emphasis placed on the emitter-only switching measurement technique, which is the preferred standard method of measurement. In addition, the generation and meaning of forward-biased safe-operating-area (SOA) limits are discussed, and it is shown that because of the presence of current crowding and the associated hotspots, the specified SOA limits often permit devices to be operated at dangerously high junction temperatures. Electrical measurement methods capable of determining the peak junction temperature as well as determining the onset of current crowding are described, and it is shown how these methods might be used for the generation of improved SOA limits.     

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.     

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.     

Monitoring of paralleled IGBT/diode modules

A method is presented to monitor the state of a converter with an unlimited number of paralleled insulated gate bipolar transistor (IGBT)/diode modules with individual gate drives. The monitoring functions can be implemented without extra signal processing or load-side components. The method is based on the active gate-controlled current balancing (CB) principle. This principle is reviewed in the first part of this paper, and the necessary supplements to implement the monitoring functions are shown. In the second part, experimental measurements are shown. This new control method allows monitoring the state of a converter and balancing the losses and current sharing between paralleled power devices, without the need to match the devices nor the gate drives. Thus, the overall reliability can be increased without increasing the costs. Since no matching of the devices is needed, the handling and logistic costs can be significantly reduced. IGBT/diode modules for standard paralleling are selected, and only modules of the same class can be paralleled without excessive derating. The presented method allows switching off one of the paralleled branches in the case of parameter degradation and to keep the converter operating at a lower power     

Ageing defect detection on IGBT power modules by artificial training methods based on pattern recognition

The ageing of power insulated gate bipolar transistor (IGBT) modules is mainly related to thermal and thermomechanical constraints applied to the device. This ageing causes degradation of the device performances and defects appearance which can lead to failures. To avoid these failures, the follow-up of the device operation and the detection of an ageing state remain a priority. This paper presents, at first, ageing tests of 1200 V-30 A IGBT module subjected to power cycling with the aim to highlight online and real-time measurable external indicators of ageing. Secondly, these indicators are used to develop a failure diagnosis method. The diagnosis is realized by artificial training methods based on pattern recognition.     

Thermal fatigue effects on the temperature distribution inside IGBT modules for zone engine aeronautical applications

This work examines the thermal fatigue effects on the temperature distribution inside IGBT modules for aeronautical applications. Exactly, they are used in a very different application where temperature cycling due to the working environment is the most limiting fact. In this case, it is concluded that solder delamination does not present any restriction to module lifetime at short term (up to 60% of total delaminated area). In addition, it is proposed only determining the delaminated area behind devices, which is the main responsible of the thermal temperature increase.     

Thermal management of power electronics modules packaged by a stacked-plate technique

The research presented in this paper is part of a multidisciplinary research program of the Center for Power Electronics Systems at Virginia Tech. The program supported by the Office of Naval Research focuses on the development of innovative technologies for packaging power electronics building blocks. The primary objective of this research is to improve package performance and reliability through thermal management, i.e., reducing device temperatures for a given power level. The task of thermal management involves considering trade-offs in the electrical design, package layout and geometry, materials selection and processing, manufacturing feasibility, and production cost. Based on the electrical design of a simple building block, samples of packaged modules, rated at 600 V and 3.3 kW, were fabricated using a stacked-plate technique, termed metal posts interconnected parallel plate structure (MPIPPS). The MPIPPS technique allows the power devices to be interconnected between two direct-bond copper substrates via the use of metal posts. Thermal modeling results on the MPIPPS packaged modules indicate that the new packaging technique offers a superior thermal management means for packaging power electronics modules.     

Strategy for designing accelerated aging tests to evaluate IGBT power modules lifetime in real operation mode

Accelerated aging tests are widely used in electronics industry to validate the technological choices of packaging, especially when significant lifetime is required. The thermal coefficient of expansion mismatch between the soldered materials results in crack propagation in the solder joints, which irreversibly increases the thermal resistance of the assembly and progressively leads to the failure of the module. Accelerated testing is very expensive and can last a long time, so that such experiments must be optimized. In addition, thermomechanical behavior of the assembly under realistic operating conditions for long times can be studied in shorter times thanks to finite element simulations. Non-linear finite element simulations have been carried out to make a correlation between accelerated aging tests and real operation. Stress-strain history under representative thermal loading has been determined in both cases. The energy dissipated in solder joints has been calculated and has been used as an estimator of the damage in the solder joint. Finally, thermal fatigue experiments with representative samples have allowed validating the previous results. This study is a step toward the understanding of the correlation between accelerated testing and actual operating conditions.     

Temperature measurements and thermal modeling of high power IGBT multichip modules for reliability investigations in traction applications

To study the failure mechanisms induced on high power IGBT multichip modules by thermal cycling stress in traction environment, a good knowledge of the temperature distribution and variations on the chips and in the interfaces between the different layers of the packaging is necessary. This paper presents a methodology for contact temperature measurements on chips surface in power cycling conditions and a fast 3D thermal simulation tool for multilayered hybrid or monolithic circuits. The results of static and dynamic thermal simulation of a 1200A–3300V IGBT module are given and compared with the contact temperature measurements results. The investigation has been done within the RAPSDRA (Reliability of Advanced High Power Semiconductor Device for Traction Applications) European project.     

高压IGBT模块局部放电研究现状

IGBT(Insulated Gate Bipolar Transistor)模块一直朝着更高耐压和更大电流密度的方向发展,因模块内部电气绝缘和局部放电引起的问题也越来越明显。在高电压IGBT模块封装中,通常使用硅凝胶和环氧树脂来对模块进行灌注和密封,以满足其高电场承受能力,提升整个模块的绝缘性能和局部放电表现。目前很多国内外学者已经在这方面进行一系列研究,主要目的在于优化IGBT模块内部的电场分布。本文重点介绍目前研究的几种可以改善IGBT内部电场分布状态的方法,并对局部放电可靠性的提升方法进行总结。     

大功率IGBT功耗的研究

绝缘栅双极晶体管(IGBT)是复合全控型电压驱动式功率半导体器件.为了改善其功耗性能并进行进一步优化,论文在阐述IGBT特性基础上,通过从器件构成和实际应用角度对影响功率器件功耗的主要因素进行分析,并结合实践对IGBT功率器件的功耗进行深入研究,由此可以更深刻地理解IGBT功耗的产生,这对正确选择和使用IGBT器件及其系统有一定的实用价值.     

Thermal stability of IGBT high-frequency operation

Thermal stability of high-frequency insulated gate bipolar transistor (IGBT) operation is studied in this paper. The nonpunch-through IGBT is found to be stable when operated within its rated temperature. Thermal runaway occurs with punch-through IGBTs at temperatures below the maximum junction temperature when operated at high frequency at well below rated current, with snubber or soft-switching circuits