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.     

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.     

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.     

Active Voltage control of IGBTs for high power applications

The operation of an insulated gate bipolar transistor (IGBT) in its active region is a well established technique for withstanding short circuits and also for dv/dt control. In this paper, we exploit the active behavior of the IGBT, applying a voltage feedback loop to the IGBT to control its switching. It is shown that adding a bias to the demand reference waveform shifts the IGBT into the active region and permits wide bandwidth operation over most of the switching transient. The operation of the IGBT is reported in detail, making reference to a selection of experimental waveforms for 400-A, 1700-V capsule IGBTs. The implementation required for control of such large IGBT modules and capsule devices for high power applications is described and discussed. It is concluded that the active voltage control method allows the operation of high power IGBT circuits to be closely defined.     

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.     

Statistical analysis of characteristic of ageing precursor of IGBT based on synthetic effect of multi-physical fields

The IGBT power modules are widely used in photovoltaic power generation, high-voltage direct current transmission and other fields. Due to the need for high reliability in the application fields, the industry is very concerned about the reliability of IGBT power modules. Based on the two different working conditions of the three-level NPC photovoltaic inverter, this paper has monitored the health status of bonding wires of the IGBT modules inside the inverter. In addition, for the experimental results of monitoring, theoretical analysis and experimental demonstration from the perspective of multi-physics (temperature field, electromagnetic field, etc.) are innovatively introduced, which provides a new perspective for the research of power module reliability.     

Enhanced power cycling performance of IGBT modules with a reinforced emitter contact

A typical emitter contact of an IGBT consists of a front metallization and bond wires. In this study, the power cycling performance of a special emitter contact design is experimentally verified. The emitter contact includes a metal plate, which is Ag-sintered to the metallization and wire bonded on the top surface. Either Cu or Al bond wires were implemented. Power cycling tests were performed to investigate the performance of such IGBT modules. The results were very promising and a cycling lifetime was achieved, which is about 20 times higher than the lifetime of typical IGBT modules. For a better understanding of the experimental results, the electrical and thermal response of the IGBT modules were simulated by FEM. The results of this study, provide a key for high-reliability designs of the emitter contact of IGBT modules with superior power cycling capability.     

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.     

Material requirements for high voltage, high power IGBT devices

The two basic package types of current IGBT modules, which evolved from opposing requirements of traction and power transmission applications, are presented. It is shown that reliability and lifetime aspects given by traction puts most stringent limitations on the choice of materials at given cost targets. The materials used today for high power packaging and the future developments of high power IGBT-packages are discussed.     

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

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.     

Envelop tracking based embedded current measurement for monitoring of IGBT and power converter system

Health monitoring of the power conversion system is very important. Therefore, we developed a new method for measuring IGBT currents and reproducing average load current to monitor IGBTs. This method was successfully tested on an experimental setup which showed that the tiny PCB sensors can be integrated into intelligent power modules. We proposed an inexpensive analogue circuit which is suitable for capturing current information from a tiny PCB Rogowski coil. The sensors and corresponding circuit can be embedded into an Intelligent Power Module. The method was named “Envelop tracking” as it simultaneously measures the currents of the high and low side switches of a power converter and reproduces the upper and lower edges of the load current which can be averaged by further digital processing.     

Tiny-scale “stealth” current sensor to probe power semiconductor device failure

“Stealth” electric current probing technique for power electronics circuits, power device modules and chips makes it possible to measure electric current without any change or disassembling the circuit and the chip connection for the measurement. The technique consists of a tiny-scale magnetic-field coil, a high speed analog amplifier and a digitizer with numerical data processing. This technique can be applied to a single bonding wire current measurement inside IGBT modules, chip scale current redistribution measurement and current measurement for surface mount devices. The “stealth” current measurement can be utilized in the failure mechanism understanding of power devices including IGBT short circuit destruction.     

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.     

New high power, high performance power converter systems

A new, high performance, low cost power converter system architecture is proposed. The system consists of a main converter and a multifunctional load conditioner. The main converter deals with most of the power flow running at a low switching frequency. The load conditioner is designed at a much lower power level running at a high-switching frequency. The load conditioner can (1) act like a current source and inject harmonic currents required by the load; (2) act like an active resistor to provide damping to the main converter; and (3) for three-phase inverters, decouple the coupling sources in the main inverter model in the rotating coordinates to make the control loop design for the main inverter much easier. The concept has been proved by simulation and experimental results on a 150 kW high performance three-phase utility power supply prototype. The proposed system configuration can be used in high power DC-DC converters, inverters, PFC and UPS applications     

宽频段大功率射频前端的设计问题

军用宽频段通信系统通常配置跳频滤波器以获得更好的抗干扰性能。这类系统的射频前端在发射时,易产生异常杂散。在大功率工作时,整机功率平坦度变差、定向耦合器产生额外谐波能量、跳频滤波器不仅表现为谐波抑制能力下降,还将导致邻信道功率比恶化。文中通过分析射频前端各模块级联后相互间的影响,以及各模块在通过大功率时特性的改变来阐明上述问题的原因,提出了相应的解决措施,这些措施在工程实践中已得到了有效应用。     

Analysis on the difference of the characteristic between high power IGBT modules and press pack IGBTs

The insulated gate bipolar transistor (IGBT) has been widely employed in such applications as alternate current motors and inverters for its lower driving power and lower on-state voltage. IGBT modules and press pack IGBTs are the most commonly used packaging for high-voltage and high-power-density applications. The difference in the packaging style and working conditions between IGBT modules and press pack IGBTs creates distinctions in, for instance, the thermal characteristics and reliability. Those distinctions lead to different applications and working conditions. In this paper, the development of IGBT devices has been reviewed, including the distinction of IGBT modules and press pack IGBTs in packaging style. Most importantly, the thermal and reliability characteristics have been compared in detail and the applications that are most suitable for IGBT modules and press pack IGBTs were outlined. The comparison of the thermal characteristics, reliability and applications provides guidance for users to take full advantage of the devices according to their requirements.     

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.     

Power cycling test and failure analysis of molded Intelligent Power IGBT Module under different temperature swing durations

Molded IGBT modules are widely used in low power motor drive applications due to their advantage like compactness, low cost, and high reliability. Thermo-mechanical stress is generally the main cause of degradation of IGBT modules and thus much research has been performed to investigate the effect of temperature stresses on IGBT modules such as temperature swing and steady-state temperature. The temperature swing duration is also an important factor from a real application point of view, but there is a still lack of quantitative study. In this paper, the impact of temperature swing duration on the lifetime of 600 V, 30 A, 3-phase molded Intelligent Power Modules (IPM) and their failure mechanisms are investigated. The study is based on the accelerated power cycling test results of 36 samples under 6 different conditions and tests are performed under realistic electrical conditions by an advanced power cycling test setup. The results show that the temperature swing duration has a significant effect on the lifetime of IGBT modules. Longer temperature swing duration leads to the smaller number of cycles to failure. Further, it also shows that the bond-wire crack is the main failure mechanism of the tested IGBT modules.     

一种新的梳状基区RF功率晶体管

给出一种新的 RF功率器件结构 -梳状基区结构 .在不增加本征集电结面积的情况下 ,该结构能显著改善 RF功率晶体管散热特性 ,增大器件的耗散功率和输出功率 ,较好地缓解了传统结构中高工作频率与大输出功率之间的矛盾 .模拟分析表明 ,采用该结构 ,器件的雪崩击穿电压能提高到理想平行平面结的 90 %以上 ,器件的大电流特性和频率特性也有所改进 .采用该技术制作的试验样管 DCT375同传统结构器件相比 ,其热电特性得到显著的改善 .这种结构为新型超高频、微波大功率管的研制开辟了新途径 .