IGBT Chip Research Articles

Evaluation of Frequency and Temperature Dependence of Power Losses Difference in Parallel IGBTs

With the development of high power converters, safe operation of IGBT modules with parallel chips is of increasing importance. IGBT can work normally in safe range in the initial operation even if current imbalance is happening. However, if the uneven current state lasts too long, it is difficult to keep a uniform junction temperature, which can further lead to uneven distribution of the power losses. In severe cases, the device and converter may be damaged due to overheating. This paper studies the stability of such an interactive process with mathematical modelling backed by experiment. Because of the opposite sensitivities of switching and conduction losses to temperature under high current injection, the concept of `inflection point frequency characteristic' is introduced to evaluate the trend of junction temperature mismatches between the parallel IGBT chips. The inflection point frequency at different current and temperature levels is tested to verify the model prediction, and the applicability of this approach in multi-chip parallel module is discussed. By establishing the relationship between the switching frequency and the thermal stability limit of parallel IGBTs, it can provide a feasible reference for improving the reliability of multi-chip parallel power devices.

Gate–Emitter Pre-threshold Voltage as a Health-Sensitive Parameter for IGBT Chip Failure Monitoring in High-Voltage Multichip IGBT Power Modules

This paper proposes a novel health-sensitive parameter, called the gate-emitter pre-threshold voltage VGE(pre-th), for detecting IGBT chip failures in multichip IGBT power modules. The proposed method has been applied in an IGBT gate driver and measures the VGE at a fixed time instant of the VGE transient before the threshold voltage occurs. To validate the proposed method, theoretical analysis and practical results for a 16-chip IGBT power module are presented in the paper. The results show a 500 mV average shift in the measured VGE(pre-th) for each IGBT chip failure.

Research on Modeling Simulation and Parameters Extraction of IGBT

IGBT is the key component of electric vehicle motor control system. In order to control IGBT and motor accurately and effectively, the structure of MOSFET and N-IGBT is given based on semiconductor principle. The four-layer PNPN structure of IGBT is analyzed. The equivalent circuit model of IGBT based on MOSFET, PNP and NPN transistor is established. Combining with Infineon IGBT chip and its application data, the collector current transmission characteristic curves under different gate source voltages and environment temperature are given. The simulation method of the same characteristic curves can be obtained by setting IGBT micro-variable equivalent circuit model parameters using Q3D and Simplorer. The model parameters such as parasitic capacitance, parasitic inductance, junction resistance and so on of the IGBT chip are determined and extracted. Thus the accurate model of IGBT chip is established. The simulation results show that the modeling and parameters extraction methods can effectively extract the precise parameters of IGBT, and can provide precise data for the analysis and establishment of the equivalent circuit model of IGBT.

A 3D Thermal Network Model for Monitoring Imbalanced Thermal Distribution of Press-Pack IGBT Modules in MMC-HVDC Applications

In this paper, the impact of a double-sided press-pack insulated-gate-bipolar-transistor (PP IGBT) cooling structure on its thermal impedance distribution is studied and explored. A matrix thermal impedance network model is built by considering the multi-chip thermal coupling effect for the collector side of the PP IGBT. Moreover, a verification has been made by comparing the proposed matrix thermal network model and the conventional lumped RC network model provided by the manufacturer. It is concluded that the collector side has lower thermal resistance and dissipates about 88% of the heat generated by the IGBT chips inside the module. Then, a modular-multilevel-converter high-voltage-direct-current (MMC-HVDC)-based type test setup composed of the press-pack IGBT stacks is established and the junction temperature is calculated with the proposed thermal model and verified by temperature measurements.

Modeling and Analysis on Overall Fatigue Failure Evolution of Press-Pack IGBT Device

Press-pack insulated-gate bipolar transistor (PP-IGBT) device is used in high-power modular multilevel converter high-voltage direct current (MMC-HVDC) system due to the advantages of high reliability and short-circuit failure. Considering safeties and stable operations, it is necessary to model and analyze the fatigue failure evolution of PP-IGBT device that improves the reliability of MMC-HVDC system. This paper proposes a method to analyze from fretting wear failure to short-circuit failure in PP-IGBT device. First, a multiphysics coupling model of a single-chip 3.3-kV/50-A PP-IGBT device is presented to analyze the fretting wear failure, and the weak layer and the fatigue effect are obtained by power cycling simulation. Second, considering the Al-Si diffusion reaction mechanism on the interface of IGBT chip, the short-circuit failure is investigated by the finite-element method model of PP-IGBT device with Al-Si osmotic hole, and the changing trend of characteristic parameters is estimated during short-circuit failure process. Finally, the steady state, power cycling, and short-circuit tests are used to verify the multiphysics coupling model, fretting wear failure, and short-circuit failure. The experiment indicates that the fatigue failure evolution of PP-IGBT device occurs from fretting wear failure to short-circuit failure, and it suggests that the proposed method can be applied to optimize design and condition monitoring of PP-IGBT device.

Influence of the clamping force on the power cycling lifetime reliability of press pack IGBT sub‐module

The clamping force is the most important parameter of Press Pack IGBTs (PP IGBTs) as it not only affects the electrical, thermal, and mechanical characteristic, but also the long lifetime reliability. Too little clamping force increases the contact resistance and junction temperature. Too much clamping force makes the silicon chips mechanical damage. However, it is quite complex and time-consuming to obtain the influence of the clamping force on the long-time reliability through the power cycling test because that many tests are needed to execute under a large range of clamping forces. Here, a single IGBT chip sub-module is proposed to simulate the long lifetime reliability through the finite element method under various clamping forces. Both the thermal contact resistance within different contact interfaces that affects the junction temperature of silicon chips a lot and the elastic-plastic model that affects the lifetime of specific material layers are considered in this finite element model to make it more accurate. The combination of Coffin–Mason and Basquin model is proposed to obtain the power cycling lifetime of the sub-module based on simulation results. A clamping force range is obtained and this also gives a guideline for the power cycling test.

Study on the Cauer Thermal Network Model of Press Pack IGBTs

Press Pack IGBTs (PP IGBTs) has been gradually applied in the high voltage and high current areas, for its high power density, double side cooling and high reliability. The cauer thermal network model of PP IGBTs is proposed based on the boundary effect according to heat spreading angle in this paper, and the difference between the IGBT and FRD chips is considered in this model. The thermal contact resistance among multi-layers within PP IGBTs, which is calculated and corrected by the experiment, is also included in this model. The finite element method (FEM) model is used to verify the accuracy of the cauer model, because the accurate measurement of the junction to case thermal resistance of PP IGBTs is extremely difficult. The thermal characteristic of PP IGBTs under different clamping force can be acquired through the cauer thermal model. It has significant influence on the thermal resistance optimization, as the thermal resistance percentage of the components in PP IGBTs can be obtained from the cauer thermal model.

What Happens to Low TCE Copper with Annealing

Introduction Since the Copper resistivity is second lowest next to the Silver, the Copper electrodeposits have been very intensively used in the wiring for the semiconductor and the printed circuit board (PCB). The Copper problem is the thermal coefficient of expansion (TCE). The Silicon is 2.6x10-6 (1/K) and the copper is 17x10-6 (1/K). If the composite of the Silicon and the Copper (semiconductor and PCB), warpage, protrusion or delamination occurs. Warpage, protrusion or delamination resolution by low TCE copper examples are reported. Results TSV no pumping at 450oC. Crack and Copper extrusion occurs at bottom corner of conventional Copper TSV. No crack and no Copper extrusion occurs for our low TCE Copper (Fig.1).No glass crack with 180oCx1hr for the glass interposer.The Copper wiring for the IGBT wafer shows half warpage and no warpage at 350oC.The coreless PCB warpage reduce to half.No crack between the ceramics and the copper or Copper wire and IGBT chip in reliability test (Under examination).No crack in via for via on via stacking for the buildup PCB (Under examination). Reference Q. Dinh and K. Kondo, ECS J. Solid State Sci. Technol., 6, P566–P569 (2017). Figure 1

Simulation Study of Overcurrent Turn-off Capability in 4500V IGBT

According to the requirement of IGBT's over-current turn-off capability, this paper analyzes the factors affecting the dynamic latch-up of IGBT chip during the over-current turn-off process, including the gate width of IGBT cell, the doping concentration of back P + collector and the dVce/dt when the IGBT is turned off. The simulation results show that the anti-dynamic latch-up capability of IGBT can be effectively improved by decreasing the gate width and back P + collector doping concentration. Through multi-cell parallel simulation, it is found that current concentration exists in the process of overcurrent trun-off, which leads to the further increase of the lattice temperature, and the overcurrent turn-off capability declines.

16-Channel micro magnetic flux sensor array for IGBT current distribution measurement

Current crowding of IGBT and power diode in a chip or among chips is a barrier to the realization of highly-reliable power module and power electronics system. Current crowding occurs because of the parasitic inductance, difference of chip characteristics or temperature imbalance among chips. Although current crowding among IGBT or power diode chips has been analysed on numerical simulations, no sensor with sufficiently high special resolution and fast measurement time has yet been demonstrated. Therefore, the author developed and demonstrated 16-channel flat sensitivity sensor array for IGBT current distribution measurement. The sensor array consists of tiny-scale film sensors with analog amps and shield case against noise. The array and digital calibration method will be applied for reliability analysis, designing and screening of IGBT modules.

IGBTs working in the NDR region of their I-V characteristics

This paper demonstrates the detailed work on high voltage IGBTs using simulations and experiments. The current-voltage characteristics were measured up to the break through point in forward bias operating region at two different temperatures for a 50 A/4.5 kV rated IGBT chip. The experimentally measured data were in good agreement with the simulation results. It was also shown that the IGBTs are able to clamp high collector-emitter voltages although a low gate turn-off resistor in combination with a high parasitic inductance was applied. Uniform 4-cell and 8-cell IGBT models were created into the TCAD device simulator to conduct an investigation. An engendered filamentation behaviour during short-circuit turn-off was briefly reviewed using isothermal as well as thermal simulations and semiconductor approaches for development of filaments. The current filament inside the active cells of the IGBT is considered as one of the possible destruction mechanism for the device failure.

A study on IGBT junction temperature (Tj) online estimation using gate-emitter voltage (Vge) at turn-off

A novel method is presented for online estimation of the junction temperature (Tj) of semiconductor chips in IGBT modules, based on evaluating the gate-emitter voltage (Vge) during the IGBT switch off process. It is shown that the Miller plateau width (in the Vge waveform) depend linearly on the junction temperature of the IGBT chips. Hence, a method can be proposed for estimating the junction temperature even during converter operation – without the need of additional thermal sensors or complex Rth network models. A measurement circuit was implemented at gate level to measure the involved time duration and its functionality was demonstrated for different types of IGBT modules. A model has been proposed to extract Tj from Vge measurements. Finally, an IGBT module with semiconductor chips at two different temperatures has been measured using Vge method and this method was found to provide the average junction temperature of all the semiconductor chips.

Distributed electro-thermal model of IGBT chip – Application to top-metal ageing effects in short circuit conditions

A new distributed electro-thermal model has been developed in order to analyze electrical and thermal mappings of power devices during critical operations. The model is based on dividing power device into a vertical multilayer structure, with each layer discretized into multiple slab volumes. This model has been used to evaluate the effects of chip metallization ageing on temperature distributions and current sharing between cells within an IGBT chip during short-circuits operations. Dynamic latch-up failures during short-circuit operations has been investigated.

IGBT chip current imaging system by scanning local magnetic field

An IGBT/power diode current distribution imaging system was demonstrated. This system can capture current redistribution or oscillation inside or among chips on a DBC-level sub-module. It can perform failure analysis of power semiconductors by detecting problems such as nonuniform current distribution between bonding wires. The system scans the chip’s shape using a laser sensor and then records the local magnetic field near the bonding wire using a 4-axis robot coil sensor. The coil sensor has two pair of Cu patterned spiral coils symmetrically arranged on both sides of a 60-μm-thick polyimide film. The system enables the analysis of destructive current concentrations of the entire chip, among chips or a part of the chip under high current or high voltage switching conditions, without making any changes or disassembling the chip connections.

Reverse-Conducting IGBT Using MEMS Technology on the Wafer Back Side

In this paper, we present a 600-V reverse conducting insulated gate bipolar transistor (RC-IGBT) for soft and hard switching applications, such as general purpose inverters. The newly developed RC-IGBT uses the deep reactive-ion etching trench technology without the thin wafer process technology. Therefore, a freewheeling diode (FWD) is monolithically integrated in an IGBT chip. The proposed RC-IGBT operates as an IGBT in forward conducting mode and as an FWD in reverse conducting mode. Also, to avoid the destructive failure of the gate oxide under the surge current and abnormal conditions, a protective Zener diode is successfully integrated in the gate electrode without compromising the operation performance of the IGBT.

Investigation of self-similar heat sinks for liquid cooled electronics

Electronic systems require cooling devices that are able to deal with high heat-flux capabilities. For this purpose, microchannels are attractive for direct cooling, due to their superior performances. A study on self-similar heat sinks for liquid cooled electronics is presented in this work, where the devices are made from copper, designed for industrial application and for large scale production. Self-similarity refers to the fact that there is a certain similarity and repeatability (or pattern) of the substructures compared with the overall structure. The internal structures, the so called overflow structures (or microchannels), have been designed in order to achieve high heat transfer coefficients. To validate the design and describe the flow characteristics inside the device via analytical solutions is almost impossible, therefore a well known numerical code was employed to have an insight of the thermal-fluid distributions. As can be seen clearly from the simulation, most of the heat is removed in the overflow-structure, on the side of the device adjacent to the source of heat. This paper attempts to analyse a comprehensive list of data as well as plots in a critical manner in order to illustrate the significant characteristics of this type of device. A clear lack in a proper common definition of the heat flux may lead to a misinterpretation of the results, in fact depending on the chosen area where the heat exchange takes place (namely the internal area of the microstructures or the separation surface between the device and the heating source), we can achieve a maximum heat flux of either about 200 W/cm2 or about 700 W/cm2. A very low pressure drop together with a good heat removal capability, make this device suitable for cooling of IGBT chips in power electronic applications.

Evaluation of IGBT thermo-sensitive electrical parameters under different dissipation conditions – Comparison with infrared measurements

Junction temperature evaluation is a key parameter used to control a power module assembly. But measuring the junction temperature by thermo-sensitive electrical parameters (TSEPs) does not reveal the actual temperature of the semiconductor device. In this paper, a specific electronic board used to compare four common TSEPs of IGBT chips is presented. For this comparison, two dissipation modes are used: dissipation in active and saturation regions. In order to have referential measurements we carried out surface temperature measurements of IGBT chips with an infrared (IR) camera. A dedicated numerical tool is presented to estimate the mean surface temperature of active region. In the case of a single IGBT chip, the comparison between IR and TSEP measurements show that the best studied parameter (in terms of robustness and usability) is the gate emitter voltage.

Large-area Nanosilver Die-attach by Hot-pressing Below 200°C and 5 MPa

Sintered nanoscale silver joint is an emerging lead-free die-attach solution for high-temperature packaging because of silver's high melting temperature. For bonding small chips, the nanosilver solution can be achieved with a simple heating profile under atmospheric pressure. However, for bonding large-area chips, e.g. > 1 cm2 IGBT chips, uniaxial pressure of a few MPa has been found necessary during the sintering stage of the bonding process, which is carried out at temperatures below 275°C. Hot-pressing at high temperatures can cause significant wear and tear on the processing equipment, resulting in high maintenance cost. In this study, we ran a series of experiments aimed at lowering the hot-pressing temperature. Specifically, we examined a process involving hot-press drying, followed by sintering without any applied pressure. A fractional factorial design of experiments was used to identify the importance and interaction of various processing parameters, such as hot-pressing pressure/temperature/time and sintering temperature/time, on the final bond quality of sintered nanosilver joints. Based on the results, a simpler process, consisting of hot-press drying at 180°C under 3 MPa, followed by sintering at 275°C under atmospheric pressure was found to produce attachments with die-shear strength in excess of 30 MPa.

Development of a low‐noise IGBT module

AbstractHigh‐frequency leakage current that may cause serious conducted EMI problems flows through an inverter system. The paths of the leakage current are stray capacitances that are formed inside of motors, cables, and IGBT modules. This paper proposes a new IGBT module that realizes low conducted emission noise by flipping the IGBT chip of the lower‐voltage side to decrease its stray capacitance. The leakage current flowing through the low‐noise IGBT module becomes small, since the stray capacitance is a main path of the current. Through an experiment, it is clarified that the conducted emission level is reduced by 13 dB at a maximum when the low‐noise IGBT module is applied to a resonant‐type inverter. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(4): 45–52, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20971

IGBT module failure analysis in railway applications

This work reports two different characteristic patterns detected in IGBT chips failed in real operation (railway application) by failure analysis procedures. The analysed chips have been recovered from the rheostatic chopper leg and from the three legs which supplies the traction motor. It is observed that depending on the location and characteristics of the detected default (burn-out spot), this failure can be attributed to a latch-up process or a secondary breakdown mechanism. These results are corroborated with tests at limit, obtaining the same result. Consequently, each failure can be linked to overcurrent (latch-up) or overtemperature (secondary breakdown) events, which makes possible to distinguish between problems coming from driving strategies or thermal issues (uneven temperature distribution inside the module or packaging wear-out).