Press-pack IGBT Research Articles

Study of pressure balance for Press-Pack IGBTs and its influence on temperature distribution

Pressure balance is a key technology for Press-Pack IGBT packaging, and is studied in this paper with its influence on the temperature distribution discussed in further when the device is turned on. By establishing the physical model of the Press-Pack IGBT device in the finite element simulation software, the influence of the internal flatness condition on the pressure balance is analyzed, and the variation of the average pressure difference with the flatness in different parallel scale of the chips is obtained. The thermal contact resistance and the electrical contact resistance parameters, which are dependent on the pressure, are then imported to perform the multi-field coupling, further investigating the effect of different pressure distributions on temperature distribution. The junction-case thermal resistance of the device with different flatness is compared experimentally. The results have demonstrated the influence of the flatness on the thermal resistance of the Press-Pack IGBT device.

Characterizations of a Proposed 3300-V Press-Pack IGBT Module Using Nanosilver Paste for High-Voltage Applications

Nanosilver paste was used in this study as a die-attachment material for 3300-V power chips to eliminate the pressure contact of a press-pack power module. The proposed insulated-gate bipolar transistor (IGBT) module was named as a sinter-pack IGBT module. We studied the effect of the assisted hydrostatic pressure, i.e., 0, 1, 3, 5, and 10 MPa, on the mechanical, thermal, and electrical performance of the as-sintered silver joints. As the pressure increased, the die-shear strength increased, and the thermal impedance decreased, as expected. The electrical properties of the assembly using the sintered silver were comparable with those of the chip with the same power rating, which proved the feasibility of the as-sintered IGBT specimens. The thermal resistance of the sinter-pack IGBT module decreased by 15.8% compared with that of the commercial press-pack one with the same power rating. The static electrical properties of the sinter-pack IGBT module were consistent with those of the commercial press-pack one, which further proved the feasibility of the sinter-pack IGBT module.

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.

Analysis of transient current distribution characteristics of Press Pack IGBT

In the switching process of Press Pack IGBT (PPI) module, the phenomenon of nonuniform current distribution invariably happens which reduce the reliability and life time of chips and the module. The uneven current distribution would be caused by some physical reasons such as the clamp force, the temperature; and the electrical reasons including the parasitic inductance of the emitter pillars, the parasitic resistance of the gate connector and the difference of the paralleled chips characteristic, etc. Based on the modeling of two disparate module structures, the parasitic parameter of the emitter pillars and gate connector is extracted in this paper. Then the different equivalent circuits of PPI module are built due to the researches in different factors with the Synopsys Saber software. At last, by comparing the influence of two modules indifferent factors, the simulation results prove the relationship between the pillars distribution and the chip switching losses.

Study on The Issue of Electric Field Concentration in Submodule of Press Pack IGBT

There is a phenomenon that the chips of press pack IGBT (Insulated Gate Bipolar Transistor) meet the requirements of withstand voltage test, but ignition sometimes occurred in the submodules of the same kind of press pack IGBT during the test. In response to this situation, this paper firstly analyzed that the difference of submodules frame lead to different level of electric field concentration. In this paper, quantitative conclusions have been drawed by modeling and simulation of the actual situation in COMSOL Multiphysics the multiphysics finite element simulation software.

Influence of Temperature on the Pressure Distribution Within Press Pack IGBTs

Press pack (PP) packaging technology has been applied to insulated-gate bipolar transistors (IGBTs) for high-voltage and high power density applications in recent years. The pressure distribution within PP IGBTs is very important because it affects both the electrical and thermal contact resistances, thermal cycling capability, and short-circuit current rating. Too much pressure will mechanically damage the chip and too little pressure will increase the thermal contact resistance, which eventually leads to chip thermal damage. In this paper, a finite-element multiphysics model cocoupled with an electrical field, thermal field, and mechanical field is proposed to analyze the collector current distribution, pressure distribution, and junction temperature distribution within PP IGBTs. The most important coupling variables, such as electrical and thermal contact resistances, for this cocoupled multiphysics model are calculated or measured by experiment through a single IGBT/fast-recovery diode chip submodule. Based on this multiphysics model, the influence of the high temperature generated by the chip's power dissipation on the pressure distribution within PP IGBTs (in the heating phase) is discussed, and then, compared with the pressure distribution in the clamping phase. The results show that the pressure distribution within PP IGBTs in the heating phase is extremely uneven and different from the value in the clamping phase. Furthermore, the mechanical model and its boundary conditions are verified through the pressure distribution experimental results in the clamping phase, which is measured based on the Fuji prescale film and the clamping test bench. Based on the simulation and experimental results, an optimization of the collector electrode and pedestal is proposed to improve the pressure distribution within PP IGBTs in the heating phase.

Study on the Method to Measure the Junction-to-Case Thermal Resistance of Press-Pack IGBTs

Accurate measurement of the junction-to-case thermal resistance of press-pack insulated gate bipolar transistors (PP IGBTs) is a great challenge due to their special packaging style and working conditions. The traditional thermocouple and transient dual interface methods have been successfully applied to measure the junction-to-case thermal resistance of wire-bonded IGBT modules. In this paper, a single fast-recovery diode (FRD) chip submodule is fabricated to determine the best method to measure the junction-to-case thermal resistance of PP IGBTs. Therefore, both the traditional thermocouple method and the transient dual interface method were used to measure the junction-to-case thermal resistance of the collector-side cooling with the emitter-side adiabatic. The transient dual interface method, which does not require locating a thermocouple to measure the case temperature, is ideal for the PP IGBTs measurement based on the experimental results and theoretical verification. Most importantly, both bulk thermal resistance of specific layers and thermal contact resistance between multilayers in PP IGBTs can be obtained by transforming the transient thermal-impedance curve.

Electric Field Analysis of Press-Pack IGBTs

High voltage IGBT module is the ideal option for the VSC-HVDC power transmission application. At present, wire-bonded technology and press-pack technology are available packaging technologies for high voltage IGBT. The press-pack IGBTs have such advantages as low inductance, low thermal impedance and short circuit failure mode than the wire-bonded IGBT module, which especially suit for high voltage power transmission application by series connection. However, the electrical insulation failure modes of press-pack IGBTs are much less known with limited literature published. In this paper, we presented the electric field analysis of a 3D press-pack IGBT model under DC rating voltage test condition. The electric field distribution of the press-pack IGBT stack was solved as an electrostatic problem by employing the finite element method. The results revealed the potential electrical insulation failure modes of the press-pack IGBTs: corona discharge at the edge of silver plate, partial discharge at the micro gap between die and PEEK frame and creeping discharge at the surface of PEEK frame.

Inductance extraction of Press-Pack IGBT by Considering Displacement Current

Taking the displacement current generated by charges accumulation into consideration, this paper presents a inductance extraction method for press-pack IGBT where conductor might not form a closed loop in simulation. Charge accumulating on ends of conductor is considered and then Ampere’s circuital law (ACL) could be meet. Vector potential A also could be affected by displacement current, which leads to a different formulation of partial inductance. A simplified model based on practical structure are used in numerical experiment for comparison between existing method and proposed method.

Cryogenic power electronics at megawatt-scale using a new type of press-pack IGBT

Electrical characteristics of a press-pack IGBT stack have been investigated experimentally in both static and dynamic tests at room temperature and at 77 K in an effort to identify a megawatt-scale class semiconductor that performs well electrically, thermally, and mechanically. It has been observed that the forward voltage drop and the turn-off time are both noticeably reduced at cryogenic temperatures, suggesting significant improvement in the device operating area. Furthermore, the stack was subjected to repeated thermal cycles between room temperature and 77 K without observing any degradation. A circuit simulation of a 200-kW boost converter based on the characterized press-back IGBT stack exhibited a reduction in switching and conduction losses at 77 K by 60% and 24%, respectively compared to the values at room temperature. It is expected that the type of press-pack IGBT stacks tested will be key elements to build high power dense, megawatt-scale cryogenic converters for future all-electric ships and electric airplanes.

Press-pack IGBTs for HVDC and FACTs

The popularity of insulated gate bipolar transistors (IGBTs) for use in high-voltage direct current (HVDC) transmission and flexible AC transmission systems (FACTS) is increasing. Unfortunately, for these applications wire-bond IGBT technology has a number of shortcomings, such as insufficient current ratings for the most powerful schemes, and inability to fail to short-circuit. Press-pack IGBT technology, conversely, offers increased current ratings, and an inherent short-circuit failure mode, making it a more attractive choice for HVDC and FACTS. However, the design and manufacture of these devices requires a comprehensive understanding of the unique technical challenges, which differ markedly from those for wirebond modules or traditional pressure contact devices. Specific challenges include providing a high degree of mechanical protection for the IGBT chip against normal operating stresses. Furthermore, it is essential to achieve uniform contact pressure across each chip surface to ensure optimum performance. To achieve this, manufacturers have designed products that use rigid copper electrodes manufactured to tighter tolerances than for other pressure contact devices, such as thyristors, and products that use compliant electrodes, incorporating spring assemblies. Dynex is in the advanced stages of development of press-pack IGBT technology with demonstrated robust solutions for the technical challenges outlined in this paper. Design success has been achieved through the use of state-of-the-art simulations in conjunction with a long history of manufacturing expertise for bipolar and IGBT products. Finally, multiple press-pack IGBT variants are currently undergoing evaluation tests prior to product release.

Evaluation of SiC Schottky Diodes Using Pressure Contacts

The thermomechanical reliability of SiC power devices and modules is increasingly becoming of interest especially for high-power applications, where power cycling performance is critical. Press-pack assemblies are a trusted and reliable packaging solution that has traditionally been used for high-power thyristor-based applications in FACTS/HVDC, although press-pack IGBTs have become commercially available more recently. These press-pack IGBTs require antiparallel PiN diodes for enabling reverse conduction capability. In these high-power applications, paralleling chips for high current conduction capability is a requirement, hence, electrothermal stability during current sharing is critical. SiC Schottky diodes not only exhibit the advantages of wide bandgap technology compared to silicon PiN diodes, but they have significantly lower zero temperature coefficient (ZTC), meaning they are more electrothermally stable. The lower ZTC is due to the unipolar nature of SiC Schottky diodes as opposed to the bipolar nature of PiN diodes. This paper investigates the implementation and reliability of SiC Schottky diodes in press-pack assemblies. The impact of pressure loss on the electrothermal stability of parallel devices is investigated.

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.

Study on the methods to measure the junction-to-case thermal resistance of IGBT modules and press pack IGBTs

The accurate measurement of the junction-to-case thermal resistance of Insulated Gate Bipolar Transistor (IGBT) devices is notably important for manufacturers to optimize the internal structure of packaging in order to improve its reliability and for users to take full advantage of the devices. The existing differences between IGBT modules and press pack IGBTs (PP IGBTs) not only in their packaging styles, but also in their working conditions may lead to some differences in the methods to measure their junction-to-case thermal resistance. In this paper, the junction-to-case thermal resistances of both IGBT modules and PP IGBTs have been measured using the traditional thermocouple method (steady-state method) and transient dual interface method (transient method). The applicability of these two methods for the measurement of junction-to-case thermal resistance of IGBT modules and PP IGBTs is summarized based on the experimental results. The steady-state method is suitable for the measurement of junction-to-case thermal resistance of IGBT modules, but not for PP IGBTs, because of the thermocouple inserted to measure the case temperature. The transient method is appropriate for the measurement of junction-to-case thermal resistance of not only IGBT modules, but also PP IGBTs, as a thermocouple is not required to measure the case temperature.

Optimization of the thermal contact resistance within press pack IGBTs

The research of thermal contact resistance between multi-layers within press pack IGBTs (PP IGBTs) is significant for optimizing the PP IGBTs' thermal resistance to improve reliability, as the thermal contact resistance accounts for approximately 50% of the total thermal resistance of PP IGBTs. In this paper, thermal contact resistance between multi-layers is analysed via a finite element model (FEM) of a single fast recovery diode (FRD) submodule. Most importantly, the influence of temperature and clamping force on the thermal contact resistance is also discussed, and findings are verified by submodule thermal resistance experiments. Based on the FEM and experimental results, nanosilver sintering technology is proposed to fill the gap between the contact interfaces to reduce thermal contact resistance. The fabrication of a sintered single FRD submodule is also investigated in this paper, and the results of the sintered sample indicate that the thermal resistance is reduced by approximately 18.8% compared to a direct contact sample.

Fault-tolerant design approach for reliable offshore multi-megawatt variable frequency converters

Inverters play a key role in realizing reliable multi-megawatt power electronic converters used in offshore applications, as their failure leads to production losses and impairs safety. The performance of high power handing semiconductor devices with high speed control capabilities and redundant configurations helps in realizing a fault-tolerant design. This paper describes the reliability modeling done for an industry standard, 3-level neutral point clamped multi-megawatt inverter, the significance of semiconductor redundancy in reducing inverter failure rates, and proposes methods for achieving static and dynamic redundancy in series connected press pack type insulated gate bipolar transistors (IGBT). It is identified that, with the multi megawatt inverter having 3+2 IGBT in each half leg with dynamic redundancy incorporated, it is possible to reduce the failure rate of the inverter from 53.8% to 15% in 5 years of continuous operation. The simulation results indicate that with dynamic redundancy, it is possible to force an untriggered press pack IGBT to short circuit in <1s, when operated with a pulse width modulation frequency of 1kHz.

Loss Analysis and Comparison of High Power Semiconductor Devices in 5MW PMSG MV Wind Turbine Systems

This paper provides a loss analysis and comparison of high power semiconductor devices in 5MW Permanent Magnet Synchronous Generator (PMSG) Medium Voltage (MV) Wind Turbine Systems (WTSs). High power semiconductor devices of the press-pack type IGCT, module type IGBT, press-pack type IGBT, and press-pack type IEGT of both 4.5kV and 6.5kV are considered in this paper. Benchmarking is performed based on the back-to-back type 3-level Neutral Point Clamped Voltage Source Converters (3L-NPC VSCs) supplied from a grid voltage of 4160V. The feasible number of semiconductor devices in parallel is designed through a loss analysis considering both the conduction and switching losses under the operating conditions of 5MW PMSG wind turbines, particularly for application in offshore wind farms. This paper investigates the loss analysis and thermal performance of 5MW 3L-NPC wind power inverters under the operating conditions of various power factors. The loss analysis and thermal analysis are confirmed through PLECS Blockset simulations with Matlab Simulink. The comparison results show that the press-pack type IGCT has the highest efficiency including the snubber loss factor.

On the Potential of IGCTs in HVDC

In today’s voltage source converter HVDC solutions, insulated-gate bipolar transistors (IGBTs) are used exclusively, generally in module form where the modular multilevel converter is concerned; this entails a number of protective measures that increase complexity and cost. As we move to higher transmitted powers, the use of integrated gate-commutated thyristors (IGCTs) would allow both higher voltages and currents while simultaneously reducing losses, failure rates, and costs, as this paper tries to demonstrate by comparing current production IGCTs with both current module and press-pack IGBTs.

Possible failure modes in Press-Pack IGBTs

Reliability of Press-Pack IGBTs is a topic with limited published data and information. This paper presents results of a power cycling test with state-of-the-art high power devices. An accelerated lifetime test scheme was defined, and six out of eight devices were tested until failure. A microscopy analysis has been performed on some of the failed devices, and they have all failed in a very similar manner. In order to gain additional information about the thermal–mechanical stress, a detailed 3D Finite Element Method (FEM)-analysis has been conducted. The combined results from power cycling, microscopy and FEM have been concluded to two possible failure modes in Press-Pack IGBTs: Gate oxide damage and micro arcing.

Electro-Thermo-Mechanical Analysis of High-Power Press-Pack Insulated Gate Bipolar Transistors under Various Mechanical Clamping Conditions

Electro-Thermo-Mechanical Analysis of High-Power Press-Pack Insulated Gate Bipolar Transistors under Various Mechanical Clamping Conditions