Silicon Carbide Power Module Research Articles

Characterization of PCB Embedded Package Materials for SiC MOSFETs

In this paper, a novel fan-out panel-level printed circuit board (PCB) embedded package technology for silicon carbide (SiC) MOSFET power module is presented to address parasitic inductances, heat dissipation, and reliability issues that are inherent with aluminum wires used in conventional packaging scheme. To withstand high temperature beyond 175 °C and high voltage over 1.2 kV and improve thermomechanical reliability of the fan-out panel-level PCB embedded SiC power module, bismaleimide-triazine (BT) laminate and prepreg with high-temperature stability, high dielectric strength, coefficient of thermal expansion (CTE) matching with SiC, and high $T_{g}$ are selected as PCB embedded package materials. Then, high-temperature stabilities, dielectric breakdown strength, and thermomechanical performances of the embedded materials are characterized. The experimental results show that the PCB embedded materials can withstand high temperature beyond 200 °C and a high voltage above 1.2 kV. $T_{g}$ is as high as over 260 °C, and CTE is matching with SiC. Besides, in order to provide one guideline for the high-temperature and high-pressure laminating process during the PCB embedded SiC MOSFETs packaging, cure kinetics of BT prepreg are analyzed. The results show that 1-h curing time at 280 °C curing temperature and 2-h curing time at 210 °C curing temperature can ensure the full cure of the BT prepreg.

Comparison of High Voltage SiC MOSFET and Si IGBT Power Module Thermal Performance

Silicon carbide (SiC) devices have been gradually applied in power electronic for the characteristics of high voltage, high power densities, elevated operating temperature and low switching energy loss. In this paper, a SiC MOSFET welding power module is proposed based on high voltage Si IGBT standard module structure to evaluate the thermal performance. The thermal lateral spread model expounds the expansion of the heat flow in the vertical crossing of a thermal conductor, and thermal resistance distributions of packaging materials in Silicon carbide and Silicon power module are studied through the COMSOL Multiphysics finite element software based on the thermal lateral spread model assumption that minute changes in thermal conductivity would produce no alterations in heat spreading angle. The result indicate that SiC MOSFET module gives the larger thermal resistance than the Si IGBT module with the same encapsulation structure but higher power densities for SiC, what’s more, the solder for die attach and direct bonding copper which include upper copper, substrate and lower copper contribute more thermal resistance in SiC MOSFET module. The differences of thermal Performance in SiC and Si modules can be obtained to benefit us in optimizing SiC MOSFET power module structure design and packaging materials selection.

Reliability Evaluation of SiC Power Module With Sintered Ag Die Attach and Stress-Relaxation Structure

Silicon carbide (SiC) power modules with Ag sinter-bonding die attach were designed on the basis of thermal stress analysis for reliable high-temperature operations. Both the finite-element analysis (FEA) simulations and preliminary experiments confirmed that inserting the direct-bonded-copper (DBC) substrates can effectively reduce the maximum thermal stress in the module. A prototype SiC power module using sintered Ag die attach with a DBC substrate was designed and fabricated. The modules exhibited excellent durability in power cycling between 65 °C and 250 °C up to 20 000 cycles. FEA calculations of cumulative thermal strain and stress distributions adequately predicted the initial cracking position in the specimens after prolonged power cycles, observed by scanning electron microscopy.

Electrical Performance Advancement in SiC Power Module Package Design With Kelvin Drain Connection and Low Parasitic Inductance

Silicon carbide (SiC) power modules are promising for high-power applications because of the high breakdown voltage, high operation temperature, low ON-resistance, and fast switching speed. However, the large parasitic inductance in existing package designs results in compromised performance, i.e., long blanking time in the desaturation protection scheme and large overvoltage spikes during the switching transient. Consequently, the benefits of SiC devices are often not fully utilized in practical applications. This paper deals with these two issues and aims at improving the electrical performance of the existing SiC module package. Specifically, a package design with Kelvin drain-to-source connection is first proposed to minimize the blanking time. More than 99% reduction of blanking time is achieved experimentally compared to the conventional package design. Second, a low parasitic inductance package with double-side cooling is proposed to allow the fast switching speed of SiC devices without sacrificing the thermal performance. A power loop inductance of 1.63 nH is realized from Q3D simulation. Verified by the experiment, more than 60% reduction of power loop inductance is achieved in comparison to a previously designed baseline module. At 0- $\Omega $ external gate resistance, the turn-off voltage spike is less than 9% of the dc-link voltage under the rated load condition.

Electrical Performance and Reliability Characterization of a SiC MOSFET Power Module With Embedded Decoupling Capacitors

Integration of decoupling capacitors into silicon carbide (SiC) metal oxide semiconductor field effect transistor ( mosfet ) modules is an advanced solution to mitigate the effect of parasitic inductance induced by module assembly interconnects. In this paper, the switching transient behavior is reported for a 1.2-kV SiC mosfet module with embedded dc-link capacitors. It shows faster switching transition and less overshoot voltage compared to a module using an identical package but without capacitors. Active power cycling and passive temperature cycling are carried out for package reliability characterization and comparisons are made with commercial Si and SiC power modules. Scanning acoustic microscopy images and thermal structure functions are presented to quantify the effects of package degradation. The results demonstrate that the SiC modules with embedded capacitors have similar reliability performance to commercial modules and that the reliability is not adversely affected by the presence of the decoupling capacitors.

Analysis of Ultrasonic Welding of Mechanically Coupled Small Area Contacts for a Silicon Carbide Power Module

Abstract In this paper, the shear strength of small-area welded contacts was optimized. Using design of experiments (DoE) optimization techniques, copper power contacts with 4 mm2 feet were welded to both copper and nickel/gold-plated copper substrates where pressure, amplitude and deformation were the control factors. For the DoE, the setting combinations were chosen based on the concept of classical Screening Design. This design was best suited because it allowed an elementary exploration of interaction relationships for a wide range of factors. The pressure was varied from 1.4 to 1.8 bar, the amplitude from 90 to 100%, and the deformation from 0.06 to 0.1 mm. These limits were chosen based on prior welding experience with the equipment and similar parts. Each bond was optically inspected to confirm high-quality bonds. Using common shear techniques, over 200 bonds were sheared; strengths were recorded as the DoE dependent variable. The initial step found that pressure was the most significant factor. Pressure and deformation were also proven to affect strength inversely to each other. Interestingly, the planarity of the contacts had no measurable effect on the welding strength. Consistent bond strengths were achieved regardless of the bonds' place within the established bond order. For both copper-to-copper and copper-to-nickel/gold-plated bonds, the optimal settings were: pressure at 1.8 bar, amplitude at 90%, and deformation of 0.1 mm, while achieving shear strengths of 40.5 kgf and 39.1 kgf, respectively. This doubled the previous benchmark weld strengths.

Experimentally validated methodology for real-time temperature cycle tracking in SiC power modules

The ability to monitor temperature variations during the actual operation of power modules is key to reliability investigations and the development of lifetime prediction strategies. This paper proposes an original solution, specifically devised with novel fast-switching silicon carbide (SiC) power MOSFETs in mind. The results show ability to track temperature variations resulting from active power cycling of the devices, including high speed transients, thus enabling to discriminate among different potential failure mechanisms. Validation of the proposed methodology and its accuracy is carried out with the support of infrared thermography.

Review of Thermal Packaging Technologies for Automotive Power Electronics for Traction Purposes

Due to its superior electrical and thermal characteristics, silicon carbide power modules will soon replace silicon modules to be mass-produced and implemented in all-electric and hybrid-electric vehicles (HEVs). Redesign of the power modules will be required to take full advantage of these newer devices. A particular area of interest is high-temperature power modules, as under-hood temperatures often exceed maximum silicon device temperatures. This review will examine thermal packaging options for standard Si power modules and various power modules in recent all-electric and HEVs. Then, thermal packaging options for die-attach, thermal interface materials (TIM), and liquid cooling are discussed for their feasibility in next-generation silicon carbide (SiC) power modules.

Study of Baseplate Materials for High-Temperature Operation of SiC Power Modules

Baseplate materials used for the high-temperature operation of silicon carbide (SiC) power modules must have mechanical properties suitable for maintaining the reliability of solder joints. In addition, to efficiently dissipate heat generated from a SiC device, superior thermal specifications are required for the baseplate material. In this study, we investigated the mechanical properties of the baseplate materials using finite element method (FEM)simulation and thermal-deformation observation. Thus, we showed that the shear stress at a solder joint can be reduced by using aluminum–carbon (AlC) or copper–molybdenum–copper (CMC)baseplates, both of which have a low value of Young’s modulus.We also measured the steady-state and transient thermal resistances of these materials and showed that CMC baseplate has superior thermal properties. In this study, we showed that among the baseplate materials that were studied, the CMC baseplate is optimal for the high-temperature operation of SiC power modules.

Development of High Temperature Operation SiC Power Module

We have developed a Silicon Carbide (SiC) power module that can operate at high temperatures up to 250 °C. Figure 1 shows the overview of the developed power module. The withstand voltage of the power module is 1200 V, two SiC - MOSFETs are built in, and it is a circuit composition of one phase of the power inverter. The two-layer SiC-Active Metal Brazed Copper(AMC) not only reduces the area of the power module but also reduces circuit inductance. In addition, this power module has a built-in snubber circuit that reduces the switching surge voltage of the SiC-MOSFET during high-speed switching. Generally, when the power module is operated at a high temperature, the reliability such as occurrence of lowering of the main bonding strength of the power module is significantly reduced due to thermal deformation. In this power module, the main components of the module are joined using eutectic solder with a solidus line above 350 °C. Copper-tungsten (CuW) was selected as the base plate material. Since the Coefficient of Thermal Expansion (CTE) values of CuW and SiN - AMC are close, it is possible to reduce the stress applied to these joints when the temperature changes. In addition, CuW has excellent thermal conductivity and heat capacity and suppresses heat generation of SiC-MOSFET. To evaluate the performance of this module, a switching test at 100 A was performed at 250 °C. The switching waveform is shown in Fig.2. The turn-off switching time tf was about 10 ns, and the switching surge voltage at that time was about 150 V. The turn-off switching waveform was almost the same from room temperature to 250 °C. As a result, it was shown that this power module can operate at 250 °C and the built-in snubber circuit works effectively at all temperatures. Acknowledgement This work was supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), "Next-generation power electronics / Consistent R&D of next-generation SiC power electronics" (funding agency: NEDO). Figure 1

The Development of High Thermal Conductivity SiC Power Modules through the Implementation of Advanced Cooling Techniques Coupled with High Heat Transfer Materials

This paper discusses Wolfspeed’s advances in silicon carbide (SiC) power module packaging, focusing on recent developments in advanced power module heat transfer techniques, the integration of pinfin mechanical structures, and the implementation of advanced die attach materials. Heat spreader materials and novel cooling methods suitable for SiC power modules are presented, focusing on the thermal heat transfer properties and a discussion of the design and prototype experimental impacts.

First Demonstration of High Temperature SiC CMOS Gate Driver in Bridge Leg for Hybrid Power Module Application

A high-temperature silicon carbide power module using CMOS gate drive technology and discrete power devices is presented. The power module was aged at 200V and 300 °C for 3,000 hours in a long-term reliability test. After the initial increase, the variation in the rise time of the module is 27% (49.63ns@1,000h compared to 63.1ns@3,000h), whilst the fall time increases by 54.3% (62.92ns@1,000h compared to 97.1ns@3,000h). The unique assembly enables the integrated circuits of CMOS logic with passive circuit elements capable of operation at temperatures of 300°C and beyond.

Identification of thermo-mechanical fatigue fracture location by transient thermal analysis for high-temperature operating SiC power module assembled with ZnAl eutectic solder

Abstract In this paper, we demonstrate that the structural degradation of a silicon carbide (SiC) power module corresponding to thermal cycles can be detected and tracked non-destructively by transient thermal analysis method. The purpose of this evaluation is to analyze the distribution of the thermal resistance in the power module and to identify the structure deterioration part. The power module with SiC-MOSFET were assembled using ZnAl eutectic solder as device under test. The individual thermal resistance of each part such as the SiC-die, the die-attachment, the AMCs, and the baseplate was successfully evaluated by analyzing the structure function graph. A series of thermal cycle test between −40 and 250°C was conducted, and the power modules were evaluated their thermal resistance taken out from thermal cycle test machine at 100, 200, 500 and 1000 cycles. We confirmed the increase in thermal resistance between AMCs and base plate in each thermal cycle. The portion where the thermal resistance increased is in good agreement with the location of the structural defect observed by scanning acoustic tomography (SAT) observation.

Transient thermal characteristics of high-temperature SiC power module enhanced with Al-bump technology

In this paper, we demonstrate a mounting technology that improves the tolerance to transient power loss by adding a heat capacity near the device. Silicon carbide (SiC) power devices can operate at high temperatures, up to 250 °C, at which silicon (Si) power devices cannot. Therefore, it is possible to allow a large temperature difference between the device and ambient air. Thus, the size of a power converter equipped with an SiC power module is reduced by simplifying the cooling system. The temperature of the power module is important not only in the steady state, but in transient loads as well. Therefore, we developed the Al-bump flip-chip mounting technology to increase heat capacity near the device. With this proposed structure, the heat capacity per device increased by 1.7% compared with the total heat capacity of the conventional structure using wire bonding. The reduction in transient thermal impedance is observed from 0.003 to 3 s, and we confirmed that the transient thermal impedance is reduced very efficiently by 15% at the maximum, compared with the conventional structure.

Miniature Piezoelectric Sensor for In-Situ Temperature Monitoring of Silicon and Silicon Carbide Power Modules Operating at High Temperature

Owing to the introduction of wide-bandgap power devices, recent power modules operate at higher temperatures. This increased module temperature leads to significant reliability problems, which render thermal monitoring very important. Several thermal sensors have been used in power modules; however, each of these sensors has drawbacks such as limited maximum temperature, nonlinearity, power source requirement, or limited miniaturization. This paper proposes a new temperature sensor that utilizes the piezoelectric effect. A new piezoelectric material (PZT-PZNM) with a high Curie temperature (260 °C) is soldered onto a direct bonded copper substrate. When the power module is operating at a high temperature, the substrate deflects and induces thermal stress, which is converted into an electric voltage via a piezoelectric mechanism. The voltage can be maximized by optimizing the location of the PZT-PZNM; the best location was determined to be away from the power devices. This observation confirms that the piezoelectric temperature sensor has a negligible influence on the performance of the power devices. Moreover, the sensor volume was miniaturized (approximately 74% reduction compared with preliminary work) to ensure that it can be readily integrated into power modules. The developed piezoelectric sensor demonstrates excellent linearity ( R 2 = 0.99, approximately) up to 250 °C, which is sufficient for monitoring temperature in both silicon and silicon carbide power modules.

Failure and Reliability Analysis of a SiC Power Module Based on Stress Comparison to a Si Device

The superior electro-thermal properties of silicon carbide (SiC) power devices permit higher temperature of operation and enable higher power density compared with silicon devices. Nevertheless, the reliability of SiC power modules has been identified as a major area of uncertainty in applications which require high reliability. Traditional power module packaging methods developed for silicon chips have been adopted for SiC and the different thermomechanical properties cause different fatigue stresses on the solder layer of the chip. In this paper, a 2-D finite element model has been developed to evaluate the stress performance and lifetime of the solder layer for Si devices, which has been validated using accelerated power cycling tests on Si IGBTs. The proposed model was extrapolated for SiC devices of the same voltage and current rating using the same solder material and the results show that under the same cyclic power loss profile the induced stress and strain energy in the die attach layer is much higher and concentrates on the die/solder interfacial area for SiC chips. Using the validated stress-based model, the lifetime can be quantified when SiC chips are used. This ability to extrapolate the available power cycling and lifetime data of silicon chips to SiC chips would be a key element for developing reliable packaging methods for SiC devices.

A 50-kW High-Frequency and High-Efficiency SiC Voltage Source Inverter for More Electric Aircraft

High power density is required for power converter in more electric aircraft due to the strict demands of volume and weight, which makes silicon carbide (SiC) extremely attractive for this application. In this paper, a prototype of 50-kW SiC two-level three-phase voltage source inverter is demonstrated with a gravimetric power density of 26 kW/kg (without inclusion of filter). A gate assisted circuit is introduced to reduce the switching loss. In addition, the ringings of voltage and current due to parasitic parameters during the switching transition can also be mitigated. A mathematical model with consideration of various parasitic parameters is developed, which illustrates the parasitic effects in high-speed switching SiC power module. The converter is operated at a switching frequency up to 100 kHz and a narrow dead band of 250 ns. The measured efficiency is 97.91%.

(Invited) Requirements for Highly Accurate Multiphysics Modeling of SiC Power MOSFETs and Power Modules

With the current needs towards achieving significantly higher power density and energy efficiency of power conversion, the industry is highly interested in replacing mature Silicon devices with the emerging Silicon Carbide (SiC)-based technology in the new generation of power electronics systems. Multi-physics modelling represents a very important design step used to evaluate and confirm the potential of SiC devices in a wide-range of power electronics applications before any prototypes are constructed. It enables a detailed assessment of SiC technology with respect to different performance aspects including dynamics, thermal capabilities, and robustness against abnormal operating conditions. As a prototypical example, this paper presents a highly accurate modelling procedure for analyzing short-circuit (SC) capabilities of a commercial SiC power MOSFET (80mΩ, 1.2kV). First, the actual MOSFET structure is modeled in Synopsys Sentaurus TCAD tool suite and calibrated to match the I-V and C-V MOSFET characteristics, taking into account the mobility degrading effects and interface states at the SiC/SiO2 interface. In the next step, TCAD mix-mode simulations are performed using the developed physical model to gain a better understanding of the design parameters like cell pitch, channel length and p-base doping concentration and their impact on the MOSFET SC and dynamic characteristics considering temperature dependencies and design constraints. Accordingly, a trade-off analysis between improved SC capabilities and a good MOSFET dynamic performance will be discussed, which can be further used as a guideline for developing an optimized MOSFET structure. Moreover, a detailed three-dimensional electromagnetic model of the SC measurement setup will be presented in order to identify the influence of the circuit parameters on the current profile of the Device-Under-Test (DUT) during the SC events and to optimize the measurement setup. For a comparison between the measured and simulated MOSFET waveforms, coupling of electrical and electromagnetic domains will be performed in LTSpice, Saber and TCAD mix-mode tool. As a result, this paper will demonstrate the accuracy of three device models side-by-side: the compact device model implemented in LTSpice, the behavioral model of Saber, and the TCAD numerical model. Finally, the paper emphasizes the requirements for a very accurate and efficient multi-domain modelling procedure that can be integrated in the overall development process of SiC power MOSFETs. Fig. 1 A comprehensive analysis of short-circuit (SC) capabilities of a commercial SiC power MOSFET (80mΩ, 1.2kV) based on a multi-physics modelling approach. Figure 1

A Review of SiC Power Module Packaging: Layout, Material System and Integration

Silicon-Carbide (SiC) devices with superior performance over traditional silicon power devices have become the prime candidates for future high-performance power electronics energy conversion. Traditional device packaging becomes a limiting factor in fully realizing the benefits offered by SiC power devices, and thus, improved and advanced packaging structures are required to bridge the gap between SiC devices and their applications. This paper provides a review of the state-of-art advanced module packaging technologies for SiC devices with the focuses on module layout, packaging material system, and module integration trend, and links these packaging advancements to their impacts on the SiC device performances. Through this review, the paper discusses main challenges and potential solutions for SiC modules, which is critical for future SiC applications.

(Invited) Requirements for Highly Accurate Multiphysics Modeling of SiC Power MOSFETs and Power Modules

Highly accurate modeling of Silicon Carbide (SiC) Power MOSFTEs and their packages represents the basis for virtual prototyping of emerging SiC power devices. The main aim of virtual prototyping is to gain a comprehensive physical understanding of the electro-thermal behavior of SiC power MOSFETs and as well as of the influence of parasitic inductive, capacitive and resistive elements of power modules on the actual dynamic performance of SiC devices without any hardware prototyping. A modeling approach based on linking the results from state-of-the-art commercial multi-domain tools to circuit simulators is presented demonstrating the challenges of developing accurate and fast multi-physics modeling environments, which will enable virtual prototyping of advanced all-SiC power electronics systems with optimized performance.