What will be the SiC device packaging solutions? Who are the first adopters?
Where in EV/HEV systems is the highest market potential for SiC?
According to Yole Développement (Yole) and System Plus Consulting‘s analysts, governmental targets for the reduction of CO2 emissions are the main drivers for the electrification of passenger vehicles. Currently, car makers focus on vehicle electrification as a very effective way to reduce their vehicle fleet CO2 emissions and in such a way to avoid heavy financial penalties. Vehicle models with different electrification levels have been introduced to the market, ranging from mild-hybrid electric vehicles (MHEVs), full hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs) to zero-emission Battery Electric Vehicles (BEVs) and Fuel-Cell Electric Vehicle (FCEVs).
In the past, it was expected that the transition to full electric vehicles would remain rather slow and incremental. This was mainly due to the high battery cost and short driving range of electric vehicles. Due to the rapidly improving battery technologies, decreasing battery manufacturing cost, supply chain consolidation and many other factors, an accelerated deployment of electric vehicles is being observed.
In the Power Electronics for E-Mobility 2021, Yole’s analysts assert that electric and hybrid electric vehicles (EV/HEV) have become the key driver for power electronic industry innovations, with a strong focus on traction inverters for battery electric vehicles. The EV/HEV market will surpass 41 million vehicles in 2026 and will experience a CAGR2020-2026 (Compound Annual Growth Rate) of 35%.
Why specifically battery electric vehicles? Battery electric vehicles are already a relatively big and rapidly growing market, and BEVs are considered as an ultimate end-point of vehicle electrification, thus representing a sustainable business opportunity. Why traction inverters? The traction inverter, together with the battery and electric motor, are the three key differentiation elements when comparing technology performance of vehicles from different suppliers. Increased inverter efficiency results in lower energy losses on the way from the battery to the motor and enables a longer driving range. The inverter characteristics also have a direct impact on the vehicle performance and user driving experience.
Car makers are becoming increasingly intrusive in the design and manufacture of power modules. As power module packaging is a relatively new concept for car makers, it takes time to develop a power module with high performance and low manufacturing costs. Some car makers thus prefer to focus directly on newer silicon carbide (SiC) MOSFET technology, instead of facing competition from power module makers with strong experience in already well-established silicon IGBT automotive power modules. This focus on SiC power module development has been strengthened by the adoption of SiC modules in traction inverters in Tesla Model 3 vehicles.
Security of supply as one of the key success factors for SiC technology adoption
Indeed, the 2017-2019 period was remarkable for the SiC market following the Original Equipment Manufacturer (OEM)’s adoption of SiC in the Model 3, which was then extended to the Model S and Model X. Not only has Tesla demonstrated the full performance benefit of SiC in the traction inverter, but it also reduced the chasm between the silicon and wide band gap worlds. Since then, the development of automotive qualified SiC devices has accelerated, the design wins for main inverter and on-board chargers multiplied, and new models having SiC inside hit the road. Indeed, in 2020 Chinese OEM BYD launched its HanEV model while US-based Lucid introduced Lucid Air, both equipped with main inverters using full SiC modules. SiC has just started its penetration into the emerging EV/HEV business and many other exciting adoption stories are sure to arrive. According to Yole Développement’s (Yole) Compound Semiconductor Monitor Q3-2020 Update, power SiC devices in EV/HEV is poised to grow beyond US$1.5 Billion in 2025 by posting a CAGR2019-2025 of 29%.
Following the successful adoption of SiC devices, one of the most important questions raised in the industry has been “Will there be a sufficient supply of SiC wafers?”. To meet the growing demands, leading substrate players, such as Cree, SiCrystal (ROHM company), II-VI, have made significant investment in crystal growth, while almost all leading device manufacturers have acquired or have accelerated the internal growth of wafering technology. During 2019-2020, the leading SiC device manufacturers STMicroelectronics, Infineon and ON Semiconductor signed long-term agreements with leading wafer and SiC crystal suppliers such as Cree, SiCrystal and GTAT.
Since the arrival of 800V battery electric vehicles, 1200V SiC has indeed become more of interest. In development for several years now, 1.2kV SiC MOSFET technology targeting traction inverter applications has been high on the priority list of numerous device manufacturers. The next priority is to develop suitable packaging in order to fully benefit from the added value of SiC MOSFETs.
“Do SiC modules need new and innovative packaging solutions?” In order to better address this question, it is first important to understand the current market and technology trends identified by Yole and System Plus Consulting. In electric vehicles, the available space in the engine compartment is often limited. Therefore, the electric power train in the EV needs to be much smaller, requiring a higher power density. Consequently, new packages are needed to improve device performance. In fact, at higher temperatures the standard plastic case packages could have problems of reliability at different levels, from wire bonding and substrate to encapsulation. Moreover, to remain competitive in a contested market, the power module makers must strike a balance between high levels of reliability and remaining cost efficient.
As electric vehicle is still a relatively new business segment, many players focus on product differentiation by concentrating on high performance. This is often achieved by using very specific and proprietary module designs based on packaging solutions enabling high performance and high reliability.The traditional power modules with a plastic case, all wire bonding, and Tin-based solder are still offered by manufacturers, but new solutions allow better integration of the module into the final system according to the performance requirements. Manufacturers have been developing different solutions, such as limiting wire bonding or using over molded structures to efficiently cool the power semiconductor chips, to reduce electrical interconnection inductance, to improve the reliability.
Various trends at different levels can be found in the actual packaging landscape:
Packaging aspect (transfer molded structure, plastic case, metallic case…), baseplate design (pin fin…), baseplate assembly (external baseplate, integrated baseplate in metallic case…), cooling technology (single or double side cooling), substrate (SiN AMB…), die attach (silver sintering, screen-printing Tin-based attach…) and die substrate (SiC, Si).
Molded double-side cooling modules eliminate the need for a plastic case and enable more compact and highly modular inverters. This is the case for Hitachi Double Side Cooling Power Module with its integrated baseplate in metallic case, as analyzed in System Plus Consulting’s Hitachi Double-Side Cooling Power Module from Audi E-tron’s Inverter report.
Similarly, Infineon Technologies and Toyota propose their own solution for double-side cooling. The modules are different not only because of the different number of switches but also because of the different materials. Differences in the lead frames, the spacers and the die attach material are observed. Furthermore, substrates have a big impact on thermal dissipation; copper has seen widespread use as a material for lead frames while new integrated heatsinks with pin-fin, AMB (Active Metal Braze) ceramic substrates are increasingly being used.In addition, solder plays a role in increasing module reliability especially at higher temperatures. The use of silver sintering is becoming more and more common and can be found at different levels, either under the die or under the substrate.
To reduce inductance caused by connections, a trend toward copper clips or bigger connections rather than thick wire bonding has been observed. As mentioned in System Plus Consulting’s Mitsubishi J1- Series 650V High-Power Modules for Automotive Report, instead of the classical silicone gel, Mitsubishi uses new epoxy resin.
New semiconductor technology needs new adapted power module packaging solutions.
Thus, to fully benefit from SiC technology advantages, new power module packaging solutions must be developed, since SiC devices can work at higher junction temperatures and higher switching frequencies with smaller die sizes. Power module packaging solutions are moving toward high-performance materials and a reduction in the number of layers, size, and interfaces, while conserving electrical, thermal, and mechanical characteristics.
A “golden triangle” is often considered for the highest performance and reliability of SiC power modules for EV traction inverters: SiC die, silver sintering die attach and Silicon Nitride (SiN) AMB ceramic substrate. This is the case for STMicroelectronics SiC Module in Tesla Model 3 Inverter as analyzed in System Plus Consulting’s Tesla Model 3 Inverter report.
Thanks to its collaboration with STMicroelectronics, Tesla’s inverter is composed of 24 1-in-1 power modules assembled on a pin-fin heatsink. The module’s SiC MOSFETs are sintered on SiN AMB and connected directly to the terminals with copper clips and thermally dissipated by a pin-fin baseplate.
However, the solution with the highest performance is not always the one chosen by the customer – manufacturing cost is also an important factor of choice. While the choice of power module material and its design are fundamental for device performance, the “design for manufacturing” is crucial to reduce the costs.
The rapid evolution of technology on all design levels and the cost of modules are the two factors that in recent years play against the standardization in power module design, and we expect even more innovative designs and packaging solutions in the future. The requirement for cost saving during the integration steps drives companies to develop innovative packaging and module integration solutions. As a direct consequence, the power module packaging supply chain is expected to undergo significant changes.
After an initial focus on high performance and high reliability, one can expect that the development focus will move to cost reduction. This is needed to better compete with existing power module solutions based on silicon IGBTs. One can now confidently state that SiC will always be in direct competition with low cost and mature Silicon, which is itself a moving target. Nevertheless, the system benefits are plentiful. That is why the beginning of a remarkable SiC era in the power electronics business is being witnessed!
This article was written for EMOBILITY TEC.
About the authors
As a Technology & Market Analyst, Compound Semiconductors, Ezgi Dogmus, PhD, is member of the Power & Wireless division at Yole Développement (Yole). She contributes daily to the development of the activities of the division with a dedicated collection of market & technology reports as well as custom consulting projects. Prior to Yole, Ezgi was deeply involved in the development of GaN-based solutions at IEMN (Lille, France). Ezgi also participated in numerous international conferences and has authored or co-authored more than 12 papers. Upon graduating from University of Augsburg (Germany) and Grenoble Institute of Technology (France), Ezgi received her PhD in Microelectronics at IEMN (France).
Milan Rosina, PhD, is Principal Analyst, Power Electronics and Batteries, at Yole Développement (Yole), within the Power & Wireless division. He is engaged in the development of the market, technology and strategic analyses dedicated to innovative materials, devices and systems. His main areas of interest are EV/HEV, renewable energy, power electronic packaging and batteries.
Milan has 20 years of scientific, industrial and managerial experience involving equipment and process development, due diligence, technology and market surveys in the fields of renewable energies, EV/HEV, energy storage, batteries, power electronics, thermal management, and innovative materials and devices.
He received his PhD degree from Grenoble Institute of Technology (Grenoble INP) in France.
Milan Rosina previously worked for the Institute of Electrical Engineering in Slovakia, Centrotherm in Germany, Fraunhofer IWS in Germany, CEA LETI in France, and utility company ENGIE in France.
Ana Villamor, PhD serves as a Technology & Market Analyst, Power Electronics & Compound Semiconductors within the Power & Wireless division at Yole Développement (Yole). She is involved in many custom studies and reports focused on emerging power electronics technologies at Yole Développement, including device technology and reliability analysis (MOSFET, IGBT, HEMT, etc). In addition, Ana is leading the quarterly power management market updates released in 2017.
She holds an Electronics Engineering degree completed by a Master and PhD. in micro and nano electronics from Universitat Autonoma de Barcelona (SP).
Amine Allouche serves as a Technology & Cost Analyst, Power Electronics, at System Plus Consulting, part of Yole Développement.
With strong expertise in the field of power electronics, Amine produces reverse engineering & costing analyses while also working on custom projects. He collaborates closely with the laboratory team, and together they define the objectives of the analyses and determine the methodologies necessary to reveal the structure of a device and all materials required for its development and production. Amine’s aim is to determine the technology choices made by the leading companies.
In addition, Amine runs a daily technology watch to identify innovative power electronics components and related manufacturing processes. His objective is to gain a comprehensive understanding of the evolution of power electronics technologies and to identify the technological strategies of the leading players in this field.
Amine attends numerous international trade shows & conferences where he meets the power electronics companies and discovers the latest innovations. He also presents key results of his studies during webcasts.
Amine holds a master’s degree in Micro & Nanotechnologies with a focus on integrated systems from Grenoble’s Polytechnic Institute (France). He also graduated from the Ecole Polytechnique Fédérale de Lausanne (EPFL) (Lausanne, Switzerland) and the Politecnico di Torino (Italy).
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