Integration, higher switching frequency, and increased efficiency demands for SiC MOSFET devices are placing stricter requirements on power module packaging formats and processes. This article outlines evolution trends in SiC module packaging across interconnects, sintering technologies, and materials.
1. Interconnect and sintering technologies
Internal interconnect methods are shifting from aluminum wire bonding and ultrasonic welding to copper wire bonding. Chip-to-substrate joining is moving from traditional Pb/Sn solder to silver sintering.
Silver sintering offers excellent electrical and thermal conductivity, high bond strength, and strong stability. Nano-silver sintered modules can operate long-term at elevated temperatures. The sintered layer forms reliable mechanical and electrical connections, reducing module thermal resistance and internal resistance, thereby improving performance and reliability. Silver sintering can increase module lifetime by approximately 5 to 10 times. The sintered layer thickness is about 60 to 70 percent thinner than solder layers, and thermal conductivity can be increased by roughly three times.
Silver sintering has become one of the most widely applied processes in third-generation semiconductor packaging worldwide. Many suppliers have adopted silver sintering as a core technology and developed double-sided silver sintering. Approaches include sintering silver foil on the chip front to replace aluminum wire bonding or eliminating the baseplate and sintering the substrate directly to the heatsink, which simplifies module structure. The technology has progressed from micron-scale silver sintering to nano-silver sintering. Compared with micron-scale processes, nano-silver sintering significantly reduces required bonding temperature and auxiliary pressure, greatly expanding the usable process window.
The SiC single device in the Model 3 is bonded to the heatsink using silver sintering. In 2006 Infineon introduced the EasyPACK 1 package, which used single-sided and double-sided silver sintering. In 2015, Mitsubishi Electric used silver sintering to produce power modules with cycle life about five times that of soft solder.
In the Chinese market, Sida Semiconductor's T6 series automotive-grade discrete devices for 1200 V and 750 V will adopt silver sintering; dual-sided cooled N3 and N7 series are also expected to offer SiC versions by late 2022, using double-sided silver sintering. Other SiC module vendors such as Xinjuneng and Lips are also actively developing silver-sintered packaging processes.
As silver sintering process costs decline, demand for silver sintering materials and equipment will increase. Boschman Technology assisted Tesla with early assembly of SiC modules, handling sintering, welding, wire bonding, molding, trimming, and finishing. In April 2022, Boschman was acquired by Suzhou Boschman Semiconductor Equipment Co., Ltd., which plans to establish a facility in Suzhou.
ASMPT Pacific Technology Co., Ltd. is a major supplier of advanced semiconductor packaging equipment and microelectronic packaging solutions. Its SilverSAM sintering equipment incorporates patented anti-oxidation and uniform pressure control technologies. In addition to ensuring high-strength sintered bonds that meet thermal and electrical conductivity requirements, the system supports higher IPM chip density designs and, together with future copper sintering bonding directions, helps SiC modules realize high-power performance.
Domestic equipment suppliers have begun to offer partial replacements in this segment. In 2021, Shenzhen Advanced Connection Technology Co., Ltd. won a procurement project for sintering equipment from BYD Semiconductor with its AS (Ag-Sintering) series sintering systems. Other equipment companies such as Jiayuan Haoze and Tuoding Electronics are also developing related solutions.
2. Materials
Substrates are upgrading from alumina to silicon nitride, aluminum nitride, and AMB thick-copper substrates, and molding encapsulation is replacing traditional potting. Traditional HPD commonly uses alumina, which is inexpensive and readily available but has limited heat dissipation. New substrate materials include silicon nitride, aluminum nitride, and AMB thick-copper substrates. Aluminum nitride is generally used in industrial applications, silicon nitride is commonly used in automotive applications, and AMB thick-copper substrates are used in onboard SiC applications.
Substrate selection is critical for module thermal design. The mainstream power semiconductor module packaging still uses DBC (direct-bond copper) ceramic substrates. AMB thick-copper substrates offer thermal conductivity roughly three times that of DBC alumina and provide better mechanical strength and performance. As SiC power modules mature, AMB is expected to become a growing trend in electronic module packaging. In addition, molded modules have advantages over hybridpack modules, including lower stray inductance and higher reliability.
