Mass commercialization of SiC technology is driven by EV/HEV, renewable energy, and rail applications.
Silicon Carbide as a new type of semiconductor material has wider band-gap compared to Si, and SiC MOSFET has much shorter turn on and off time, no tail current compared to IGBT, therefore allows for higher switching frequencies compared to regular silicon devices.
At the same time, it can be operated at higher temperatures and at higher voltages compared to traditional Si semiconductors.
Power Electronic Substrate
Direct bonded copper (DBC) and Active Metal Brazing (AMB) substrates are commonly used in power modules. They are composed of a ceramic tile with a sheet of copper or aluminum bonded to one or both sides by a high-temperature oxidation process
The role of the substrate in power electronics is to provide the interconnections to form an electric circuit, and to cool the components. These substrates must carry high currents and provide a high voltage isolation. They also must operate over a wide temperature range (up to 300°C).
Sintering is a solid state material transport process based on atomic diffusion.
The starting materials are nano- and micro-sized Ag or Cu particles possessing high surface energy.
- Green. Lead free
- High remelting temperature
- Excellent thermal and electrical properties
- Reliability. Higher reliability at harsh conditions
Ultrasonic Welding of Power Terminals
Traditionally soldering is the technology of choice for connection electrode terminals in high power packages. However, degradation of the solder due to CTE mismatch of copper and solder layer will very likely lead to fail under thermal cycling. So advanced joining and interconnection technologies have to solve reliability challenges.
Ultrasonic welding is an industrial process whereby high-frequency ultrasonic acoustic vibrations are locally applied to workpieces being held in close contact under pressure to create a solid-state weld.
Ultrasonic welding is well-received for joining power terminals to the electric circuit of DBC and AMB substrates. Direct ultrasonic welding between copper terminals and the top metal layer of DBC/AMB-substrates provides high reliability because the bonding area has uniform CTE.
Advantages of Ultrasonic Welding:
- High reliability and improved power cycling capability due to no intermetallic phase / no CTE difference
- Higher maximum load current compare to wire bonding
- Less power loss, higher electrical efficiency, minimizing cooling requirement
- Short process time without involving heating the module
- Comparable low energy and low-cost process
Heavy Copper Wire Bonding
Ultrasonic wire bonding is extensively used in microelectronics packaging to make interconnections between the die and the package metallization. It is a solid-state welding process in which a copper or aluminum wire is welded to a metallized surface using a combination of US energy and normal force. Heavy wedge-wedge bonding wire (diameters in the range of 100–500 µm) is widely used in power modules and other high-power applications.
The recent interest in employing copper wire for interconnections instead of aluminum wire in power module packaging is driven by a number of superiorities.
Advantages of heavy Cu wire bonding compare to Al wires:
- Lower resistivity
- Higher thermal conductivity
- Lower CTE mismatch with substrate and die
- Higher yield strength and mechanical stability
- High thermo-mechanical reliability under harsh conditions
However, heavy copper wire bonding has its limitations. Due to copper hardness high ultrasonic power and high bonding force are required, that might damage bond pad. Furthermore, copper naturally tend to oxidize, which lead to not sufficient bonding and require more difficult complex bonding set-up.
Heavy copper wire bonding is an advanced skilled process. Semiland has engineer team with right technical background and experience to get the job done.