The Author wants to convey his enthusiasm and fascination towards power electronics to young talents and to give the “old hands” interesting insights into current developments.
Thomas Stockmeier
Using the example of some technical developments by the hidden champion Semikron, one of the leading manufacturers of semiconductor components and power electronic systems, I would like to explain the significant contribution of power semiconductors to these “mega themes”.
Example 1: Innovative electric vehicles – power electronic systems for battery vehicles
In electrical vehicles, power electronics must be compact, lightweight and function reliably even in harsh conditions. To meet these requirements, Semikron left the conventional technological path a long time ago and began to integrate mechanically all of the functions of the power electronic system. Figure 1 shows the latest Semikron system for forklift trucks in which everything from the power semiconductor chips to the microelectronic components are integrated in a single compact case.
Figure 1. Power electronics for hybrid and electric vehicles for use in the agricultural industry, construction industry, materials handling and all kind of battery-powered vehicles
The development challenge faced is how to incorporate the conflicting electric, mechanical and thermal requirements at no compromise to reliability and at reasonable cost into a design that enables rational production of large volume numbers. The 5.7 liter inverter has a peak current of 400 Aeff for a battery voltage of 160 V and is suitable for direct mounting on the vehicle drive axle. At this mounting position, system function must be guaranteed under 12 g vibrations and mechanical shock of up to 100 g; further, this must be guaranteed for a total lifetime of 20,000 operating hours and ambient temperatures of between – 40 and +85 °C.
A development such as this is only possible, if expertise and know-how in the areas of mechanical engineering, electrical engineering, electronics and thermal engineering are pooled within an interdisciplinary project team. This means that very high requirements have to be met on all accounts, ranging from semiconductor chips to controller software, as well as the team “spirit”.
Equivalent form factor with 30% higher performance
Today, it is not the on-resistance of the MOSFET, but that of the terminals and interconnects that dominates. It therefore makes perfect sense to replace the bond wiring on the chip by a high-conductivity copper strip. In just a few years this will be deployed to new products. The solder chip-to-substrate connections plus the pressure contact system used to connect the insulating substrate to a heat sink using thermal grease results in considerable thermal resistances. Ongoing developments are focussing on the replacement of these two interfaces with sinter technology developed by Semikron. This new packaging technology helps reduce thermal resistances and enables a far higher number of thermal cycles - in other words chip performance is improved. Likewise, the current sensors and gate driver are being steadily reduced in size, and the power density of the DC link is steadily increased. The resulting product is an inverter that could realistically offer around 30% higher power per volume than the latest state-of-the-art systems.
Example 2: Intelligent power semiconductor modules for WPUs
As much as 20 years ago, for the very first wind power turbines, Semikron developed specific IGBT modules which, thanks to innovative pressure contact technology and the functional integration of power section, gate driver and sensors, were able to meet the high demands in terms of long-term reliability and power density. Today, our SKiiP IPMs are already in their third generation, with more than 60 GW of installed wind power featuring SKiiP technology, figure that equals around half the total wind power generation capacity in place worldwide.
At present, the fourth generation of the SKiiP-IPM (SKiiP4) is in the market launch stage. Figure 2 shows a sixfold SKiiP4 IPM for 3600 A (the performance of a fourfold SKiiP3 – currently in use – is 1800 A both for 1700 V blocking voltage).
Figure 2. The new sixfold SKiiP4-IPM for 3600 A and 1700 V. Every module undergoes a tough burn-in test.
Thanks to SKiiP4 and by utilizing the latest IGBT and diode technology, we have managed to develop an IPM that offers 30% more power at no increase in size. And, in line with the trend towards higher wind power, the total possible output grows by one third. The IGBT and diode chips used in SKiiP4 power modules are not soldered to the substrate but are sintered instead. This increases load cycle capability by a factor of five and reduces thermal resistance by around 10%.
Increased DC link voltages up to 1300 V an be safely controlled by improved gate control, and the requirements for offshore installation and installation at high altitude can be met.
The transition from analogue to fully digital technology for drive, protection, and control means that in future IPM generations, operating logs can be created, service life redictions made, and this and other data can be accessed remotely by serial data protocols. It goes without saying that the new SKiiP4 IPM has to meet the same outstanding performance requirement as its predecessor in terms of an extremly low failure rate. For this reason, every module undergoes a burnin test before being delivered to the customer.
Example 3: MiniSKiiP IPM for industrial drives.
The first MiniSKiiP module was launched around 15 years ago. At that time, this module, which featured spring contacts for the entire power connections, had no base plate and was assembled using a single screw, was revolutionary and enabled the production of smaller and less expensive inverters for variable-speed drives.
Today, MiniSKiiP modules are used in millions of inverters found in variable-speed drives and, thanks to their size and cost reduction benefits, have helped these drives replace more and more uncontrolled drives which are huge energy-wasters.
The next development step was to integrate the gate driver. This resulted in the Mini SKiiP IPM. For this purpose, driver ICs in SOI (Silicon-On-Insulator) technology were developed; one of the main merits of SOI technology is that the IC remains stable and reliable even at today`s maximum IGBT junction temperatures.
For the 1200 V MiniSKiiP IPM, the development of series connected ICs was necessary, since the SOI technology allows for blocking voltages of up to 600 V only. The inputs and outputs of the ICs had to be improved regarding noise immunity, due to their close proximity to the power chips, and the packaging and test technology had to be further developed to accommodate the extended functionality.
The resulting product was the very first IPM with 1200 V IGBT’s for currents of up to 100 A. The customer can still enjoy the benefits of the easy-assembly MiniSKiiP system, but can now also simplify his PCB design considerably since the gate drive function is integrated into the MiniSKiiP.
The next logical stage in MiniSKiiP development is the move away from soldered chip connections to the use of sinter technology. And now thanks to the new SOI IC, which functions reliably up to 200 °C, the combination with SiC chips with their correspondingly higher junction temperatures, is now in reach.
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