Environmental policies and stronger consumer preferences in the deployment of energy in for example, industrial, automotive and transportation applications means that products and equipment must meet new levels of efficiency, service life and compactness. Power electronics is a key technology to assure future mobility with electric and hybrid vehicles, the answer to increasing emissions and limited natural resources. Manufacturers are developing new assembly and connection technology, offering higher current densities and reliable chip temperatures, as well as using new semiconductor materials.
By Thomas Grasshoff, Head of Product Management,
Profitable to the power semiconductor industry
The power semiconductor industry will profit from the forthcoming growth in the HEV and renewable energies market in two respects. Firstly, power semiconductors are needed for energy conversion itself – for instance in inverters in wind power plants. Secondly, semiconductors are the core element of variable speed drives.
Owing to their technical superiority as well as for reasons of user-friendliness, modules are used predominantly as electronic switches. A module comprises a silicon chip, an insulated ceramic substrate and a module case, housing the necessary power connections. For the designer, there are many issues to consider regarding assembly and connection technology, as well as the integration stage, for example including integrated driver, current sensor and heat sink.
In the world of industrial drives, HEVs and renewable energy generation, reliability is top priority simply because this is what maximises economic operation. In addition, high efficiency and compactness of the system are essential for customers. For manufacturers of power semiconductors, this translates to a particularly difficult challenge in meeting these, in some respects, conflicting requirements. Furthermore, as inverter power increases, parallel module connection and heat management become increasingly important.
New challenges for power module manufacturers
In a conventional soldered power module with a base plate, the solder connections often constitute one of the weak points of the module. The base plates themselves, for modules with large dimensions and consequently high power output, can only be optimised with some difficulty in view of best thermal and mechanical performance. For modules of 200A and above, several semiconductor chips have to be connected to the DCB (Direct Copper Bonding) ceramic in parallel in order to achieve modules with increased current ratings. Chip temperatures have to be carefully considered in the light of reliability and here, the significant improvements in semiconductor technology now allow for higher operation temperatures.
Innovative technologies provide solutions
These problems are all interdependent factors. It therefore makes sense to search for an integral solution rather than looking at the problems as isolated matters.
The challenge faced by the designer concerning the base plate and solder connections can be resolved, for example, with Semikron’s SKiiP technology, where the base plate and large, fatigue-prone solder connection to the substrate are removed entirely. A patent-protected pressure contact system is used instead. In the pressure contact system, the substrate is pressed onto the heat sink by way of mechanical pressure. As the ceramic substrate is relatively flexible and the pressure applied by way of mechanical “fingers” located at several points, very close contact between the ceramic substrate and the heat sink is reliably achieved. As a result, the thermal paste layer can be reduced to a minimum of just 20-30μm. By way of comparison, the thermal paste layer in conventional modules with base plates is in the order of 100μm.
But despite the current economic situation, the drives and renewable energy sectors will continue to play a vital role in boosting industrial production and employment rates for the future. The power semiconductor industry has already taken on the challenges ahead. The technological demands posed by hybrid and electric vehicles, as well as new materials such as SiC and GaN will certainly pave the way for new developments.
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