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Semikron - New packaging technology replaces wire bonding

17th May 2011

Semikron Ltd

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Semikron has developed a revolutionary packaging technology for power semiconductors, which removes the need for bond wires, solders and thermal paste. The new SKiN technology is based on the use of a flexible foil and sintered connections. Current density is doubled to 3 A/cm2 compared with the 1.5 A/ cm2 achievable with standard wire bond technology. Converter volume can therefore be reduced by 35%. This reliable and space-saving technology is the optimum solution for vehicle and wind power applications.

This results in a higher current-carrying capacity and ten times the load cycle capability – unthinkable with the wire bonding used in power electronics in the past. Wire bonding has been the main method of connecting the chip top-side connection to a direct-bonded copper (DBC) substrate for the past 25 years. Wire bonding cannot meet the need for higher current densities that has resulted from recent technical advances, meaning that reliability is impaired. In the new packaging, a sintered foil replaces the wire bonding on the chips and the underside of the chip is sintered to the DBC. This results in optimum thermal and electrical chip connection, since sintered layers have a lower thermal resistance than solder equivalents. The sintered foil connects the chip across its entire surface, whereas bond wires connect the chips at the contact points only. Thanks to the high load-cycle capability offered by this new packaging technology, higher operating temperatures are possible. The move towards new materials, such as SiC and GaN, will increase the need for these elevated temperatures.

In addition to removing the need for wire bonding, the new packaging solution is free of solder thermal paste. Instead, a sinter layer replaces the thermal paste layer and the soldered base plate. Thermal paste is responsible for around 30% of the total thermal resistance in a system. By replacing this, the thermal conductivity between chip and heat sink is improved, resulting in a 30% increase in usable electric current.

SKiN Technology enables a 3 MW wind power converter to be fitted into a single switch cabinet. A 90 kW converter for hybrid and electric vehicles can be 35% smaller than the smallest converter on the market today. For converters in vehicles and wind power units, liquid-cooled systems are used, and the compact and lightweight converters used offer Semikron’s customers an important competitive edge with their reduced thermal impedance and increased power-cycle capability.