Michael Meisser

Copper thick-film substrates for power electronic applications

Substrates for high power electronic systems are dominated by DCB-technology. Recently, new copper thick-film pastes have been proposed for use as high power substrates. They are compatible with Al2O3- and pre-oxised AlN-substrates. This paper investigates production processes to build up highly reliable power modules and explores basis electrical and thermal properties of thick-film copper substrates. Fired copper film thicknesses of 300 μm have been produced by subsequent print-dry-fire cycles. Smooth surfaces and copper films with a density of about 70 % of bulk copper have been produced. A power module comprising of 650 V IGBTs, diodes and an intelligent hall sensor with copper traces and spaces of 200 μm is presented. Wire bonding processes on copper thick-films with 500 μm aluminium wire and 400 μm copper wire are discussed. Test units with a 1200 V IGBT were built up. The IGBT was attached at 250 °C and a pressure of 15 MPa using a novel silver sinter paste. This paste can be directly used on copper. The current-carrying capacity of the thick-film test samples was found to be reduced by 10% in comparison to the DCB test device. No significant difference was found in the performance of both technologies in active power pulse tests lasting a few seconds. The number of cycles for test devices with sintered chips, bonded with 400 μm copper wire bonds exceeded 450,000 cycles in a cycles from 25 °C up to 150 °C.

Highly integrated power modules based on copper thick-film-on-DCB for high frequency operation of SiC semiconductors — Design and manufacture

This paper encompasses the design and the manufacture of a full-SiC module based on copper thick-film. Both DC-link capacitors as well as gate drives are implemented onto the substrate in order to minimise parasitic inductances. Thus, the module is especially suitable for high-frequency operation such as inductive energy transfer and inverter systems for renewable energies and electrical vehicles. In order to maintain high mechanical strength of the modules substrate, a Direct Copper Bond (DCB) provides the basis for multiple thick-film layers. The used thick-film dielectric insulates the gate-drive islands and also works as solder-stop material. The heat-spreading capabilities of DCB substrates are investigated by simulations.

Switching speed-control of an optimized capacitor-clamped normally-on Silicon Carbide JFET cascode

This paper presents the results of controlling the switching speed (dv/dt) of an optimized version of the capacitor-clamped normally-on Silicon Carbide (SiC) JFET cascode. The cascode circuit is an easy way to employ the normally-on SiC JFET in a normally-off configuration using a low-voltage Silicon (Si) MOSFET in series connection. The traditional cascode circuit exhibits some disadvantages, namely limited control of the switching speed and high frequency oscillations on the drain-source-voltage of the low-voltage Si MOSFET. The optimized capacitor-clamped cascode reduces the oscillations and enables control of the voltage and current slopes as well as implements a protection of the JFET gate. The theoretical background of the capacitor-clamped cascode and the control of voltage slope are explained and investigated experimentally.

Universal resonant topology for high frequency pulsed operation of Dielectric Barrier Discharge light sources

This paper reports about emerging techniques for the efficient drive of Dielectric Barrier Discharge (DBD) plasma light sources in pulsed operation mode. Besides a classification of pulse topologies, the novel Universal Sinusoidal Pulse topology, that provides high voltage amplification and high frequency operation, is presented. Transformer equipped and transformerless variations of the topology are presented. Experiments prove electrical efficiencies of more than 80%, while power measurements are cross-checked by thermal measurements. Additionally, frequency domain characteristics of the used DBD-lamp were analyzed and magnetic storage devices with distributed center gap are presented.

Connector-less SiC power modules with integrated shunt - low-profile design for low inductance and low cost

This paper presents the design, manufacture and characterization of connector-less 1200 V SiC MOSFET half-bridge power modules based on AlN DCB substrate. The modules contain four MOSFETs and no external antiparallel diodes. They are rated for a current of 40 A and include a shunt. Static and dynamic measurement results are presented. Multiphysics simulations are used to validate the measured data. The modules show a power path inductance below 3 nH. The power rating of the implemented chip shunt resistors is sufficient for the performed characterizations but requires revision. The switching loss at turn-on is 340 μJ at 23 A, 800 V, the turn-off loss is well below 50 μJ, principally allowing MHz operation in resonant mode.

Low-temperature silver sintering processes on high performance ENIG, EPIG, ENEPIG and ISIG surfaces for power electronic systems and huge battery systems

Low-temperature low-pressure silver sintering is a die attachment process for highly reliable power modules. The quality of the sintered interconnection strongly depends on the properties of substrate metal, the die metallization and the sinter paste. This paper investigates the properties of chips sintered at 10 MPa and 250 °C on recently proposed gold layers, which are electrochemically deposited on nickel, palladium and silver layers in a mixed displacement and autocatalytic reaction. This specific deposition process leads to ENIG, EPIG ENEPIG and ISIG finishes comprising a gold layer of high purity, which was proven utilizing X-ray Photoelectron Spectroscopy (XPS) and FIB-SEM sections. Shear tests demonstrated the high quality of the sintered interconnection. Shear values at room temperature exceeded 80 N/mm2. After storing the substrate for two hours at 200 °C or for one hour at 350 °C prior to the sintering process shear values over 80 N/mm2 were measured. Gold layers deposited by this new process are very suitable for silver sintering processes and tolerant to various sinter pastes from different manufactures. Shear values derived from a paste of a different vendor exceeded 180 N/mm2, resulting in copper torn out of the DCB.