Development of Embedded High Power Electronics Modules for Automotive Applications

The automotive industry has a strong demand for highly reliable and cost-efficient electronics. Especially the upcoming generations of hybrid cars and fully electrical vehicles need compact and efficient 400 V power modules. Within the engine compartment installation space is of major concern. Therefore small size and high integration level of the modules are needed. Conventionally IGBTs and diodes are soldered to DCB (Direct Copper Bond) ceramics substrates and their top contacts are connected by heavy Al wire bonds. These ceramic modules are vacuum soldered to water-cooled base plates. Embedding of power switches, and controller into compact modules using PCB (Printed Circuit Board) technologies offers the potential to further improve the thermal management by double-sided cooling and to reduce the thickness of the module. In the recently started “HI-LEVEL” (Integration of Power Electronics in in High Current PCBs for Electric Vehicle Application) project, partners from automotive, automotive supplier, material supplier, PCB manufacturer and research teamed up to develop the technology, components and materials to realize high power modules. The following topics of the development will be addressed in detail in this paper:Assemble of power dies (IGBT and diode) using new sinter die attach materials:The deployment of new no pressure, low temperature sinter paste for the assembly of the power dies is a mayor development goal. Here the development of a reliable process to realize a defect free bonding of large IGBT dies (up to 10x14mm2) is essentially. These pastes are applied by stencil printing or dispensing and the sintering will take place after die placement at temperatures of around 200 °C.Thick copper substrate technology:To handle the high switching current, suitable copper tracks in the PCB are required. The realization of such thick copper lines (up to 1mm thickness) requires advanced processing, compared to conventional multilayer PCB production. In this paper the essential development steps towards a 10 kW inverter module with embedded components will be described. The process steps and reliability investigations of the different interconnect levels will be described in detail.

Cofiring behavior of multilayer inductors based on substituted Y- and M-type hexagonal ferrites

Sinter-active soft ferrites with adequate permeability profiles are required for the fabrication of multilayer ferrite inductors (MLFI). For MLFI fabrication, a Low Temperature Ceramic Co-firing (LTCC) process is used. Substituted hexagonal ferrites of Y-, and M-type represent an important family of soft ferrites which might operate at high-frequency conditions up to 2 GHz. However, for Ag-based multilayer inductor applications a sinter process at 900°C is required. Low-temperature sinter-ability is provided by the use of sub-micron powders and/or sintering additives. Substituted Y-type hexagonal ferrites Ba2Co2-x-yZnxCuyFe12O22 were obtained after sintering at 1000°C. Substitution of Cu for Co improved the low-temperature sintering behavior. The addition of 5wt.% Bi2O3 guarantees almost complete densification at 900°C. The saturation magnetization and permeability are significantly affected by the Zn-concentration. A maximum permeability of μ′ = 10 and cut-off frequency fg~2GHz was observed for a ferrite with y = 0.4. Co/Ti-substituted M-type BaFe12-2yCoyTiyO19 ferrites can also be used for multilayer inductors. The magneto-crystalline anisotropy changes from uniaxial to planar upon Co/Ti-substitution, and ferrites with y≥1.1 exhibit soft magnetic behavior. Ferrite powders were prepared at 1000°C. The addition of a sintering aid shifts the temperature of maximum shrinkage down to below 900°C and dense samples were obtained after firing at 900°C. A permeability of μ′ = 16 and a resonance frequency of 1 GHz was observed. Substituted M-type ferrites are stable during co-firing at 900°C and show no sign of decomposition, i.e. these materials are LTCC-compatible. Ferrite tapes were prepared by tape casting and multilayer structures were fabricated by screen printing, stacking, lamination and final co-firing. Firing was performed at LTCC conditions i.e. 900°C. We report on the co-firing behavior, microstructure and permeability of monolithic laminates. It is shown, that hexagonal Co2/Zn2Y- and Co/Ti-M-type ferrites are excellent magnetic materials for multilayer inductors.

Modeling Cooling Process of High Temperature Sinter

In the paper, a 1-D unsteady mathematical model for the Gas-Solid heat transfer process of high temperature sinter has been developed, and is used to analyse the cooling process of high temperature sinter. A set of measured data is used to verify the modeling result. The agreement between the measured and the modeling is good. The effect of operation parameters on the cooling process of the annular cooler has been investigated.