Ceramic Embedding Boosts Wide Bandgap Device Performance

April 23, 2019 by Scott McMahan

The use of power electronics in challenging fields of application such as electric vehicles or aerospace implies high-performance requirements of switching speed and reliability. In this context, conventional packaging technologies are frequently pushed to their limits.

Scientists at Fraunhofer IISB have developed a novel packaging concept and technologies that embeds power semiconductor devices into ceramic circuit carriers. Their design offers high-temperature stability, operation at high voltages, and hermetic sealing to deliver a maximum lifetime in harsh environments.

These performance characteristics help to fully exploit the significant advantages of wide-bandgap semiconductors. Fraunhofer IISB will present power modules based on this new approach in May 2019 in Nuremberg.

Ongoing miniaturization, 3D integration, and extreme environmental conditions impose considerable challenges to future power devices, modules, and systems, which are expected to deliver excellent performance, high reliability, and long lifetime.

Low cost is a key, that can be enabled by the ability to operate at high temperature. This ability to operate at high temperatures implies small chip size and low cooling effort.

In this way, the applicability of established packaging technologies, such as those based on PCBs, is limited because they do not afford sufficient thermal stability or current carrying capability.

Fraunhofer IISB in Erlangen, developed one remedy, a novel packaging concept based on the embedding of power semiconductors in ceramic circuit carriers. Fraunhofer IISB asserts that this embedding can be the basis for an extensive and more economical use of wide-bandgap semiconductors such as SiC.

SiC devices offer tremendous potential for the growing market of power electronics. They allow the switching of very high currents and voltages in compact, miniaturized systems, and they are a primary enabler for the development of highly efficient and intelligent solutions for mobility, industrial applications, and energy technology.

With the new approach for packaging and circuit carriers, the existing physical constraints, such as limited operating temperature or undesired parasitic inductances, can be enhanced.

With the new technology that Fraunhofer IISB calls ceramic embedding, the power devices are placed inside a special prepared direct bonded copper (DBC) substrate using suitable die bonding techniques such as soldering or silver sintering. Subsequently, all gaps are filled with a high-temperature potting material. The resulting prepackage forms an easy-to-use power electronics building block.

The technique allows a high copper layer thickness, which paves the way for a considerable current carrying capacity. A big benefit is the high electrical and thermal contact area. The semiconductor's top and bottom side have ideal interconnections offering the full performance of the tiny WBG devices.

Different types of ceramic material are applicable including alumina, aluminum nitride or silicon nitride. The selection depends on the individual requirements for optimizing thermal management, mechanical properties, and cost.

For generating the trenches and cavities, subtractive manufacturing methods are used. The vias for the electrical contacts are drilled with a laser process. Then, they are filled with silver sintering material or similar conductive materials. The vias allow multi-layer ceramic substrate stacks, which are of particular advantage for low-inductance commutation cells.

Fraunhofer IISB is continuing its concentrated research on ceramic embedding and the necessary manufacturing process technologies to exploit the full potential of wide-bandgap semiconductor devices in power electronics. The goal is to bring the promising packaging technology to industrial production.

Fraunhofer IISB will showcase power modules based on its ceramic embedding technology on May 7-9, 2019, at the PCIM Europe exhibition in Nuremberg, Booth no. 438, Hall 6.