Fraunhofer IISB / PCIM Ceramic Embedding for Wide Bandgap Semiconductors

Power module made with the Ceramic Embedding technology.
Power module made with the Ceramic Embedding technology.

The limiting factor in power electronics often is packaging. This is especially true for the new wide bandgap semiconductors. Scientists at Fraunhofer IISB have developed a novel packaging concept by embedding power semiconductor devices into ceramic circuit carriers.

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

Ongoing miniaturization, 3D integration, and extreme environmental conditions impose major challenges to future power devices, modules, and systems, which are expected to provide excellent performance, high reliability, and long lifetime. Low cost is a key, enabled by high temperature. This implies small chip size and low cooling effort. In this respect, the applicability of established packaging technologies, e.g., based on PCBs (Printed Circuit Boards), is limited as they do not afford sufficient thermal stability or current carrying capability.

As a remedy, a novel packaging concept was developed at Fraunhofer IISB. It is based on the embedding of power semiconductors in ceramic circuit carriers. The scientists claim that their design offered high temperature stability, operation at high voltages, and hermetic sealing to provide maximum lifetime in harsh environments. Also the issue of undesired parasitic inductance can be enhanced. Power modules based on this new approach are presented by Fraunhofer IISB at this year’s PCIM Europe exhibition in May 7th to 9th, 2019 in Nuremberg (Hall 6, Stand 438).

With the new technology – called Ceramic Embedding – the power devices are placed inside a special prepared direct bonded copper (DBC) substrate by suitable die bonding techniques such as soldering or silver sintering. Subsequently, all gaps are filled with a high-temperature potting material. The resulting prepackage is forming an easy-to-use power electronics building block. The concept allows a high copper layer thickness, which paves the way for a considerable current carrying capacity. A big benefit is the big 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 such as alumina, aluminum nitride or silicon nitride. The choice depends on the individual requirements for optimizing the thermal management, mechanical properties, and cost.

For generating the cavities and trenches, 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 the realization of multi-layer ceramic substrate stacks, which are of special advantage for low-inductance commutation cells.

Fraunhofer IISB is continuing its research on Ceramic Embedding and the necessary manufacturing process technologies. The target is to bring the promising packaging technology to industrial production.