Automotive IQ sat down with Mr. Matthias Petzold , Head of Business Unit, Center for Applied Microstructure Diagnostics CAM, at Fraunhofer IMWS Halle, and discussed failure analysis techniques for power electronics packaging, the main challenges and advantages related to 3D packaging and reliability of packaging of SiC power components. 

Q1. – Prof. Petzold, you are the leader of the department of Components of Microelectronic and Microsystem Engineering at the Fraunhofer IMWS institute. Please describe in a few sentences, what aspects of power electronics you investigate and how long have you been involved in this area?

We are dealing with microstructure diagnostics of electronics components and materials, with particular focus on physical failure analysis. This means that our research activities aim at understanding the material interactions, defect risks and degradation mechanisms occurring within the technological processes and during application, particularly within the automotive domain. In close cooperation with our partners in industry results are used to consider and to prevent potential reliability risks already during the design and the qualification stage. In addition, our work contributes to secure the quality and to improve manufacturing yield during mass fabrication. In case of field returns we have to analyze any single event in detail to confine any resulting lifetime problems. In general, our work is focused on accelerating time-to-market of our partners’ innovative technologies and systems, on securing quality and reliability, thus improving cost structure and market potential of new technologies and products.

Q2. – You have conducted some very interesting work on failure analysis techniques for power electronics packaging. Can you tell us a bit about this work and what you have achieved in terms of investigating the reliability question?

Our work in power electronics packaging has been focused on understanding material interactions in reliability-critical contacting and encapsulation technologies. This includes for example, lifetime aspects of new heavy wire bonding materials, defect and quality risks of new die attach technologies such as e.g. silver sintering, corrosion mechanisms deteriorating the lifetime of automotive electronics components, or the relationship between the microstructure of encapsulation and housing materials and their electrical insulation properties. Together with equipment suppliers we are also working on new material diagnostics methods and tools that can be used for problem-adapted quality control and improved failure diagnostics methods, such as innovative non-destructive diagnostics and preparation tools.

Q3. – There has been a lot of investigation on reliability of packaging of SiC power components, however for SiC or GaN a lot of questions are still open. What are, in your opinion, the main differences between the former and the latter and what are the current directions for tackling these challenges?

SiC and GaN semiconductors offer new potential for power electronics, particular regarding superior voltage blocking capacity, reduced losses, and the capability of operation at higher temperatures and at higher switching frequencies. On the system side these properties result also in significant advantages for system integration and miniaturization, e.g. due to reducing the effort for passive components, saving both space and cost at increased functional performance. Considering the specifically high challenges in automotive applications, several questions regarding the reliability properties, also on the semiconductor side, remain to be solved. With respect to packaging it will be important to provide new solutions for thermally more robust contact and encapsulation materials and technologies. To secure the robustness of the system is key to fully utilizing the potential of wide bandgap semiconductors for operating at higher temperatures as well as for improving miniaturization and integration.

Q4. – One of the newest developments in power electronics packaging is 3D integrated packaging. Can you please explain a bit what 3D packaging means and what are the challenges and advantages in the automotive domain?

3D Integrated Power Packaging is related to the move from 2D side-by-side packaging of discrete components on a board to integration techniques employing vertical stacking of components and modules within a subsystem. As one example, innovative solutions are currently introduced into the market that allow 3D embedding of power switches, logic electronics, passives and the thermal management, such as integrated heat spreaders or cooling solutions, within a multilayer board or a module. In general, these approaches allow reducing size and weight, and improving power efficiency as well as electrical performance. A main task that is particularly significant for automotive applications consists in mastering the related new reliability challenges due to e.g. the increased thermal stress on logics, passives and packaging materials, and to secure the robustness of the new contacting solutions used for embedding technologies, such as Ag sintering. This needs also a deep understanding of the material reactions and potential degradation risks occurring in manufacturing and during use.

Q5. - You will be holding a presentation at the Advanced Power Electronics for EV/HEV conference in Munich on September 6th 2018. Can you tell us a bit about the contents?

The presentation discusses the role of microstructure diagnostics for “Physics of Failure”-oriented qualification and robustness validation concepts to secure quality and reliability properties of power electronics components in automotive applications. The application of current physical failure analysis methods will be illustrated by examples from research on power electronics packaging and on GaN components. This includes microstructure analysis of the interaction between operational stress and defect risks in GaN semiconductors, of the defect modes and quality factors in Ag sintered interfaces as an example for a new packaging process developed to optimize reliability and thermal robustness, and of aspects that affect the insulation reliability of power packaging encapsulation materials stressed by humidity and electrical fields.