LongPower

Long product lifetimes and fewer rejects are the keys to significantly less waste. Hybrid electronic waste in particular has become a huge problem for people and the environment worldwide. Complete large appliances, such as washing machines or motors, are often thrown away because a relatively small electronic component no longer works because it is no longer connected correctly.

The LongPower project contributed to solving this problem by realising the construction of a demonstrator for the rapid holographic inspection of sophisticated power electronics. To this end, Fraunhofer IPM developed a new type of optical sensor and the Chair of Packaging Technology at IMTEK developed customised modules for the active and passive thermal excitation of power electronics.

The investigations in this project centred on IGBT chips (insulated-gate bipolar transistor). Due to the high collector-emitter voltage V_CE of over 650 V and the high current of more than 50 A, these are increasingly being used in the industry in power modules for converters. For the project, chips were placed on PCB substrates using modern sintering methods. The differences in the thermal expansion coefficients between the substrate, sintered layer and chip lead to deformations in the micrometre range under thermal stress and therefore often cause the module to fail. Based on the basic principle of digital holography/interferometry, a method for fast, time-resolved and simultaneous imaging measurement was investigated. Furthermore, a modern, high-speed ESPI system (Electronic Speckle Pattern Interferometry) for analysing and a heating system for passive excitation of the samples was designed and set up during the project. Based on the change in surface shape under thermal stress, conclusions could be drawn about production-related defects in the components. Active excitation was carried out using an existing load cycle rig at IMTEK.

In the course of the project, a quality testing system was thus established with which internal defects in power electronics can be clearly detected for thermal excitation based on the deformation mode.

Building on the LongPower demonstrator project, the LZN is also currently supervising the Longpower 4.0 scaling project, which aims to develop and transfer an industry-compatible holographic inspection system for 100% quality assurance in production.