2D and 3D material morphologies for reactive microjoining in electronics

• Applicants: Dr.-Ing. Heike Bartsch; Professor Dr. Peter Schaaf
• Subject Area: Synthesis and Properties of Functional Materials ; Coating and Surface Technology ; Mechanical Properties of Metallic Materials and their Microstructural Origins ; Metallurgical, Thermal and Thermomechanical Treatment of Materials ; Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 426362670

The application of self-propagating reactions for the joining of electronic components in electronics and nanotechnology would allow fast joining with a local heat input, e.g. in electronic packaging. However, the self-propagating reaction after multilayer ignition is hard to control and thermo-mechanical stress is generated at the bonding interface. The proposed project aims to continue the research based on the results obtained in running first period. The effect of the substrate surface topography on the morphology of the produced reactive multilayers systems (RML) and its consequently influence on the behavior and self-propagation of the reaction of the Al/Ni RML was evidenced in the first phase of the project. However, these effects need to be transferred to materials of special interest for microtechnology (Si, Cu, glass, PMMA, Alumina). The aim of the project is to investigate the impact of the morphological characteristics, and physical properties of the joining partners on the microstructural features of the fabricated RMS, as well as, in the thermophysical properties of the system and in the kinetics of the reaction. Final goal is a “suitable” microjoining process with fitting electrical and thermal properties of a high-quality mechanical joining. The focus is the modification of surfaces towards well-defined geometrical or random morphologies. It is expected that the surface topography in combination with the physical properties of the substrate, will influence the growth of the multilayers during the sputtering affecting the microstructural characteristics of the Al/Ni RML. The substrate properties could change the heat transfer conditions during the self-propagating, changing its velocity and the maximum temperature. The cooling rate of the reacted material will be affected as well; hence, the resulting microstructure and morphology of the reaction products. Strategies for sequential and parallel ignition can be used to locally control the heat distribution, preheating, and cooling rates. Bonding experiments of samples with tailored surface morphologies and different chip-substrate combinations will allow the analysis of the bonding quality and defect analyses of the bonded area. This investigation will help to establish application rules for the selection of appropriate surface structuring and RML design for high-quality joining processes. It will give deep insights into the use of different architectures for chip joining and fosters the development of pre-designed layer structures for future joining at the microscale in electronics packaging. The derivation of design rules for substrate morphology, 3D geometries and multilayer architecture with regard to reliable chip joints in electronic systems will contribute to this goal. The results will allow a tailored packaging architecture for reactive electronic chip mounting in the future.

• DFG Programme: Research Grants