Thermomechanical stress and deformation effects in reactive Al/Ni multilayers for debonding

• Applicant: Professor Dr. Peter Schaaf
• Subject Area: Metallurgical, Thermal and Thermomechanical Treatment of Materials ; Synthesis and Properties of Functional Materials ; Mechanical Properties of Metallic Materials and their Microstructural Origins ; Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 426206394

The first project phase aimed at identifying the effects of mechanical and thermomechanical stresses and constraints on the transformation reaction and phase formation in Ni/Al multilayers. This included intrinsic and extrinsic stresses resulting from mechanical loading as well as stresses caused by geometrical confinements, such as passivation layers on multilayer films. So far, it could be shown that extrinsically applied stresses have no significant influence on the reaction behavior of the Al/Ni reactive multilayer system (RMS) and their phase formation. During the investigations, however, it was shown that after/during the reaction, crack formation, or delamination of the RMS takes place for certain substrates, especially on single-crystalline silicon. In addition, the reaction speed and temperature was changed that way. Thus, the intrinsic thermomechanical stresses during and after the reaction are much more important than extrinsic stresses. The next project phase will consider these intrinsic stresses and aims to exploit these intrinsic stresses for selective delamination of the films "at the push of a button", Therefore, the corresponding thermomechanical properties have to be characterized, and the tailored for debonding processes. Debonding and delamination applications are extremely important for dismantling and recycling in the field of microsystem technology. Individual components can only be separated from the overall system with difficulty or not economically and can thus be replaced, which strongly impairs sustainability and circular economy (resource saving). In the field of application, the integration of the RMS into a microelectronic system will be necessary. Besides the stress-induced delamination, detailed investigations of the long-term stability are necessary. Does aging of the RMS takes place and which time-temperature regimes the RMS can remain active in the system, i. e. maintain a self-propagating high-temperature synthesis. Furthermore, the RMS can be regarded as a functional connection in this case, which entails measurements of the thermal as well as electrical conductivity, mechanical properties of the layer structure as well as the compatibility in the context of a joining connection with low-melting solders (deposited galvanically or by magnetron sputtering) or separately added during the joining process. Subsequently, compatibility with low-melting solders will be investigated (joining part). It is further investigated whether ideally a second RMS can be used for the joining process Finally, investigations will be carried out on the complete system with regard to reliability and feasibility.

• DFG Programme: Research Grants