Investigation of intermetallic compound formation, Kirkendall void nucleation and failure in solder joints

• Applicant: Professorin Dr.-Ing. Kerstin Weinberg
• Subject Area: Mechanics
• Term: from 2015 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 265705691

Microelectronic circuits units include several connections, in particular solder joints between different metal layers which hold the multi-layered unit in position. Aging of the solder alloy, formation of intermetallics (IMCs) along the electrodes as well as nucleation and growth of pores and cracks influence the properties of the joints and may significantly affect the life expectation of the whole circuit unit. Though this topic is of high practical relevance, by today most investigations of IMC growth in solder are observantly, preditive models for IMC growth, void nucleation and crack formation are not available. The goal of the proposed research project is to provide a numerical tool for simulations of intermetallic growth and long-term aging in solder-copper connections. To this end we will derive a coupled phase-field model of the solder's microstructure subjected to thermal, mechanical and electrical loading. The nucleation of Kirkendall voids, their subsequent growth to pores and the formation of cracks under the influence of typical loadings will be in the center of attention. Regarding the available experimental and thermodynamical data we plan to model pure Sn-solder balls and traditional eutectic Sn-Pb solder on copper pads. Both solder connections have two distinct IMCs, Cu6Sn5 in the bulk and along the interfaces and Cu3Sn along the copper pad. In conclusion, the project will lead to fully three-dimensional simulations of the system solder-ball-on-copper-pad which allow for predictions of phase decomposition, IMC growth, void nucleation and crack propagation in real world applications.

• DFG Programme: Research Grants