Regensburg 2025 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 23: Phase Transformations

MM 23.3: Talk

Wednesday, March 19, 2025, 17:45–18:00, H23

Phase formation at an interface between Ni and Sn layers during a soldering process — •Sandra Gaertner, Sergiy V. Divinski, Harald Rösner, and Gehard Wilde — Institute of Materials Physics, University of Münster, Münster, Germany

Soldering is a method for creating permanent bonds between metal parts, often resulting in the formation of intermetallic compounds. The transition to lead-free solder, driven by environmental regulations, has increased the interest in Sn-based solder alloys. However, the soldering process for interconnects involves complex processes related to material transport, phase stability, phase formation, and kinetic aspects of phase transformation. In this study, we investigated the interdiffusion and diffusion-controlled phase formation in a SnSb-solder alloy between a Ni-based layer with a small amount of Si and a Cu substrate, employing SEM and TEM. Analysis of the untreated states revealed a lamellar-type structure of the Ni-based layer, characterized by a uniform distribution of elements, while the solder alloy exhibited a β-Sn matrix and a SbSn phase. Following the soldering process, we observed the formation of various intermetallic compounds like CuSnNi and SnCu, encased within the β-Sn matrix. The SbSn phase remained as small inclusions. Moreover, the Ni-based layer initially shrank, resulting in a residual thin film that displayed an increased Si content compared to its untreated counterpart. This study highlights the intricate mechanisms involved in Cu transport from the substrate through the solder material. Alongside Sn, Cu drives the transformation of the Ni-based layer, ultimately leading to its complete consumption.

Keywords: Sn-based solder; electron microscopy; intermetallic compounds; soldering