Early stage growth characteristics of Ag3Sn intermetallic compounds during solid–solid and solid–liquid reactions in the Ag–Sn interlayer system: Experiments and simulations

Abstract

Transient Liquid Phase Bonding (TLPB) makes use of the isothermal solidification of a liquid interlayer through the formation of intermetallic compounds (IMC). This work investigates the Ag3Sn IMC formation in a thin, electroplated Ag–Sn interlayer system appropriate for TLPB – while covering as-coated conditions, growth initiation up to a few minutes of holding time – with experimental and numerical methods. Both solid-state and solid–liquid reactions at 200, 250 and 300°C, respectively, were covered under identical and near-isothermal conditions with a novel experimental setup. Morphological aspects like the lateral IMC grain size or the scallop roughness were proven to strongly depend on temperature. Growth kinetics were captured by power laws, growth exponents n were determined as 0.24, 0.36 and 0.29, parabolic growth constants k as 1.32⋅10−11, 4.04⋅10−10 and 7.24⋅10−10cm2/s at 200, 250 and 300°C, respectively, and the activation energy Q as 30.6kJ/mol. Predominant diffusion mechanisms, i.e. volume or GB diffusion, as well as coarsening effects were identified as temperature and time dependent at early stages. A mathematical model was developed based on the Arrhenius relationship including a growth correction function zIMC,corr to calculate and predict IMC growth as a function of temperature and time. The study was completed by multiphase-field simulations which targeted to mimic kinetic and morphological features of Ag3Sn IMC under various conditions. Good agreement between experiments and simulations was found for a limited set of parameters which allowed drawing conclusions about the dominant transport mechanisms for the reacting elements.