Interfacial microstructures and kinetics of Au/SnAgCu

The gold/lead-free solder system, or Au/SnAgCu is a potential flip chip interconnect solutions for fine-pitch applications. This paper studies the interfacial microstructures and initial isothermal solid–liquid interdiffusion kinetics during the first 3 s of bonding at 230–290 °C. As revealed by Scanning Electron Microscopy (SEM), different morphologies of AuSn, AuSn2 and AuSn4 are observed under different bonding conditions. The initial Au–Sn solid/liquid interdiffusion kinetics is discussed with respect to its microstructures. The rate of Au consumption is used as a measure of the rate of intermetallic compound (IMC) formation. The fitted power law relationship reveals kinetically that Au consumption follows the Arrhenius relationship with a time exponent of 0.5. Isothermal aging at temperatures between 125 °C and 165 °C gives rise to activation energies and the rate of Au consumption in solid–liquid interdiffusion to be two orders of magnitude faster than solid interdiffusion.