Harmonic Analysis of a Solder Paste under Large Amplitude Oscillatory Shear

Large amplitude oscillatory shear experiments, as an alternative measurement technique for nonlinear rheology, were performed using a cone‐plate rheometer with a solder paste. We found that odd harmonics appear in the stress waveform. A two‐segment, piecewise linear model was introduced to analyze the experimental observation. The procedure for calculating the crossover shear rate, the first and second region viscosity, and an apparent yield stress from harmonic amplitude data are shown. This technique observes a time‐dependent structural transition between the unsteady initial state and the secondary state. We found that the crossover time depends on shear rate amplitude and can be represented in the quadratic form of imposed shear rate.