Cu wire is increasingly used in microelectronics packaging manufacturing. In the present paper, the deforming procedure of 100 μm diameter Cu free air balls (FABs) is studied using experimental and finite element (FE) methods. Experimental results show that the superimposed ultrasound can make the Cu FAB softer. Then a non-linear FE model is built to study the deforming process of the Cu FAB. Numerical experiments have been carried out to quantify the effects of superimposed ultrasound on the constitutional model of Cu FABs. An improved power law material model is then established to take into the dynamic acoustic softening effects. A good consistency is achieved in numerically predicted and experimentally obtained deformations of the Cu FAB under various ultrasonic intensities.
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