Effects of crystallinity on mechanical properties of electroplated gold thin films used for three-dimensional electronic packaging

In this study, the effect of crystallinity, in other words, the order of atom arrangement of grains and grain boundaries in electroplated gold thin films on their mechanical properties was investigated by using electron back-scatter diffraction analysis, X-ray diffraction, and a nano-indentation test. The crystallinity of the electroplated gold thin film varied by changing the under layer materials: Cr/Pt/Au and Ti/Au, and annealing at 400 °C after electroplating. The variation of the microtexture caused the wide variation of mechanical properties of the electroplated gold films; Young's modulus fluctuated significantly from 79 to 113 GPa mainly depending on the crystallinity, and hardness also fluctuated from 0.90 to 2.75 GPa depending on the grain size. Therefore, it was confirmed that the control of the order of atom arrangement of electroplated gold films is indispensable for controlling the variation of mechanical properties and improving the reliability of electroplated gold bumps as a result.