Thermal aging effect on copper wire and micro interfacial frictional behavior along Cu FAB and Al pad

The aim of present research is to investigate the characteristic of ultra thin copper wire and aluminum pad. In the first, the electric flame-off (EFO) characteristic of ultra thin copper wire has been carefully examined. Experimental results show thermal aging effect has significantly influence on the micro structure of free air ball (FAB). Optical microscopic (OM) examination for an as-drawn copper wire (25°C) demonstrates the greatest strength on FAB and result in localize stressed area on Al pad under the smashed FAB. Secondary, micro interfacial frictional behavior along FAB and pad has been explored to study the influence on reducing the Al pad squeezing. The coefficient of frictional force at a tiny surface level was measured by Atomic Force Microscopy (AFM). It is also observed that the surface roughness is a major factor to reduce the Al pad squeezing. A 3D finite element wirebonding model based on ANSYS/LS-Dyna software was developed to predict large plastic deformation between Cu FAB and Al pad.