Behavior of Anisotropic Conductive Film (ACF) Joint under Mechanical Shock

The contact resistances investigated by this study of ACF joints using $Au∕Ni$ bumps and flexible substrates are found to be increased by the induced mechanical shock and also by the combined effect of heat/humidity and the mechanical shock. The samples humidified at 85°C/85% RH for 384 h, on which a load of 3.164 Kg was dropped four times from a height of 0.4 m, exhibit the most severe results. The contact resistance increases by 700%, which had been about 62 mΩ in the as-bonded condition. The samples without humidification showed a sluggish and gentle increase in contact resistance with the induced mechanical shock. The contact resistance was found to be increased by 400% after the sixth drop from a height of 0.5 m. Scanning electron microscope images show particle deformation due to abrasion and friction between the contacting surfaces resulting from the sudden impact. Joints are also observed with no connections, which signify open circuits. Almost 25% of the circuits were found open in the samples (after 384 h in a humid environment), which have suffered severe mechanical shock (load drops four times from 0.4 m height). Breaking of the conductive layer of the particle and exposing the underlying polymeric portion were also observed.