Gold wire bonding on low-k material: a new challenge for interconnection technology

The gold wire bond technology is still widely used in back end assembly. Even for conventional devices the wire bond technology applies mechanical stress on the bond pad and substrate layers, which leads to known damages like cratering and oxide cracks. The parameter combination of ultrasonic power and impact force may cause serious mechanical damage on the device. The wire bond technology is a trade off between proper interconnection on gold and aluminum and prevention of any mechanical damage on the stacks under the aluminum pad. Therefore it is crucial to control these parameters precisely in a defined and tight range. In terms of mechanical response on stress factors, low-k material is very sensitive. Wire bonding equipment needs to address this issue and must be designed for such a challenge. This investigation gave a first attempt to bond low-k material. Additional tests have to be carried out in order to study the effects of stress behavior, oxide cracks and also the influence of the bond parameter regarding different pad metal structures and low-k materials.