Hardness Measurement of Copper Bonding Wire

In semiconductor packaging industry, thin metal bonding wires, such as gold and copper, in the diameter range of 18 to 25 microns, are commonly used to connect between IC chip and connector pins through thermosonic and ultrasonic welding (bonding) in various types of packages. Copper bonding wire posts great challenges to industry users when they need to bond it onto IC bond pad of sensitive construction underneath. Any hard impact due to the material property, i.e. hardness, or excess ultrasonic parameter setting in the bonding process can easily cause the pad to crack. It is therefore of interest to the users on how hard the copper wire is and most importantly, the subsequent solidified molten ball as a result of melting the tip of the wire in the process. A Vickers micro-indentation hardness tester with minimum load of 0.5 gmf (5mN) capability is used to measure the hardness of copper wire along its length and in the free air ball (FAB). To determine the suitable load to be used to measure hardness of such fine diameter and minimize variation in the measured results due to different sample preparation effects, a range of load from 1 gmf to less than 50 gmf was studied.