Elastic properties of bonding wires

The development of microelectronics is strongly driven by requirements to reduce the dimensions of all components and, therefore, to increase the integration density and functionality. This leads, amongst others, to specific demands on the robustness and reliability of the interconnecting components used for the packaging technologies. In particular, miniaturized and/or highly stressed bonding wires need an increased stiffness and strength of the applied materials. In this context, we discuss the determination of elastic deformation properties of different gold and aluminum bonding wire materials and their relationship to the respective grain microstructure. It is shown that the Young´s moduli of bonding wires depend almost solely on the elastic anisotropy properties of the different grains. Thus, Young´s modulus can be directly calculated from grain orientation distribution as determined by appropriate electron backscatter diffraction analysis. Consequently, the results can be used for predicting the deformation properties and stiffness of bonding wires by a design of microstructure. Furthermore, it is possible to determine elastic properties also for process-affected wire sections like the heat affected zone and the free air ball, where no meaningful experimental mechanical testing of the elastic properties can be performed.