Study On Microstructure Evolution And Texture Changes Of Drawing Aluminum Wire Under Ultrasonic

Aluminum wire is one of main materials for interconnection used in wire bonding, which can realize interconnection between the chip and external circuits under the effect of ultrasonic, the microstructure and performance of aluminum wire in wire bonding have significant effect on the quality and reliability of electronic packaging. Therefore, the microstructure evolution and texture changes of drawing aluminum wire under different ultrasonic process parameters were studied in the paper. In our experiments the evolution discipline of the microstructure and texture of aluminum wire under different ultrasonic amplitude and pre-deformation were studied through Orientation Imaging Map,Reverse Pole Figure and Misorientation Distribution of EBSD technology. The elastic modulus and hardness values of aluminum wire under different ultrasonic amplitude were measured with Nanoindentor and digital micro hardness tester respectively. Whether the deformation twinning in micro scale could appear or not in aluminum wire under all our ultrasonic experimental conditions was studied. The microstructure evolution and texture changes of drawing aluminum wire under different extrusion conditions and different heating conditions were studied in order to explore the mechanism of ultrasonic on the deformation of aluminum wire.The results show that the phenomena of dynamic recrystallization in drawing aluminum wire are very obvious in ultrasonic experiment. It was found that the increase of ultrasonic amplitude would promote the recrystallization of aluminum wire evidently, and it could also increase the proportion of small angle grain boundaries in aluminum wire heavily. The microstructure of aluminum wire is determined by both ultrasonic amplitude and the microstructure of primary aluminum wire. The original aluminum wire shows strong <111> texture in the axial direction of aluminum wire and weak <101> texture in the radial direction of aluminum wire and the direction perpendicular to the cross section of aluminum wire. The deformed aluminum wire shows <100> recrystallization texture in all three macro characteristic directions under 65% amplitude ultrasonic, and it shows <101> texture in the radial direction of aluminum wire and <111> texture in the direction perpendicular to the cross section of aluminum wire due to the pressure of ultrasonic equipment.The role of ultrasonic on the deformation of aluminum wire would be more obvious with the increase of the pre-deformation of aluminum wire, and the recrystallization of aluminum wire begins from the upper and under portion of aluminum wire. When the pre-deformation is smaller, the microstructure changes can be found only in parts of aluminum wire; when the pre-deformation is larger, the microstructure changes can be found in the whole aluminum wire. The microstructure of fully recrystallized aluminum wire consists of equiaxial grains, but the sizes of the equiaxial grains are uncertain due to the irregularity of deformation. The aluminum wire may show single <111> texture or show <100> and <111> mixed texture in the axial direction of aluminum wire.In order to explore the mechanism of dynamic recrystallization of aluminum wire under ultrasonic, the microstructure evolution and texture changes of aluminum wire under different extrusion conditions and different heating conditions are studied in this paper. The results show that the phenomena are all different from that of the aluminum wire in ultrasonic experiments. That can prove that the pressure and the high temperature are not the main reason of the recrystallization of aluminum wire during the ultrasonic-induced deformation. By comparing all the experiment data, we can know that it can probably conclude that the ultrasonic could promote the recrystallization of aluminum wire obviously. The possible reasons are as follows: the metastability of drawing aluminum wire,the instantaneous high temperature of aluminum wire,the softening of aluminum wire under ultrasonic and the gradient of sound pressure due to the interaction of ultrasonic and aluminum wire.