Microstructure And Properties Of Deformed Pure Aluminum Foil Induced By Ultrasound

Aluminum, is one of the most co mmonly used materials in wire bonding tointerconnect, the chip with the lead frames to form electrical interconnections bythe wedge-shaped joints through ultrasonic vibrations. Its plastic deformationinduced by ultrasonic vibrations is particularly important to the formation andreliability of the joints. Therefore, the microstructure and texture of the foilmatrix deformed with different extents as a function of ultrasonic parameterswere investigated. And their microhardness, tensile properties and fracturefailure mode were analyzed. The variables were ultrasonic amplitude, ultrasonictime and deformation degree. The law of the microstructure evolution for thealuminum foil matrix was studied mainly by electron backscatter diffraction(EBSD) to obtain the orientation imaging maps, grain boundary maps,orientation distribution function(ODF); matrix microhardness and tensileproperties were measured and analyzed by a digital microhardness tester and anuniversal testing machine respectively; fracture failure mode was observed byusing scanning electron microscopy (SEM).The results showed that: after deformed by ultrasonic vibrations, thealuminum foil was refined. The average grain size was decreased from40μm inthe original to8μm in the deformed foil. The affect of the ultrasonic amplitudeand time was weaker than the deformation extent, but its overall trend was toincrease the degree of refinement and the misorientation. Along with the increaseof the deformation extent, grain refinement and misorientation were significantlychanged. Obvious recovery and recrystallization were followed when thedeformation extent of the aluminum foil reached50%, resulting in a lowergrowth of the deformation texture and a dispearance or even slightly rise of therecrystallization texture.Microstructures determines the performance and their evolution willinevitably be reflected in performances. To explore the effect of microstructuralevolution of the deformed aluminum foils on the microhardness and tensileproperties, serial plastic deformation extents of the aluminum induced byultrasonic vibrations were achieved. With the increase of the deformation extentin the aluminum foil, the microhardness firstly increased and then decreased. Thereason is that the grain refinement and the deformation texture lead to the earlyrise of the microhardness; with the enhancement of the ultrasound effect and therise of temperature, as well as aluminum itself which is high stacking fault energy metal, the defomation extent larger than25%resulted in an enhancedrecovery and recrystallization, and with growing of the recrystallization texture,the microhardness was decreased when the deformation extent further increased.The tensile properties had a similar trend, but it was shift at the peakcorresponding to the peak of the microhardness. That is because the grainrefinement was continued during the enhanced recrystallization, while both ofthem played a positive role in improving the tensile properties, resulting in thatthe peak of the tensile strength was delaed corresponding to that of themicrohardness.Combining the failure mode with the invers pole figure analysis, with theincrease of the deformation extent, the plasticity firstly increased, then decreasedsharply and finnally slowy recoverd. During its climbing stage, the dimples weresmall and deep, which was problbly rusulted from the processing strengtheningand the grain refinement. During its sharpely fallen stage, the dimples wereshallow and smooth because of its poor toughness, which was mainly caused bythe significant increase of the deformation textures and the serious decline of therecrystallization textures, and the severe fatigue and the increase of defects alsocontributed. With further increase of the ultrasonic vibrations, the temperatureincreased, and the recovery and recrystallization were enhanced. Some defectswere healed up, and the proportion of recrystallization texture got increased andthe proportion of deformation texture decreased, resulting in a slow recovery ofplasticity of the aluminum foil.