Research On High Strength And High Conductivity Copper Alloys For Lead Frame Used In Large Scale Integrated Circuit

With the development of large-scale integrated circuit, higher mechanical and electrical properties of copper alloys for lead frame are required. The ideal requirement for lead frame material properties is that tensile strength, hardness and electrical conductivity are more than 600MPa, 180HV and 80%IACS respectively. The copper alloy materials developed at the present time are difficulty in meeting the needs of high performance. So the study on the copper alloy material for lead frame used in the large-scale integrated circuit attracts much more attention.According to the strength mechanism and comprehensive property demands, the effect of alloying elements on copper alloy properties is analyzed. The optimal copper alloy is Cu-Cr-Zr for high strength and high conductivity lead frame materials used in integrated circuit.By transmission electronic microscope, aging precipitation phase transformation of Cu-Cr-Zr-Mg and Cu-Cr-Zr alloys was dealt with. After solid solution treated at 920℃ and aged at 470℃ for Cu-Cr-Zr-Mg alloy, the fine precipitation of an ordered compound CrCu₂(Zr,Mg) is found in copper matrix as well as fine Cr and Cu₄Zr. Aged at higher temperature the precipitate phases are completely transformed into Cr and Cu₄Zr. For Cu-Cr-Zr alloy at the early stage of aging, precipitate phase Cu₅Zr is formed. Aged at the same temperature for 6h, the precipitate phases are Cu₅Zr and Cr, which is associated with the peak hardness condition in the alloy. The precipitates are coherent with copper matrix. The strength 407MPa derived from coherent strengthening is almost identical with the experimental value 430MPa.Upon aging after solid solution for the Cu-Cr-Zr-Mg alloy, there could be linearity between electrical conductivity and volume fraction of precipitates. Based on the linear relationship, Avrami phase transformation kinetics equation and electrical conductivity equation at different aging temperatures are described for the Cu-Cr-Zr-Mg. The time-temperature-transformation (TTT) curves are also established.The mutual action between the aging precipitation and recrystallization and their effect on the microstructure and properties are dealt with systematically. Aged at the temperature lower than 550℃, it is found that the dislocations provide nucleation site for precipitation and the dispersed precipitates distribute along the dislocation, resulting in the precipitation hardening effect. At the same time the dislocations are pinned by the dispersed precipitates, the following recrystallization process is hindered. Rolled at definite extent of deformation and aged at higher temperature, the cell substructures formed by dislocation walls first appear strip structure. Then the bulging of the boundaries of some cell substructures and annihilation of the dislocations inside the cells indicate the onset and growth of recrystallization. The development of recrystallization offsets the hardening of the Cu-Cr-Zr alloys.For the first time, artificial neural network models of thermomechanical treatment processes and aging processes for Cu-Cr-Zr-Mg alloy and Cu-Cr-Sn-Zn alloy are established by...