Effect of thermomechanical treatments on microstructure and properties of Cu-base leadframe alloy

Abstract

The effect of thermomechanical treatments (TMT) on the microstructuresand properties of Cu-1.5Ni-0.3Si-0.03P-0.05Mg leadframe alloy wasinvestigated. The Cu-base leadframe alloy was received as hot rolledplates with 8 mm thickness. The hot rolled plates were solutiontreated at 700°C or 800°C for 1 hour, and coldrolled with 40–85% reduction, then followed by aging treatment at450°C. The leadframe alloy solution treated at 800°Cshowed larger grain size of 15 μm comparing with the grain size of10 μm in leadframe alloy solution treated at 700°C. Theleadframe alloy with smaller grain size of 10 μm showed highertensile strength and lower electrical resistivity than that withlarger grain size of 15 μm. The dislocation density increased withincreasing reduction ratio of cold rolling from 40% to 85% andresulted in finer Ni₂Si precipitates. Tensile strength increasedand electrical resistivity decreased with increasing reduction ratioof cold rolling due to the formation of finer Ni₂Si precipitates.Two types of thermomechanical treatments were performed to enhance theproperties of leadframe alloy. One type of thermomechanical treatmentis to refine the grain size through the overaging, cold rollingfollowed by recrystallization. The recrystallization process improvedthe tensile strength to 540 MPa and elongation to 15% by reducing thegrain size to 5 μm. The other type of thermomechanical treatmentis to refine the precipitate size by two-step aging process. Thetwo-step aging process increased the tensile strength to 640 MPa andreduced the electrical resistivity to1.475 × 10⁻⁸ Ωm by reducing the size of Ni₂Si precipitates to 4 nm.