Microstructure and mechanical properties of annealed Al-1%Si bonding wire

Abstract

The microstructure and mechanical properties of 1.25-mil diameter Al-1%Si bonding wire annealed at various temperatures and times have been investigated. The results indicate that the strength shows normal decrease with increasing time and temperature, but the elongation exhibits an unusual U-shaped variation. Of interest is a special point in annealing at a given temperature, that is, same strength (σ_s = σ_b = 150–160 MPa), same elongation (δ<0.2%), and same fracture surface. Annealed at a lower temperature (>300°C), the recrystallized structure has a fine annealing texture that possesses less elongation. At intermediate temperature (300–480°C), some grains grow to intersecting grains and form a mixed structure in which the elongation is about 3–6%. At temperature greater than 480°C, the grains grow rapidly to ultra-long grains. Single slip occurs easily in these ultra-long grains, resulting in lower strength and greater elongation (10–16%). For wire testing, the geometric factors of the wire play a very important role, affecting the microstructure and mechanical properties.