Effect of heat treatment on the shear strength and fracture modes of copper wire thermosonic ball bonds to Al-1% Si device metallization

The effect of bonding machine parameters and subsequent heat treatment in air or nitrogen atmospheres at 125°C, 200°C, and 300°C, for times up to 1000 h, on the shear strength of thermosonically ball-bonded copper wires to an Al-1% Si metallization on a silicon substrate, is investigated. The shear strength of the bonds formed at high power was always substantially higher than that of those formed at low power. Heat treatment in air generally increased the strength of bonds at low power. The strength decreased substantially for bonds formed at low power and heat treated in nitrogen at 125°C and 200°C. The full effect of annealing at any temperature was established after about 200 h. Detailed statistics of the mode of failure showed that fracture tended to occur at the copper/metallization interface, but this was influenced by the bonding power and heat treatment. Negligible interdiffusion occurred, and no intermetallic compounds were observed