Modeling of copper wire bonding ball transient temperature behavior

Copper wire has been widely investigated in recent years as an alternative material for gold wire bonding of electronic packaging. Compared to the gold wire, copper has a higher electrical conductivity and thermal conductivity, better mechanical property and much slower IMC growth. However the bondability of copper wire is weaker than gold, and poor bonding can further degrade the reliability of the products. Bonding material temperature is one of the key factors having a significant impact on the ball yielding deformation and the bondability. This report investigates the temperature evolution of the copper ball during the wire bonding process. Commercial software package FloEFD is used for the finite volume transient simulation. Melting and solidification of the copper ball is modeled with the equivalent specific heat method. Results of the transient ball temperature simulations show the cooling profiles with rapid solidification finished only 1 ms after the electronic flame off (EFO) firing. The solidification is followed by a rapid temperature drop to below 200degC within only 10 ms.