Recently, copper wires have been attracting much attention for LSI (Large Scale Integration) bonding because of its excellent mechanical and electrical properties, and low material cost. On the other hand, the end of these wires are usually joined to the pads or through-holes on the printed circuit board, and lead-free soldering is one of the popular bonding methods. Since the solders are weaker than copper wires, the stress and strain tend to be concentrated on the interface of solder/wire interface. The fracture frequently occurred there and may influence the quality of product. It is therefore important to evaluate the bonding strength of thin copper wire and lead-free solder. In this paper, pullout tests of thin copper wires from lead-free solder were carried out and the pullout behavior of the wires were observed. A method of bonding strength evaluation was proposed and the results were examined.
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