Evaluation of Thin Copper Wire and Lead-Free Solder Joint Strength by Pullout Tests and Wire Surface Observation

Abstract

Abstract:Copper wires have been attracting much attention for Large Scale Integration (LSI) bonding because of their excellent mechanical and electrical properties, in addition to their low material cost. The ends of these wires are usually joined to pads or through-holes on a printed circuit board, and lead-free soldering is one of the popular bonding methods. Since the deformation resistance of solder is lower than that of copper, especially in slow deformation due to creep, the strain tends to be increased in the solder and concentrated near the copper/solder joint interface. Thus, fracture frequently occurs at this interface and may influence the quality of the 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 wire from lead-free solder were carried out, and the pullout behavior of the wires was observed. The bonding strength was evaluated based on the actual bonded area on the copper wire surface. Finally, the strength of the thin copper wire/solder joint was summarized using the shear and tensile strengths of the copper/solder interface as well as the tensile strength of the copper wire.

Microwave Soldering of Low-Resistance Conductive Joints—Technical and Economic Aspects

“…The evaluation of the tensile and shear characteristics of the soldered joints was performed using test method standards for lead-free solders [31][32][33][34]. An LBG TC 100 electromechanical computerized universal testing machine from LBG srl (Azzano San Paolo, Italy, 2009) was used for the tensile testing.…”

Welding characteristics of coated twisted wire and copper plate by ultrasonic vibration source using a transmission rod with helical slits

“…For example, the coating on coated wire must be removed before welding, the dielectric strength of coating of the coated wire decreases during heating, and both heating and cooling for welding take time. [6][7][8] Crimping is the most commonly used method to weld connector terminals and copper wire, but this results in the electric wires merely coming into contact with each other, not metallically welding. Therefore, oxide film and other impurities form at the welding interface, which tends to increase contact resistance.…”