The adhesion strength of a lead-free solder hot-dipped on copper substrate

Eutectic Sn-Zn-AZ solder alloy was used [composition: 91Sn-9(5Al-Zn)] to investigate the effects of dipping parameters such as the temperature, rate and time dipping on the adhesion strength between Bolder and substrate using dimethylammonium chloride (DMAHCl) flux. The optimum conditions for the highest adhesion strength(about 8 MPa) were determined as dipping at 350 degrees C, and a rate of 10.8 similar to 11.8 mm/s for 5 similar to 7.5 min. A poor solder coating was obtained as dipped at 250 degrees C. Some defects by non-wetting were found as dipped at a slow rate (slower than 8.2 mm/s). Quite different from the most tin-based solders for copper substrate, gamma-Cu5Zn8 intermetallic compound particles were found by x-ray diffraction (XRD) analysis at the interface of solder and substrate as dipped at 300 degrees C after pull-off test by etching out the unreacted solder layer. The morphology of the intermetallic compound formed was observed by scanning electron microscopy (SEM). The elements of Al (near Cu), Zn (near Sn) are enriched at the interface of solder and copper substrate as determined by the line scanning and mapping analysis.