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Interface Matching and Phase-Transformation Nucleation During Laser Fabrication of Pb-free Solder Bumps
J. Huang, W-Q. Shi, Y-P. Xie, Y-Q. Li and F-J. An

Sn–Ag3.5–Cu0.7 Pb-free solder bumps were successfully fabricated on a copper clad laminate (CCL) surface by using a fiber laser system. The parameters of the laser apparatus used in the fabrication were laser power of 12 W, pulse frequency of 500 kHz, pulse duty factor of 50% and spot diameter of 0.03 mm. The fabrication result shows that the solder bumps formed by laser soldering were sufficiently and uniformly melted and securely joined with good properties. In this study, the spherical cap-type appearance of the solder bumps was theoretically interpreted from the perspective of the degree of lattice interface matching and it was demonstrated by non-spontaneous metal nucleation theory that the experimental parameters had been reasonably selected.

Keywords: Fibre laser, copper clad laminate (CCL), laser soldering, Pb-free soldering, filler metal bump

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