Improvement of Joint Reliability of Sn-Ag-Cu Solder Bumps on Cu by a Laser Process

摘要

Laser soldering has recently been introduced in industry because of its unique properties, which include localized and noncontact heating, a rapid rise and fall in temperature, and easy automation compared to reflow soldering. In this study, the effect of an annealing treatment on the impact strength of solder bumps heated using the laser process was investigated to improve the impact reliability of soldered joints. It was found that, in the as-soldered condition, a thin intermetallic compound (IMC) layer was formed at the interface of the solder bumps on a Cu pad when using the laser process with and without annealing. After aging at 150 degrees C, the impact reliability of the solder bumps heated using the laser process with annealing was superior to that of the solder bumps heated using the laser process without annealing. This was because the IMC grains at the interface clearly grew to a large size. These were effective at preventing Cu atoms from diffusing to the interface of the joints soldered by the laser soldering process and may be the reason that the annealing treatment at 20W for 5 s prevented the degradation of the maximum load of solder bumps when using the laser soldering at 40W for 1 s.