Highly efficient soldering of Sn-Ag-Cu solder joints using blue laser

Laser soldering has been widely used to connect electronic components to printed circuit boards (PCBs), owing to its significant advantages, including localized heating, noncontact heating, rapid temperature rise and fall, good controllability, and high adaptability. However, poor absorptivity of the metals involved is one of the main drawbacks of traditional infrared (IR) laser soldering. In this study, we constructed a novel blue diode laser soldering system to validate its higher heat efficiency compared to that of an IR diode laser. A comparative study of blue and IR lasers for Sn-Ag-Cu solder/PCB joints performed by varying the laser process parameters revealed that the blue laser enabled joint formation at a lower laser output power and irradiation time. Furthermore, miniature impact tests of the joints fabricated using the blue laser at 8 W and those fabricated using the IR laser at 14 W revealed comparable joint impact strengths. The comparability of the 8-W blue and 14-W IR laser processes was confirmed by microstructure observations. These experimental results proved that blue laser soldering exhibited 43 % higher efficiency than IR laser soldering. This increased efficiency was further successfully validated by measuring the light absorption rate on the solder and performing simple thermal calculations based on this measurement. These results clearly show that blue laser soldering can be used as a highly energy-efficient electronic packaging technology.