The low temperature soldering process is required in the increased demand for flexible and wearable devices/substrates and to reduce the thermal shock damage caused by coefficient of thermal expansion (CTE) mismatch between solder materials and substrates during the soldering process. The low temperature laser soldering processes as an alternative to conventional reflow soldering processes owing to their advantages, such as local heating, non-contact heating, and short bonding time. In this study, we compared and evaluated the laser and reflow soldered joints using representative low melting temperature eutectic Sn-Bi solder balls and two types of surface finished Cu pad: thin electroless nickelelectroless palladium-immersion gold (ENEPIG) and organic solderability preservative (OSP). Laser soldering was performed using various laser powers (130, 150, and 170 W) and times (2 and 4 s). Furthermore, an aging test was carried out at 110°C for 2000 h to evaluate the long-term reliability of the soldered joints. The mechanical properties of the soldered joints were evaluated by conducting shear tests depending on aging time; in addition, the top-views, cross-sectional views, and fracture surfaces were also analyzed. In the case of OSP surface finished Cu pad, various shapes of initial intermetallic compounds (IMCs) were formed at the joints depending on the laser irradiation conditions. For the high power and long time, that is, relatively high energy applied conditions, thick and long initial Cu6Sn5 IMC was formed. On the other hand, for the low power or short time, that is, relatively low energy applied conditions, thin and short initial Cu6Sn5 IMC was formed. After the aging test for 100 h, Cu3Sn IMC was observed under all soldering conditions. In addition, IMCs thickness increased and shear strength decreased with aging time increased. Moreover, as the aging time increased, the brittle proportion increased. Hence, the fracture mode changed from an initial ductile fracture to brittle fracture (between the solder and IMCs) dominated. After the aging for 250 h, the reflow soldering condition continued to maintain a low shear strength and the widest brittle proportion up to aging for 2000 h. Additionally, after the aging for 2000 h, the reflow soldering condition showed the thickest total IMCs. In the case of ENEPIG surface finished Cu pad, various initial IMCs were formed at the interface depending on the laser irradiation conditions. In addition, the Cu and elements in the metallization layer reacted with Sn in the solder depending on the aging, and additional IMCs were formed and grown. Moreover, as the aging time increased, the fracture mode changed from the ductile fracture to brittle fracture (between the solder and IMCs and/or between the IMCs and Cu pad) dominated. For the reflow soldered condition, the superior shear strength was maintained until the aging for 500 h, but the shear strength sharply decreased thereafter. In addition, Bi segregation was observed after aging for 1000 h, resulting in shear strength decreased and inferior long-term reliability. For the laser soldering condition at 170 W for 2 s, shear strength gradually decreased with increased aging time and maintained a stable shear strength until aging for 2000 h. In ddition, Bi segregation was not observed under this condition. Therefore, the laser soldering method is more suitable for long-term reliability than the conventional reflow soldering method for two types of surface inished Cu pad.