Hybrid solder became the centre of attention after its capabilities to prevent warpage by decreasing the process temperature. Hybrid solder also known as mixed assembly solder, which assemble of high and low melting temperatures of solder in one solder joint. This research focused on the reliability determinisations of the hybrid solder, SAC305/Sn-58Bi, based on the thermal and mechanical behaviour of the solder including intermetallic compound (IMC) layer of the solder were observed. Under morphology observation, the IMC layer of hybrid solder was thinner 11.83 µm than conventional solder. Due to the high content of Bi in Sn-58Bi in hybrid solder, the presence of Bi-rich segregation was found above the interfacial layer and Bi-rich partially warped the SAC305 solder ball. Thermal analysis discovers that the hybrid solder has a lower process temperature, 190.47 °C compared to conventional solder (SAC305), 196.68 °C. Under high and low shear speed tests, the shear strength of hybrid solder was higher than conventional solder after reflowed on Cu-OSP. Hybrid solder shows higher reliability if solder with low process temperature and higher mechanical performance. Thinner IMC layer with segregation of Bi-rich above the layer improve the reliability of the solder.