Study on wettability and defects behavior of flow-soldered joint using low residue flux

Effects of non-cleaning and cleaning fluxes on wetting properties and defects at flow-soldered joints were investigated. RMA-type flux of 15% solid content was used for cleaning flux, and R-type flux of 3.3% solid content for non-cleaning flux. A wetting test was conducted by the wetting balance method using a vertical flat Cu plate with various surface conditions: polished, non-polished, plated with Sn-37%Pb and oxidized. Sn-37%Pb eutectic alloy was used as solder. A flow soldering process was performed using both type of fluxes, and a visual inspection was carried out after soldering process. As experimental results reveal, wetting times of polished and Sn-37%Pb plated specimens were shorter than those of non-polished and oxidized specimens. Wetting time for using non-cleaning flux was short enough to be considered as having good wettability. Conveyor speed of printed circuit board (PCB) had great effects on the icicle and bridge defect regardless of flux-type. Conveyor speed of 1 m/min was optimum speed for cleaning flux, and in the case of the non-cleaning flux. 1-2 m/min was acceptable and preheating temperature affects the joint defect relatively less.