Soldering flux is used before and during soldering to prevent oxidation and create better, cleaner solder joints. This flux type: NC-559-ASM-UV is very popular in the electronics repair industry, used by many professionals.
The TBS Flux is a No-Clean solution which means it doesn’t require extra additional steps to clean the PCB after use. It comes in a 10CC syringe for ease of use. It includes a plunger and needle to help dispense the most precise amount for every delicate build.