In selective welding, the flux coating process plays an important role. At the end of welding heating and welding, the flux should have sufficient activity to prevent the production of the bridge and prevent the PCB from producing oxidation. Flux spraying by the X/Y manipulator carrying PCB through the flux nozzle above, flux spraying to the PCB to weld position. Flux has a variety of ways of single-nozzle spray, microporous injection, synchronous Multi-point/graphic spray. After the reflow welding process, the microwave peak selection welding, the most important is the accurate spraying of the flux. Microporous injection will never stain an area other than a solder spot. Micro Point spraying minimum flux point graphics diameter is greater than 2mm, so spraying deposited on the PCB flux position accuracy of ±0.5mm, in order to ensure that the flux is always covered in the welded part above, spray welding dose tolerance provided by the supplier, the technical specification should specify the flux usage, usually recommended 100% safety tolerance range.