Selective wave soldering flux nozzle can not only finish continuous spraying, but also be set as an economic way to stop spraying when circuit board is detected. The solvent composition of flux can prevent the crack caused by high temperature.
The preheating device is composed of heat pipe, and the circuit board is preheated before welding, which can reduce the temperature difference and avoid thermal shock. The preheating temperature is between 90-120 ℃, and the preheating time must be controlled properly. Preheating makes the flux monotonous (evaporation of water in the lost area) and out of the activated form. The solder solution is constantly in the active form in the solder bath, so that the surface of the surging solder is free of oxide layer on the wave crest. Because the PCB and wave crest are in the relative active form before, the flux is volatilized casually, and there is no bubble in the solder joint.
In the selective wave soldering process, the solvent component of flux will be volatilized when passing through preheater. So as to prevent the occurrence of cracking caused by high temperature gasification of solvent components when passing through the liquid surface, and finally avoid the potential quality hazard of tin particles. The slow temperature rise of the parts to be loaded with tin products when passing through the preheater can prevent the occurrence of component damage caused by the physical effect of sudden heat when passing through the wave peak.
Precautions for wave soldering in the process of solder joint forming: when PCB enters the front end (a) of wave crest, the base plate and pin are heated, and before the wave crest (b) is not separated, the whole PCB is immersed in solder, that is, it is bridged by solder, but in the moment of separating wave crest end, a small amount of solder adheres to the pad due to the effect of wetting force, and due to the reason of external tension, it will be presented to lead When the center of the line shrinks to the minimum state, the wetting force between the solder and the pad is greater than the cohesive force of the solder between the two pads. As a result, a full and round solder joint will be formed, and the surplus solder at the end of the wave crest will be separated. Due to the reason of gravity, the solder will fall back into the tin pot.