① Stimulate the activity of the flux and remove the surface oxides of the welding material;
The role of the flux must be familiar to everyone. The flux can remove the surface oxides of the PCB circuit board pads and electronic components. When the welding material is in contact with the air for a long time, the welding material will undergo an oxidation reaction due to the influence of moisture in the air. After preheating, the flux can activate the activator component of the flux and remove the oxides on the surface of the material. In addition, there are some solvent components in the flux that are more volatile. After preheating, these solvent components will be volatilized by preheating, thereby avoiding welding quality problems such as cold solder joints and sharp edges caused by these components during welding.
② Reduce the thermal shock of welding materials;
The welding temperature of wave soldering can reach above 240℃. If it is not preheated, the PCB will explode and bend due to thermal shock, and the heat-sensitive components will also be damaged due to thermal shock. Because the temperature in the preheating zone rises gradually, the PCB and electronic components can gradually adapt to the high temperature environment to reduce the impact of the PCB and electronic components under high temperature.
It should be noted that the preheating requirements of wave soldering should be strictly followed during preheating. The preheating time should not be too long or insufficient, and the preheating temperature should not be too high or too low. If the preheating temperature is too low or the time is insufficient, the volume components in the flux cannot be completely released. If the preheating temperature is too high or the preheating time is too long, the active agent components of the flux will be excessively volatilized, making the flux insufficiently active.
