The influence of welding process parameters on the surface quality of welding is quite complex, mainly including the following key points:

　　1. Control of preheating temperature

　　The function of preheating: ① Fully volatilize the solvent in the soldering flux to avoid affecting the wetting of the printed board and the formation of solder joints when the printed board passes through soldering; ② Bring the printed circuit board to a certain temperature before welding to prevent warping and deformation caused by thermal shock. Based on our experience, the preheating temperature is generally controlled at 180 200 ℃ and the preheating time is 1-3 minutes.

　　2. Welding rail inclination angle

　　The inclination angle of the track has a significant impact on the welding effect, especially when welding high-density SMT devices. When the inclination angle is too small, bridging is more likely to occur, especially in welding, where the "shielding area" of SMT devices is more prone to bridging; If the inclination angle is too large, although it is beneficial for the elimination of bridging, the amount of solder eaten at the solder joint is too small, which is prone to false soldering. The inclination angle of the track should be controlled between 5 ° -7 °.

　　3. Wave crest height

　　The height of the wave crest may vary with the passage of welding work time, and appropriate corrections should be made during the welding process to ensure the ideal height for welding wave crest height. The tin pressing depth should be 1/2-1/3 of the PCB thickness.

　　4. Welding temperature

　　Welding temperature is an important process parameter that affects welding quality. When the welding temperature is too low, the expansion rate and wetting performance of the solder become poor, resulting in defects such as solder joints, pinching, and bridging due to insufficient wetting of the solder pads or component terminals; When the welding temperature is too high, it accelerates the oxidation of the solder pad, component pins, and solder, which is prone to false soldering. Generally speaking, the welding temperature should be controlled at 250+5 ℃.