The factors affecting the quality of reflow soldering

The factors affecting the quality of reflow soldering are as follows

1. Influencing factors of solder paste
The quality of reflow soldering is affected by many factors. The most important factor is the temperature curve of reflow furnace and the composition parameters of solder paste. Now the common high performance reflow welding furnace has been able to control and adjust the temperature curve accurately. In contrast, in the trend of high density and miniaturization, solder paste printing has become the key to reflow soldering quality.
The particle shape of solder paste alloy powder is related to the welding quality of narrow spacing devices, and the viscosity and composition of solder paste must be selected properly. In addition, solder paste is generally stored in cold storage, and the cover can only be opened when the temperature is restored to room temperature. Special attention should be paid to avoid mixing the solder paste with water vapor due to temperature difference. If necessary, mix the solder paste with a mixer.

2. Influence of welding equipment
Sometimes, the vibration of the conveyor belt of reflow welding equipment is also one of the factors affecting the welding quality.

3. Influence of reflow welding process
After eliminating the abnormal quality of solder paste printing process and SMT process, reflow soldering process itself will also lead to the following quality abnormalities:
① In cold welding, the reflow temperature is low or the reflow zone time is insufficient.
② The temperature in the preheating zone of tin bead rises too fast (generally, the slope of temperature rise is less than 3 degrees per second).
③ If the circuit board or components are affected by moisture, it is easy to cause tin explosion and produce continuous tin.
④ Generally, the temperature in the cooling zone drops too fast (generally, the temperature drop slope of lead welding is less than 4 degrees per second).