What are the factors that affect the quality of reflow soldering in SMT chip processing?

1. Influencing factors of solder paste
The quality of reflow soldering is affected by many factors. The most important factors are the temperature profile of the reflow oven and the composition parameters of the solder paste.

Nowadays, the commonly used high-performance reflow soldering furnace can accurately control and adjust the temperature curve more conveniently.
In contrast, in the trend of high density and miniaturization, the printing of solder paste has become the key to the quality of reflow soldering.


The particle shape of the solder paste alloy powder is related to the soldering quality of narrow-pitch devices, and the viscosity and composition of the solder paste must also be selected appropriately. In addition, the solder paste is generally stored in refrigeration, and the lid can be opened after returning to room temperature when taking it. Special attention should be paid to avoid mixing the solder paste with moisture due to temperature differences. If necessary, use a mixer to stir the solder paste evenly.

2. The influence of welding equipment
Sometimes, excessive vibration of the conveyor belt of the reflow soldering equipment is also one of the factors that affect the quality of the soldering.

3. The influence of reflow soldering process
After eliminating the quality abnormalities of the solder paste printing process and the placement process, the reflow soldering process itself will also cause the following quality abnormalities:

  • Cold welding is usually caused by low reflow temperature or insufficient time in the reflow zone.
  • The temperature rise in the preheating zone of the tin bead is too fast (generally, the slope of the temperature rise is less than 3 degrees per second).
  • Continuous tin circuit boards or components are damp, and excessive water content may cause tin explosion to produce continuous tin.
  • Cracks are generally caused by excessively rapid temperature drop in the cooling zone (generally, the temperature drop slope of lead soldering is less than 4 degrees per second).

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