Poor solderability of circuit board holes will result in virtual soldering defects, affecting the parameters of components in the circuit, leading to unstable conduction of multi-layer board components and inner wires, and causing the entire circuit function to fail.

　　The so-called weldability refers to the property of the metal surface being wetted by molten solder, that is, the formation of a relatively uniform and continuous smooth attached film on the metal surface where the solder is located.

　　The main factors affecting the solderability of printed circuit boards are: (1) the composition of the solder and the properties of the soldered material. Solder is an important component of the welding chemical treatment process, which is composed of chemical materials containing flux. The commonly used low melting point eutectic metals are Sn-Pb or Sn-Pb-Ag. The impurity content should be controlled in a certain proportion to prevent the oxide produced by impurities from being dissolved by the flux. The function of solder is to help wet the surface of the soldered board circuit by transferring heat and removing rust. Generally, white rosin and isopropanol solvents are used.

　　(2) Welding temperature and surface cleanliness of the metal plate can also affect weldability. If the temperature is too high, the diffusion rate of solder will accelerate, and it has high activity, which will cause the melting surface of the circuit board and solder to quickly oxidize, resulting in welding defects. The contamination of the circuit board surface will also affect the solderability and cause defects, including tin beads, tin balls, open circuits, poor glossiness, etc.