Necessary conditions for soldering PCB circuit boards

1.The weldment must have good weldability

The so-called solderability refers to the performance of the alloy that the metal material to be welded and the solder can form a good combination at the appropriate temperature. Not all metals have good weldability. Some metals, such as chromium, molybdenum, tungsten, etc., have very poor weldability; some metals, such as copper, brass, etc., have better weldability. During welding, the high temperature causes an oxide film to form on the metal surface, which affects the weldability of the material. In order to improve solderability, surface tin plating, silver plating and other measures can be used to prevent oxidation of the material surface.

2.The surface of the weldment must be kept clean

In order to achieve a good combination of solder and weldment, the welding surface must be kept clean. Even for weldments with good weldability, oxide films and oil stains that are harmful to wetting may be produced on the surface of the weldment due to storage or contamination. The dirt film must be removed before welding, otherwise the welding quality cannot be guaranteed. Mild oxide layers on metal surfaces can be removed by flux. Metal surfaces with severe oxidation should be removed by mechanical or chemical methods, such as scraping or pickling.

3.Use appropriate flux

The function of flux is to remove the oxide film on the surface of the weldment. Different welding processes require different fluxes, such as nickel-chromium alloy, stainless steel, aluminum and other materials. It is difficult to solder without a dedicated special flux. When welding precision electronic products such as printed circuit boards, in order to make the welding reliable and stable, rosin-based flux is usually used. Generally, alcohol is used to dissolve rosin into rosin water.

4. The weldment must be heated to the appropriate temperature

During welding, the function of thermal energy is to melt the solder and heat the welding object, so that the tin and lead atoms obtain enough energy to penetrate into the crystal lattice on the surface of the metal to be welded to form an alloy. If the welding temperature is too low, it will be detrimental to the penetration of solder atoms, making it impossible to form an alloy, and it is easy to form a false solder. If the welding temperature is too high, the solder will be in a non-eutectic state, accelerating the decomposition and volatilization rate of the flux, causing the quality of the solder to deteriorate, and in severe cases, Can cause the pads on the printed circuit board to fall off. What needs to be emphasized is that not only the solder must be heated to melt, but the weldment should also be heated to a temperature that can melt the solder.

5. Suitable welding time

Welding time refers to the time required for physical and chemical changes during the entire welding process. It includes the time for the metal to be welded to reach the welding temperature, the melting time of the solder, the time for the flux to work and the time for the metal alloy to form. After the welding temperature is determined, the appropriate welding time should be determined based on the shape, nature, and characteristics of the parts to be welded. If the welding time is too long, the components or welding parts will be easily damaged; if the welding time is too short, the welding requirements will not be met. Generally, the maximum time for each solder joint to be welded is no more than 5 seconds.