When welding an electric soldering iron, the following four points must be achieved:
1. The welding surface must be kept clean
Even for weldable components, due to long-term storage and contamination, harmful oxide films, oil stains, etc. may form on the surface of the components. So, before implementing welding, it is necessary to clean the surface, otherwise it is difficult to ensure quality.
2. During welding, the temperature and time should be appropriate, and the heating should be uniform
When welding, heat the solder and the welded metal to the welding temperature, allowing the melted solder to wet and diffuse on the surface of the welded metal, forming metal compounds. Therefore, to ensure the firmness of the solder joints, there must be an appropriate welding temperature.
At a sufficiently high temperature, the solder can be fully wetted and diffuse to form an alloy layer. Excessive temperature is not conducive to welding. Welding time has a significant impact on the wettability of solder and soldered components, as well as the formation of the bonding layer. Accurately grasping the welding time is the key to high-quality welding.
3. Welding points should have sufficient mechanical strength
In order to ensure that the welded part does not fall off or loosen when subjected to vibration or impact, it is required that the welding point has sufficient mechanical strength. To ensure sufficient mechanical strength of the solder joints, the method of bending the lead terminals of the soldered components before welding is generally adopted. However, excessive solder accumulation should not be used, which can easily cause virtual soldering and short circuits between solder joints.
4. Welding must be reliable to ensure conductivity
To ensure good conductivity of the solder joint, it is necessary to prevent false soldering. Virtual welding refers to the situation where the solder does not form an alloy structure with the surface of the welded object, but simply adheres to the surface of the welded metal. When welding, if only a part forms an alloy while the rest does not, this type of solder joint can also pass through current in the short term, and it is difficult to detect problems with instruments. But with the passage of time, the surface without forming an alloy will be oxidized, and at this point, there will be a phenomenon of intermittent on and off, which will inevitably cause quality problems in the product.
In short, high-quality solder joints should be bright and smooth; The solder layer is uniform, thin, and moist, with a suitable proportion to the size of the solder pad, and the contour of the joint is faintly visible; Sufficient solder, scattered in a skirt shape; No cracks, pinholes, or solder residue. The appearance of a typical solder joint is shown in Figure 8, where the height of the "skirt" shape is approximately 1 to I.2 times the radius of the solder pad.
