Working Principals of Automatic Soldering Machines
The definition of soldering solder can be found that "wetting" is the protagonist in the welding process. The so-called welding is the use of liquid "solder" wet on the substrate to achieve the joint effect. This phenomenon is just like water falling on a solid surface. The difference is that the weld will solidify into a joint as the temperature decreases. When the solder wets on the substrate, theoretically, the metal bonds with the metal to form a continuous joint. However, under actual conditions, the substrate is eroded by the air and the surrounding environment to form a Layer oxide film to block the "solder", so that it can not achieve a better wetting effect. The phenomenon is that water is poured on a plate filled with grease, water can only be concentrated in some places, and cannot be uniformly and evenly distributed on the plate. If the oxide film on the surface of the substrate is not removed, even if it is barely coated with "solder", the bonding strength is very weak.
1. Different welding and gluing
When the two materials are bonded together by glue, the surfaces of the two materials adhere to each other because the glue gives a mechanical bond between them. Because the glue is not easily fixed between the two, the shiny surface is not as good as the rough or etched surface. Gluing is a surface phenomenon that can be wiped off the surface of the original when the glue is wet. Soldering is the formation of a metal chemical bond between the solder and the metal. The molecules of the solder penetrate the molecular structure of the surface metal of the substrate to form a strong, fully metallic structure. When the solder melts, it is also impossible to wipe it completely off the metal surface because it has become part of the base metal.
2, wetting and no wetting
A piece of greased metal sheet is immersed in water and there is no wetting. At this point, the water will form a spherical water droplet that will shake off, so the water does not wet or stick to the metal sheet. If the metal sheet is washed in a hot cleaning solvent, carefully dried, and then immersed in water, the water will completely diffuse to the surface of the metal sheet to form a thin and uniform film layer. It won't fall, ie it has already wet the metal sheet.
When the metal sheet is very clean, the water will wet the surface. Therefore, when the "solder surface" and the "metal surface" are also very clean, the solder will wet the metal surface, which is much more clean than the water. Metal sheets are much taller because there must be a tight connection between the solder and the metal, otherwise a very thin oxide layer is formed between them. Unfortunately, almost all metals oxidize as soon as they are exposed to air. This extremely thin oxide layer will interfere with the wetting of the solder on the metal surface. Note: “Solder” means 60/40 or 63/37 tin-lead alloy; “substrate” refers to the metal to be welded, such as PCB or part foot.
4, capillary action
If two clean metal surfaces are brought together and immersed in the molten solder, the solder will wet the two metal surfaces and climb upward to fill the gap between the adjacent surfaces, which is a capillary action. If the metal surface is not clean, there will be no wetting and capillary action, and the solder will not fill this point. When the printed circuit board of the plated through hole passes through the wave soldering furnace, the force of capillary action fills the hole through the hole, and a so-called "soldering tape" is formed on the printed circuit board, and the pressure of the tin wave is not completely soldered. Push this hole.
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