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Welding method and technique for printed circuit board

Date:2016-09-29

  When the hot liquid solder is dissolved and penetrated into the surface of the metal to be welded, it is called the dip of the metal or the metal to be stained with tin. A mixture of molecules with copper solder to form a new part is copper, part of solder alloy, the solvent effect is called tin, it forms intermolecular bonding between the various parts, generating a total of metal alloy. The formation of a good intermolecular bond is the core of the welding process, which determines the strength and quality of the welding point. Only the surface of copper is not contaminated, not due to exposure to the formation of the oxide film in the air can be stained with tin, and the solder and the work surface need to reach the appropriate temperature.

2 surface tension

Everyone is familiar with the surface tension of water, the force of coating metal plate with grease on the water droplets to keep ball, this is because in this case, the solid surface tends to be less than the liquid diffusion adhesion cohesion. Clean with warm water and detergent to reduce the surface tension, the water will be infiltrated with grease metal plate to form a thin layer of the outflow, if the adhesion is greater than the cohesion will happen.
Tin lead solder cohesion and even greater than water, the solder is sphere, to minimize surface area (the same volume, the sphere and other geometric shape compared with minimum surface area, to meet the needs of the lowest energy state). The effect of flux is similar to the cleaning agent on the metal plate coated with grease effect, in addition, the surface tension is highly dependent on the clean degree and surface temperature, only the adhesion energy is far greater than the surface energy (cohesion), can be the ideal tin.

3 generation of metal alloy Co

Copper and tin intermetallic formed the grain, the shape and size of the grain depends on the duration and strength of the temperature. The fine grain structure can be formed when the heat is less, and the best welding point with the best strength is formed. The reaction time is too long, whether it is due to the welding time is too long or the temperature is too high or both, it will lead to a coarse grain structure, the structure is gravel and brittle, shear strength is small.

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