When hot liquid solder dissolve and penetrate into the surface of the metal being welded, called tinning metal or metal soldering. Molecules form a new part of a mixture of solder and copper is copper, solder alloy, this solvent effect called wetting it in between the various parts constituting the bond between the molecules, the total of compounds to generate a metal alloy. Good intermolecular bond formation is the core of the welding process, which determines the strength and quality of the Welding Wirespoint. Only the surface of the copper is no pollution is not due to the exposure of the oxide film formed in the air in order to wetting, and soldering with the working surface need to reach the proper temperature.

2 surface tension

Everyone familiar with the water surface tension, this force so that the grease-coated metal plate of cold water droplets to maintain the spherical, This is because in this case, so that the liquid on the solid surface tends to the adhesion of the diffusion is less than their cohesion. With warm water and cleaning agent to reduce its surface tension, the water infiltration and form a thin layer of a metal plate coated with a grease to the outflow, if the adhesion is greater than the cohesion This occurs.

Sn - Pb solder cohesive force even greater than that of water, so that the solder was a sphere, in order to minimize their surface area (the same volume of the case, compared to the sphere and the other geometric shape having the smallest surface area to meet the demand for the lowest energy state) . The role of the flux cleaning agents the role of the metal plate coated with grease-like, Further, the surface tension is also highly dependent on the degree of cleaning of the surface and temperature, only the adhesion energy is much larger than the surface energy (cohesion) can occur, the ideal stick tin.

The third metal alloy of the production of compounds

Copper and tin metal bond formation between the duration and strength of the grains, grain shape and size depends on the welding temperature. Welding, less heat may be formed in a fine crystalline structure, the formation having the optimum strength Excellent welding points. The reaction time is too long, whether it is due to the welding time is too long, or because the temperature is too high, or both, will result in a coarse crystalline structure, the structure is a sandy and gravelly and brittle hair, less shear strength.

Hardware manufacturing concern that the use of copper as the metal substrate, tin - lead as the solder alloy, lead and copper is not formed any metal alloy common compounds, however, tin can penetrate into the copper, tin and copper intermolecular keys the connecting surface of the solder and the metal forming the metal alloy Total of physical Cu3Sn and Cu6Sn5 is. Metal alloy layer (n-phase + ε phase) must be very thin, laser welding, a metal alloy layer thickness of the order of 0.1mm, wave soldering and manual soldering iron, the thickness of the key between the the excellent Welding Cable point metal majority of more than 0.5μm. Since the shear strength of the welding point is reduced with the increase in the thickness of the metal alloy layer, it is often try to maintain the thickness of the metal alloy layer of 1μm or less by the weld time as short as possible, which can be realized.

Metal alloy Total thickness of the material layer is dependent on the formation of the weld point the temperature and time, the ideal case, the soldering should be 220't within about 2s completed, the chemical diffusion of copper and tin in this condition, the reaction will produce an appropriate amount of the metal The alloy bonding material Cu3Sn and Cu6Sn5 thickness of approximately 0.5μm. Insufficient intermetallic bond common cold welding points or welding is not elevated to the soldering point to a suitable temperature, it may lead to the cutting of the welding face. In contrast, thick metal alloy layer, common in excessive heating or welding too long welding point, it will cause the weld point to tensile strength is very weak.

4 wetting angle

Higher by about 35 ° C than the temperature of the eutectic point of the solder, when coated with a drop of solder placed on the heat flux on the surface, to form a meniscus, in part, the ability of metal surface wetting can be evaluated by the shape of the meniscus. If the solder meniscus bottom trimming, shaped like coated with grease metal plate drops, or even tends to be spherical, the metal can not be welded. Only the meniscus stretched into a less than 30. The small angle of only having a good weldability.