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Analysis of Technological Properties and Influencing Factors of Electronic Solder (Part II)
(2) Antioxidant Property of Liquid Solder
That is, the ability of liquid solder to resist oxidation reaction at a certain temperature. The oxidation of molten solder will not only cause serious waste of metals, but also hinder the bonding between the solder and the surface atoms of the base metal. It will also lead to various welding defects when the oxide film enters the weld. According to the theory of liquid metal oxidation, oxygen will be strongly adsorbed on the surface of liquid solder. At high temperature, the adsorbed oxygen molecule will be decomposed into oxygen atoms, oxygen atoms lose electrons and become ions, and then combine with metal ions to form metal oxides. The composition and structure of oxide film are different. The growth rate, growth mode and distribution coefficient of oxide in liquid solder will be different. Very large. The difference is closely related to the composition of solder. In addition, oxidation is also related to temperature, partial pressure of oxygen in gas phase, adsorption and decomposition rate of oxygen on solder surface, combining ability of surface atoms with oxygen, density of surface oxide film, dissolution and diffusion ability of products.
(3) Wettability of liquid solder
That is to say, at a certain temperature, the wetting speed and wetting force of liquid solder on the base metal. The poor wettability will lead to difficulties in brazing, and lead to false welding, false welding and de-welding, which will directly affect the mechanical and electrical properties of brazed joints, resulting in poor signal transmission, information distortion, poor sensitivity and low reliability.
(4) Diffusion of liquid solder
That is, the ability of liquid solder to flow and expand on the base metal surface at a certain temperature. The diffusivity and wettability of liquid solder are closely related, but they are different. Diffusion is the comprehensive expression of wettability and fluidity of liquid solder. In brazing process, if the diffusivity of liquid solder is poor, the solder will expand insufficiently in the welded area or produce voids in the weld, which will reduce the bonding area. It is also easy to bridge or tighten the weld joints and lead to short circuit. Obviously, factors affecting wettability and oxidation have an effect on diffusivity.
