Analysis of the process performance and influencing factors of electronic solder (above)
Release time:
2022-09-27
【Summary Description】 The process performance of solder refers to its performance during use. According to the investigation, the technical problems encountered in the process of electronic soldering are mainly the behavior of liquid solder. The wetting, flow, filling and spreading of liquid solder on the surface of solid base metal are the premise of brazing. Without this premise, even if the physical, mechanical properties and microstructure of the solder are better, it is futile. In the process from melting to solidification and crystallization, the various properties of the solder are interrelated and influenced. For example, the melting temperature of solder determines the temperature range of brazing, and the difference between the solid and liquidus temperatures of solder determines the speed of melting or solidification. Oxidation of the surface of liquid solder will hinder the combination of interface atoms to achieve the required atomic spacing, thus affecting its wetting, flowing, filling and spreading ability. The capillary action of liquid solder wetting on the base metal will determine the binding ability of solder and base metal, at the same time, it affects the filling ability; the spreading or diffusion of liquid solder on the surface of the base metal affects the filling ability on the one hand, and the separation ability of solder between dense solder joints on the other hand; when there is a certain degree of dissolution and diffusion of atoms in the interface, it is beneficial to wetting and spreading, but too much mutual solubility or diffusion will produce too many intermetallic compounds at the interface, which is detrimental to wetting and spreading; at a certain brazing temperature, the lower the melting point of the solder, the smaller the difference between the solid and liquidus temperatures, the better the wettability and fluidity. Therefore, the solder process performance contains a wide range of content, these properties must be dialectical comprehensive analysis, can not only emphasize a certain performance and ignore the impact on other properties. From the point of view of use, according to the behavior of solder in the brazing process, the process performance and influencing factors of electronic solder are analyzed and summarized as follows: (1) Melting/curing temperature That is, the solidus and liquidus temperatures of the solder alloy and the temperature difference between the two. In the thermal cycle of brazing, in the heating stage, the solidus is the temperature at which the solder starts to melt, and the temperature at which the liquid solder starts to produce interfacial action on the solid base metal, while the liquidus is the melting end temperature; in the cooling stage, the liquidus is the starting temperature at which the solder solidifies, and the solidus is the end temperature at which the liquid solder stops the interfacial reaction. The solder is pasty between the solid and liquidus lines. The smaller the temperature difference between the solid and liquidus lines, the faster the melting or solidification speed, and the more favorable the brazing operation [71. The melting temperature of the solder is determined by the alloy composition. Electronic solders generally use tin-based alloys. When a low-melting-point metal component is added to tin, its melting temperature will decrease, while a high-melting-point metal will generally increase its melting temperature. The closer the composition of the alloy is to the eutectic point, the lower the melting temperature, and the smaller the temperature difference between the solid and liquidus. When the solder composition reaches the eutectic point, the melting temperature is the lowest, and the temperature difference between the solid and liquidus is zero.
The process performance of solder refers to its performance during use. According to the investigation, the technical problems encountered in the process of electronic soldering are mainly the behavior of liquid solder. The wetting, flow, filling and spreading of liquid solder on the surface of solid base metal are the premise of brazing. Without this premise, even if the physical, mechanical properties and microstructure of the solder are better, it is futile. In the process from melting to solidification and crystallization, the various properties of the solder are interrelated and influenced.
For example, the melting temperature of solder determines the temperature range of brazing, and the difference between the solid and liquidus temperatures of solder determines the speed of melting or solidification. Oxidation of the surface of liquid solder will hinder the combination of interface atoms to achieve the required atomic spacing, thus affecting its wetting, flowing, filling and spreading ability. The capillary action of liquid solder wetting on the base metal will determine the binding ability of solder and base metal, at the same time, it affects the filling ability; the spreading or diffusion of liquid solder on the surface of the base metal affects the filling ability on the one hand, and the separation ability of solder between dense solder joints on the other hand; when there is a certain degree of dissolution and diffusion of atoms in the interface, it is beneficial to wetting and spreading, but too much mutual solubility or diffusion will produce too many intermetallic compounds at the interface, which is detrimental to wetting and spreading; at a certain brazing temperature, the lower the melting point of the solder, the smaller the difference between the solid and liquidus temperatures, the better the wettability and fluidity.
Therefore, the solder process performance contains a wide range of content, these properties must be dialectical comprehensive analysis, can not only emphasize a certain performance and ignore the impact on other properties. From the point of view of use, according to the behavior of solder in the brazing process, the process performance and influencing factors of electronic solder are analyzed and summarized as follows:
(1) Melting/curing temperature
That is, the solidus and liquidus temperatures of the solder alloy and the temperature difference between the two. In the thermal cycle of brazing, in the heating stage, the solidus is the temperature at which the solder starts to melt, and the temperature at which the liquid solder starts to produce interfacial action on the solid base metal, while the liquidus is the melting end temperature; in the cooling stage, the liquidus is the starting temperature at which the solder solidifies, and the solidus is the end temperature at which the liquid solder stops the interfacial reaction. The solder is pasty between the solid and liquidus lines. The smaller the temperature difference between the solid and liquidus lines, the faster the melting or solidification speed, and the more favorable the brazing operation [71. The melting temperature of the solder is determined by the alloy composition. Electronic solders generally use tin-based alloys. When a low-melting-point metal component is added to tin, its melting temperature will decrease, while a high-melting-point metal will generally increase its melting temperature. The closer the composition of the alloy is to the eutectic point, the lower the melting temperature, and the smaller the temperature difference between the solid and liquidus. When the solder composition reaches the eutectic point, the melting temperature is the lowest, and the temperature difference between the solid and liquidus is zero.
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