Introduction To Several Classifications Of Reflow Soldering

- Jul 03, 2019-

Hot air reflow soldering: The hot air reflow soldering furnace transfers heat energy through the laminar motion of hot air. The heater and the fan are used to continuously heat and circulate the air in the furnace, and the weldment is heated by the hot gas in the furnace to achieve welding. The hot-air reflow oven has the characteristics of uniform heating and stable temperature. The temperature difference between the upper and lower sides of the PCB and the temperature gradient along the length of the furnace are not easy to control, and it is not only used. Since the 1990s, with the continuous expansion of SMT applications and the miniaturization of components, equipment development manufacturers have improved the distribution of heaters, the circulation of air, and increased the temperature zone by 8, 10, enabling Progressively and precisely control the temperature distribution of each part of the furnace, which is more convenient for the ideal adjustment of the temperature curve. The reflow soldering furnace with full hot air forced convection has been continuously improved and perfected, and has become the mainstream equipment for SMT welding.

 

Gas phase reflow soldering: Vapor phase reflow soldering (VPS), also known as condensation soldering. Heating fluorocarbon (early FC-70 chlorofluorocarbon solvent), melting point about 215 ° C, boiling to produce saturated steam, there are condensation tubes above and to the left and right of the furnace, the steam is confined in the furnace, and the temperature is low to be welded When the PCB component is released, the latent heat of vaporization is released, so that the solder paste is melted and the components and pads are soldered. At the beginning of the United States, it was used for the welding of thick film integrated circuits (ICs). The heat release is not sensitive to the physical structure and geometry of the SMA, and the components can be uniformly heated to the soldering temperature. The soldering temperature is kept constant, and temperature control means is needed to satisfy The need for different temperature welding, the vapor phase of VPS is saturated vapor, low oxygen content, high thermal conversion rate, but high solvent cost, and is a typical ozone layer loss material, so the application is greatly restricted, and the society is now no longer basically Use this method of lossy environment.


The reflow oven is based on the addition of hot air to the IR furnace to make the temperature in the furnace more uniform. The heat absorbed by different materials and colors is different, that is, the Q value is different, and the temperature rise AT is also different. For example, the package of SMD or the like is black phenolic or epoxy, and the lead is white metal. When heated alone, the temperature of the lead is lower than that of the black SMD body. In addition, the hot air can make the temperature more uniform, and overcome the difference in heat absorption and shadow, the infrared + hot air reflow oven has been widely used.


Since infrared rays can cause adverse effects of shading and chromatic aberration in different parts of the high and low parts, hot air can be blown in to reconcile the chromatic aberration and assist the deficiencies at the dead corners, and the hot air is ideally used in the hot air. The speed of convective heat transfer depends on the wind speed, but excessive wind speed will cause the components to shift and promote the oxidation of the solder joint. The wind speed is controlled at 1.Om/s~1.8III/S. There are two forms of hot air generation: axial fan generation (easy to form laminar flow, which causes the temperature to be unclear) and tangential fan generation (the fan is installed outside the heater, creating panel eddy currents so that each temperature zone can be Precise control).