The principle of infrared hot air reflow soldering

In order to avoid the defects of infrared radiation heating in reflow soldering, mainstream reflow soldering equipment has introduced necessary circulating hot air, using forced convection of hot air to improve the uniformity of heating. In recent years, some equipment manufacturers have developed reflow equipment (high-temperature motors) that directly uses hot air heating.

Hot air convection uses pre heated hot air or nitrogen (which can avoid oxidation at high temperatures) as the heat source, and uses its circulating convection to heat the welding area. The temperature of the hot air is set near the welding temperature, and the speed of convection and the humidity of the hot air determine the speed of heating. Hot air convection gradually transfers heat from the surface to the interior of an object for heating. Its heating and cooling curves are relatively gentle and stable, which can reduce the thermal shock caused by excessive temperature rise rates. However, preheating and welding times are relatively long, and considering that chip components are getting smaller, excessive wind force may cause displacement of the components. Therefore, in addition to controlling the wind direction and speed, infrared radiation and hot air convection are commonly used in industry for heating. The circulating hot air can not only dissipate heat from overheated components, but also quickly supplement heat to components or welding parts with high heat demand, making the heating process of components of different sizes and heat capacities on PCBs more uniform. Balance, take the length of both.

There are various forms of infrared hot air reflow soldering, and the main difference is reflected in the heating method of the equipment. However, due to the different heating methods, the influencing factors and process parameters that need to be controlled also vary. According to the main heating methods, this type of reflow soldering is mainly divided into three types: infrared reflow soldering, infrared hot air reflow soldering, and hot air cycle reflow soldering. In infrared reflow soldering, infrared radiation is the main heating method, and over 80% of the heat in the soldered area is generated by thermal radiation; In infrared hot air reflow soldering, the heat generated by thermal radiation and hot air convection account for about 40% and 60% respectively. In hot air circulation reflow soldering, more than 80% of the heat in the soldered area is caused by hot air convection.