What is the working principle of SMT reflow soldering?

Working principle of SMT reflow soldering oven

Abstract: Due to the development and progress of science and technology, the electronic products we are exposed to are constantly miniaturized. In the PCBA welding process, more chip components are welded. The traditional welding method can no longer meet the current industry development needs. Therefore, the reflow soldering method is adopted in the SMT chip processing process. Most of the components processed by the SMT chip are chip type, mounted transistors, ICs, etc. With the technological development of the entire SMT industry becoming more and more perfect and common, a variety of patch-processing components have emerged. As a part of SMT processing technology, the reflow soldering process technology and equipment have also been developed accordingly, and its application is becoming more and more extensive. Now it has been widely used in all electronic product fields.

What is reflow soldering?

Reflow soldering is to remelt the creamy solder pre-distributed on the circuit board PAD to realize the electrical connection between the pins of the patch processing components and the circuit board pads. Reflow soldering is the soldering of components to the PCB. Reflow soldering relies on hot air up and down convection, which melts the solder paste to form a liquid state, and performs a physical reaction under a set high-temperature airflow to achieve the effect of bonding the SMD device pins to the PCB solder end; so it is called “reflow soldering”.

The principle of reflow soldering is divided into the following descriptions: (The above figure is an example, combined with the setting of the heating temperature zone of the equipment.

Working principle of SMT reflow soldering oven

Heating zone

A. When the PCB enters the heating zone (about 60S-90S), the solvent and gas in the solder paste evaporate, and the PCB is also heated to evaporate the gas evenly. The flux in the solder paste wets the PCB pad and wets the components. The solder paste softens, covers the pad, and isolates the pad and component pins from the oxygen gas. This area is called the heating zone.

Constant temperature zone

B. When the PCB enters the constant temperature zone (about 60-120S), the PCB and components are fully preheated to prevent the PCB from suddenly entering the welding high-temperature zone, encountering violent heat, and damaging the PCB and components. This zone is called the constant temperature district.

Welding area

C. When the PCB enters the welding area (about 30-90S), the temperature rises rapidly to make the solder paste reach a molten state and form a liquid state (lead-free melting point: 217 degrees Celsius). The liquid tin moistens the PCBA pad and the component pins. Moisture and tin flow on the pins to form solder joints between tin and pins. This area is called the recirculation zone.

Cooling zone

D. The PCB enters the cooling zone (the end of the reflow zone) to cool and solidify the solder joints to form solder joints between components and pads. This area is called the cooling zone.

Summary of Working principle of SMT reflow soldering oven

The above content is shared by SZTech-SMT with you about the principle of SMT chip reflow soldering. I hope it will be helpful to you. To learn more about SMT chip processing, welcome to visit SZTech-SMT’s official website www.sztech-smt.com

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