Functions and Working Principles of SMT Reflow Soldering Functions of SMT Reflow Soldering

1. Achieve efficient soldering of electronic components

By precisely controlling conditions such as temperature, the solder paste is melted and then solidified, building a stable electrical and mechanical connection between the component pins and the PCB pads. This lays the foundation for the normal conduction and stable operation of the circuits in electronic products. For example, numerous tiny surface-mounted components on the motherboard of a smartphone are soldered by this method.

2. Improve production efficiency and the degree of automation It fits well with large-scale and automated production models. PCB boards can pass through each temperature zone on the conveyor belt of the reflow soldering equipment in sequence according to the preset program without the need for manual intervention one by one. Compared with traditional manual soldering, the speed is greatly increased, and it can meet the production volume requirements for quickly bringing electronic products to the market. For instance, the number of PCB boards soldered in a medium-sized electronics factory has increased significantly after adopting this method.

3. Ensure stable and reliable soldering quality It can accurately regulate the key parameters of soldering, such as the temperature at different stages, the residence time in each temperature zone, and the cooling rate, etc. This ensures that each soldering operation is carried out under consistent and ideal conditions, reducing the defective rate of products and improving the reliability and durability of products. For example, in the production of computer motherboards, it can ensure the uniform quality of solder joints.

Working Principles of SMT Reflow Soldering

1. Composition and Functions of the Temperature Profile

(1) Preheating Zone: Gradually and gently raise the temperature of the PCB board and components to avoid PCB board deformation or component damage caused by thermal stress. Meanwhile, it activates the flux components in the solder paste. The temperature rises from room temperature to approximately 150 °C at a heating rate of 1 - 3 °C per second.

(2) Soaking Zone: The temperature is maintained between 150 °C and 180 °C. The flux plays its role fully in this zone, removing oxides and allowing the solder particles to be heated evenly, thus preparing for the reflow soldering.

(3)  Reflow Zone: This is the core area. The temperature rapidly climbs above the melting point of the solder in the solder paste (for common lead-free solder paste, it is about 217 °C). After the solder paste melts, it fills the gaps by relying on various forces to form solder joints.

(4)  Cooling Zone: Use air cooling, water cooling or other methods to prompt the rapid solidification of the solder joints. The cooling rate is controlled at 3 - 6 °C per second. An unreasonable cooling rate will affect the performance of the solder joints.

2. Changes in solder paste during reflow soldering

The beginning is paste, containing solder particles, flux and other components. The flux in the preheating zone is activated to remove oxides and improve wettability. The solder particles in the reflux zone melt and fill to form a connection; The liquid solder in the cooling zone solidifies and the components are fixed on the PCB board to complete welding.

With its role and reasonable working principle, SMT reflow has become a key process in the modern electronic manufacturing industry, promoting the development of high-quality and efficient production of electronic products.