Reflow Soldering, also known as reflow soldering, is a widely used soldering technique in the field of electronic manufacturing. The following is a detailed explanation of reflow soldering:
1、 Definition and Principle
Reflow soldering refers to a soldering method that forms solder joints by remelting pre placed solder without adding any additional solder during the soldering process. The principle is to use the circulating gas in the welding furnace to generate high temperature, which melts the solder on the circuit board with the components already attached, thereby achieving a firm connection between the components and the PCB board.
2、 Welding process and stages
The soldering process of reflow soldering is usually divided into the following stages:
Preheating zone (heating zone): This stage is used to evaporate the volatile components in the solder flux, reduce the temperature difference between different parts of the PCBA during soldering, avoid component damage caused by rapid high temperature heating, and activate the solder paste. The preheating temperature is generally set within the range of 80 to 160 ℃, and the time is about 60 to 120 seconds.
Constant temperature zone (insulation zone/active zone): This stage is used to ensure that the PCBA reaches thermal equilibrium before entering the reflow soldering stage. The temperature is usually controlled between 150 and 170 ℃, and the time is generally 23 minutes. At this stage, the volatilization in the solder paste is further removed, and the activator begins to activate, effectively removing surface oxides.
Reflow zone (reflow soldering zone): This stage is the core of the soldering process and has the highest temperature. After entering this area, SMA (Surface Mount Component) rapidly heats up and exceeds the melting point by 30-40 ℃, that is, the plate surface temperature instantly reaches 215-225 ℃. The solder paste melts quickly at this stage and quickly wets the solder pads. The time is about 5-10 seconds.
Cooling zone: This stage is used to rapidly cool and solidify the solder joints. The cooling method is usually to install a fan at the reflow soldering outlet to force cooling. The ideal cooling temperature curve should have a mirror relationship (symmetrical distribution) with the temperature rise curve in the recirculation zone.
3、 The Importance of Temperature Curve
The temperature curve of reflow soldering is one of the key factors determining the quality of soldering. By analyzing the temperature curve, the state of the components during the entire reflow soldering process can be intuitively analyzed to obtain the best solderability, avoid damage to the components due to overheating, and ensure soldering quality. Therefore, designing the reflux temperature curve appropriately can achieve high yield and reliability.
4、 Influencing factors
The quality of reflow soldering is influenced by various factors, among which the most important ones are the temperature curve inside the reflow soldering furnace and the composition of the solder paste during the electronic processing production process. In addition, the thickness of the PCB board, the size and density of components, the number of heating zones, and the length of reflow soldering can also affect the soldering quality.
