Detailed explanation of selective welding technology for PCB circuit board

Date：2022-06-13 15:37:29Views：779

With the development of electronic technology, surface mount components are more small and diversified, through-hole plug-in components are gradually reduced, and it is more and more difficult to weld through-hole components (such as components with large heat capacity or small spacing), especially for products with high reliability requirements. Selective welding is a new welding method. Compared with wave soldering, the most obvious difference between them is that the lower part of PCB is completely immersed in liquid solder in wave soldering, while in selective welding, only some specific areas are in contact with solder wave. Then, what are the process flows of PCB selective welding?

The process flow of selective welding includes: flux spraying, PCB preheating, immersion welding and drag welding.

1. Flux coating

In selective welding, the flux coating process plays an important role. At the end of welding heating and welding, the flux shall have sufficient activity to prevent bridging and PCB oxidation. The x/y manipulator carries the PCB through the upper part of the flux nozzle, and the flux is sprayed on the position of the PCB to be welded. The flux has many ways, such as single nozzle spray, microporous spray, synchronous multipoint / graphic spray.

2. PCB preheating

The main purpose of preheating is not to reduce the thermal stress, but to remove the solvent pre drying flux and make the flux have the correct viscosity before entering the solder wave. During welding, PCB material thickness, device package specification and flux type determine the setting of preheating temperature.

3. Welding process

There are two kinds of selective welding processes: drag welding process and immersion welding process.

(1) Drag welding process

The drag soldering process is completed on the solder wave of a single small nozzle, which is suitable for welding in a very tight space on PCB. PCB moves on the solder wave of the welding nozzle at different speeds and angles to achieve the best welding quality. After the flow direction of solder solution is determined, the welding nozzle is installed and optimized in different directions for different welding needs; The manipulator can approach the soldering wave from different directions, i.e. from 0 ° to 12 °, so users can solder various devices on electronic components.

Compared with the immersion welding process, the solder solution of the drag welding process and the movement of PCB board make the heat conversion efficiency during welding better than the immersion welding process. There are also shortcomings in the single nozzle solder wave drag welding process: the welding time is the longest among the three processes of flux spraying, preheating and welding.

(2) Immersion welding process

The immersion welding process system has multiple solder nozzles and is designed one-to-one with the PCB to be welded. Although it is less flexible than the manipulator type, its output is equivalent to the traditional wave soldering equipment, and the equipment cost is lower than the manipulator type. According to the size of PCB, single board or multi board parallel transmission can be carried out. All solder joints to be welded will complete flux spraying, preheating and welding in parallel at the same time.

The above is the PCB selective welding process. I hope it can help you!