Wave soldering, as a core process for through-hole mounting and mixed-assembly board soldering, directly impacts soldering quality and production efficiency through its process design. This process achieves a reliable one-time connection of through-hole component leads and some surface-mount components on the PCB through the organic combination of continuous conveying, zoned heating, and the effect of molten solder waves. In standard operating mode, the typical wave soldering process flow can be divided into four main stages: flux application, preheating, soldering, and cooling.
First is the flux application stage. Before entering the soldering area, the PCB needs to be uniformly sprayed or atomized with flux by a flux application device. The role of flux is to remove oxides from the metal surface, reduce the surface tension of the solder, improve wettability, and provide some protection during the soldering process. Modern equipment can selectively spray according to the board pattern to reduce flux usage and residue, improving subsequent cleanliness and reliability.
Then comes the preheating stage. During transport, the PCB gradually heats up through several temperature zones. Preheating activates the active ingredients in the flux, allowing them to fully exert their cleaning effect, while simultaneously reducing the temperature difference between the PCB and the solder, preventing thermal stress from causing substrate deformation or component damage. The preheating temperature and time must be precisely set based on the board thickness, component heat resistance, and flux type to ensure the substrate is in a suitable thermal state before soldering.
The third stage is soldering. The PCB is immersed in a wave generator above a molten solder bath. Driven by a pump, the solder forms a stable and continuous wave. When the bottom surface of the PCB contacts the wave, the liquid solder rises along the inner wall of the vias and wets the leads and pads, completing the electrical and mechanical connection. Wave height, soldering temperature, transport speed, and immersion time are key control parameters and need to be optimized based on materials and product structure to prevent defects such as bridging, cold solder joints, and insufficient solder.
Finally, there is the cooling stage. The soldered PCB quickly enters the cooling zone, where forced air cooling or water cooling rapidly solidifies the solder joints, forming a robust metallographic structure. Controlling the cooling rate prevents coarse solder joint grains and thermal stress concentration, improving the mechanical strength and long-term reliability of the solder joints.
Throughout the entire process, the equipment simultaneously monitors temperature, wave peak stability, and conveyor speed in real time, and uses online detection methods to promptly identify anomalies. For lead-free processes, the soldering temperature needs to be increased and the flux formulation optimized to meet environmental and performance requirements.
In summary, the wave soldering process is based on zoned temperature control, flux activation, wave immersion, and rapid cooling. Each step is closely integrated to form an efficient, stable, and repeatable soldering process, providing a reliable guarantee for the high-quality manufacturing of through-hole and mixed-assembly components.