Wave soldering is a highly automated mass soldering technology primarily used to reliably connect the leads of through-hole technology (THT) components to a printed circuit board (PCB), and it remains a cornerstone of PCBA manufacturing for high-volume production. The process works by briefly contacting the bottom of the flux-coated and preheated PCB with a wave of molten solder, completing the formation of all THT solder joints in a very short time, ensuring the mechanical strength and electrical continuity of components. The wave soldering machine consists of four core functional areas: fluxing, preheating, soldering, and cooling, each of which plays a critical role in determining the quality of the final solder joints.

The fluxing stage is the first step in the wave soldering process, where flux is uniformly applied to the bottom of the PCB via spraying or foaming. Flux is a key chemical medium that removes oxides from the metal surfaces of the PCB pads and component leads, preventing re-oxidation during preheating and soldering, and promoting the wetting of the solder. The preheating stage follows, whose purpose is to activate the flux, evaporate any moisture present on the PCB, and mitigate thermal shock when the PCB comes into contact with the molten solder. Proper preheating is essential to avoid defects such as cold solder joints and PCB delamination, as sudden temperature changes can cause the PCB to warp or components to crack.

The soldering stage is the core of the process, where the PCB is conveyed over a wave of molten solder (typically an alloy of tin, silver, and copper for lead-free applications) at a controlled temperature (usually between 250°C and 260°C). To address the increasing pin density and assembly complexity in modern PCB designs, contemporary wave soldering machines often use a dual-wave system. The dual-wave system includes a turbulent wave (pre-solder wave) that overcomes surface tension in densely packed pin areas, ensuring solder penetrates tight spaces, and a laminar wave that provides a smooth separation between the PCB and solder, clearing excess solder and preventing defects like bridging and icicles. The final stage is cooling, where the soldered PCB is cooled rapidly to solidify the solder joints, ensuring their stability and strength. Proper control of each stage’s parameters, including flux application rate, preheating temperature, solder wave height, and cooling rate, is critical to achieving consistent, high-quality solder joints and minimizing defects.