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Wave soldering is a popular method for mass soldering in the manufacturing process of printed circuit boards (PCBs). The PCB is moved over a tank of molten solder, and a pump in the tank produces an upward surge of solder resembling a standing wave. When the PCB makes contact with the solder wave, the components get soldered onto the board. This method is used for both through-hole and surface mount assemblies. In the latter case, the components are initially glued onto the PCB's surface by placement machinery, before being exposed to the solder wave.

Though wave soldering has largely been replaced by reflow soldering techniques with the rise of surface mount components, it is still heavily used where surface-mount technology (SMT) isn't suitable, such as for large power devices and high pin count connectors, or in scenarios where simple through-hole technology is predominant, like in some major appliances.

The wave soldering process involves a variety of equipment, including a conveyor to move the PCB through different zones, a solder pan, a pump to create the solder wave, a flux sprayer, and a preheating pad. The solder is typically a mix of metals, with a common leaded solder being composed of 50% tin, 49.5% lead, and 0.5% antimony. However, regulations like the Restriction of Hazardous Substances Directive (RoHS) have spurred a shift towards lead-free alternatives, such as tin-silver-copper and tin-copper-nickel alloys.

The process also includes fluxing, where the goal is to clean the components to be soldered, particularly any oxide layers that may have formed. Flux can be either corrosive or noncorrosive, each with its own benefits and drawbacks. Preheating is essential to speed up the soldering process and to avoid thermal shock to the components. The quality of the soldering is dependent on the correct heating temperatures and properly treated surfaces.

Flux residues post-soldering might need to be cleaned off using solvents or deionized water. Some "no-clean" fluxes leave behind harmless residues, eliminating the need for the cleaning stage.

Different solder alloys, including combinations of tin, lead, and other metals, are used based on the required properties. A popular choice is a eutectic alloy of 63% tin and 37% lead, known for its strength, low melting range, and quick setting. Other compositions are selected for their low melting points and are helpful for soldering heat-sensitive components.

The cooling rate of the PCBs post-soldering is critical. Rapid cooling can lead to warping of the PCB and compromised solder joints, while slow cooling can make the PCB brittle and risk heat damage to some components. Hence, appropriate cooling methods, like a fine water spray or air cooling, are used.

Thermal profiling is an important step, where multiple points on a PCB are measured to determine its thermal journey through the soldering process. Tools like the Solderstar WaveShuttle and Optiminer can help production engineers to establish and control the wave solder process.

Lastly, the height of the solder wave is a crucial parameter. It is usually controlled by adjusting the pump speed on the machine. The contact time between the solder wave and the assembly being soldered is typically set between 2 and 4 seconds, and this is regulated by the conveyor speed and wave height. To get more detailed records, there are fixtures available which digitally record contact times, height, and speed. Furthermore, certain wave solder machines provide operators with an option between a smooth laminar wave or a slightly higher-pressure "dancer" wave.