The PCB loaded onto a linear conveyor undergoes different operations, namely, fluxing, preheating and wave soldering. The conveyor is usually set at an angle of about 7º to 10º to the horizontal to enable excess molten solder to drain out from the board into the solder tray. For fluxing, a foamed standing wave or spraying is commonly used.
The next stage is preheating the PCB. Preheating is done to evaporate the flux solvent, activate the flux, and reduce thermal shock to the board when it touches the solder wave. Hot-air blowers or infrared heaters are commonly used.
Solder is heated in the solder bath bed in the wave soldering stage. A solder wave is generated by continuously pumping molten solder in the reservoir. The wave thus formed is a standing wave with a dross-free, clean surface. The wave soldering machine can be set to adjust the shape and height of the wave. The assembled PCB, after fluxing and preheating, is passed over the solder wave. All solder points, which are in direct contact with the solder wave, establish perfect soldering.
Surface-mount soldering
The PCB is the heart of an electronics assembly. The quest for reliability and high efficiency in minimal space has led to the introduction of surface-mounted devices. Smaller components and higher packaging densities, with marked savings in size, weight and high-speed automated assembly, are the main advantages of surface-mount technology. This technology is widely used in pocket calculators, computers, communication field (especially in satellite communication), consumer electronics and automotive industry.
In this type of assembly, all the components are assembled on the same side. Solder paste is applied on the pads. The surface-mount components are then placed on the paste. Heat is applied to make the paste melt and flow, forming joints. Solder paste plays an important role in the assembly of surface-mount devices. The flux content of solder pastes makes the track surface clean, allowing perfect joints.
The author is ex-Manager (R&D), UMS Radio Factory, Coimbatore and former general manager, Sulax Corporation, Bengaluru
