/What are the most common wave soldering preheating methods?
Nowadays, wave soldering equipment is widely used in PCBA factories, but many people still don’t know what preheating methods are used for wave soldering equipment knowledge. Then the following edition will give you a brief description of the knowledge of wave soldering to learn together!
Wave soldering refers to the flexible fibre soldering that sprays molten solder (lead-tin alloy), electric pump or electromagnetic pump into the solder peak required by the design. It can also be formed by injecting nitrogen into the solder pool. Using the solder peak of printed circuit board with pre-installed components, the mechanical and electrical connection between the solder end or pin of components and the solder disk of printed circuit board can be realized.
PCB circuit boards pass through the conveyor belt into the wave soldering machine, and then pass through some form of flux coating device, where flux is spread to the circuit by means of wave crest, foaming or spraying. Since most flux must reach and maintain an activation temperature to ensure the full wetting of solder joints during soldering, the circuit boards must pass through a preheating zone before entering the wave crest groove. Preheating after flux coating can gradually increase the temperature of PCB and activate flux, which can also reduce the thermal shock of assembly when it enters the pollution peak. It can also be used to evaporate all possible absorbed moisture or dilute flux carrier solvents, which, if not removed, boil over peaks and cause tin sputtering, or form hollow solder joints or trachoma with steam remaining in the solder. In addition, because of the large heat capacity of double panels and multi-layers, they require higher preheating temperatures than single panels.
Currently, wave soldering machines are preheated by thermal radiation. The most commonly used wave soldering preheating methods are forced hot air convection, electric heating plate convection, electric heating rod heating and infrared heating. Among these methods, forced heat convection is often considered to be the most effective heat transfer method for wave soldering machines in most processes. After preheating, the circuit board is welded by single wave (lambda wave) or double wave (disturbance wave and lambda wave). For perforated components, a single wave is enough. When the circuit board enters the wave ridge, the direction of solder flow is opposite to that of the board, which can generate eddy current around the pin of the component. It’s like a wash-up, which removes all the residues of flux and oxide film above and forms infiltration when the solder joints reach the infiltration temperature.
For mixing assembly, disturbance wave is usually used in the wavefront of lambda wave. This kind of wave is relatively narrow and has a high vertical pressure when disturbed, which can make solder penetrate well between the tightened pin and the surface mounting element (SMD) pad, and then complete the solder joint forming with lambda wave. Before making any assessment of future equipment and suppliers, it is necessary to determine all technical irregularities of plates welded with wave crests, which can determine the performance of the required machines.
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