What is the most common wave soldering preheating method?
Wave soldering means that the molten solder (lead-tin alloy) is sprayed into a solder peak of a design by an electric pump or an electromagnetic pump, or can be formed by injecting nitrogen into the solder pool, using pre-assembled components. The printed board passes the solder wave peak to achieve the mechanical and electrical connection between the solder tail of the component or the lead and the printed circuit board pad.
After the PCB board enters the wave soldering machine through the conveyor belt, it passes through a form of flux coating device where the flux is applied to the line by wave crest, foaming or spraying, since most fluxes are soldered. An activation temperature must be reached and maintained to ensure complete wetting of the solder joints, so the board must pass through a preheating zone before entering the peak slot. Preheating after flux application can gradually increase the temperature of the PCB and activate the flux, which can also reduce the thermal shock generated by the assembly entering the stain peak. It can also be used to evaporate all the moisture that may be absorbed or the carrier solvent that dilutes the flux. If these things are not removed, they will boil over the peak and cause tin sputtering, or form a vapor to remain in the solder to form a hollow. Solder joints or blisters. In addition, due to the large heat capacity of the double-panel and multi-layer, they require a higher preheating temperature than a single panel.
The current wave soldering machine basically adopts the heat radiation method for preheating. The most commonly used wave soldering preheating methods include forced hot air convection, electric heating plate convection, electric heating rod heating and infrared heating. Among these methods, forced heat convection is generally considered to be the most efficient heat transfer method for wave soldering machines in most processes. After preheating, the board is soldered with a single wave (λ wave) or a double wave (spoiler wave and lambda wave). For a perforated component, a single wave is sufficient. When the board enters the wave, the direction of solder flow is opposite to the direction of travel of the board, creating eddy currents around the component leads. This is like a washing machine that removes all of the flux and oxide film residues above and forms a wetting when the solder joint reaches the wetting temperature.
For hybrid technology assemblies, spoiler waves are also typically used before the lambda wave. This wave is narrower and has a higher vertical pressure during the disturbance, allowing the solder to penetrate well between the pin and the surface mount component (SMD) pad, and then forming the solder joint with a lambda wave. . Before making any assessments of future equipment and suppliers, it is necessary to determine all the specifications of the board to be soldered with the peaks, as these can determine the performance of the required machine.