Wave crest welding technology principle detailed

Wave soldering is to make the welding surface of the plug-in plate contact with high temperature liquid tin directly to achieve the purpose of welding. The high temperature liquid tin maintains an inclined surface, and the liquid tin forms a wave-like phenomenon by a special device, so it is called "wave soldering". The main material is the solder strip. The process is to insert the component into the corresponding component hole → pre-coating flux → pre-drying (temperature 90-100℃, length 1-1.2m) → wave soldering (220-240℃) → removal of excess plug-in feet → inspection. Sheng DE will introduce the detailed technical principles of wave crest welding process to you in detail.

Wave soldering production line

After the circuit board passes through a conveyor belt to the crest welder, it passes through some form of flux coating device where flux is applied to the circuit board by crest, foaming, or spraying. Since most fluxes must be reached and maintained at an activation temperature during welding to ensure full penetration of the solder joint, the circuit board passes through a preheating zone before entering the crest groove.

Lead-free wave soldering temperature curve.png

The preheating after flux coating gradually raises the temperature of the PCB and activates the flux. This process also reduces the thermal shock when the assembly enters the crest. It can also be used to vaporize any moisture that might be absorbed or to dilute the carrier solvent of the flux. If these are not removed, they will boil over the crest and cause solder sputtering, or produce steam that will remain in the solder to form hollow solder spots or sand holes.

Wave soldering structure

The length of the preheating section of the wave welding machine is determined by the yield and the speed of the conveyor belt. The higher the yield, the longer the preheating zone is needed to make the plate reach the desired infiltration temperature. In addition, dual panels and multilayer panels require higher preheating temperatures than single panels because of their larger heat capacity.

At present, wave welding machine basically uses thermal radiation to preheat. The most commonly used wave welding preheating methods include forced hot air convection, electric plate convection, electric bar heating and infrared heating. Among these methods, forced hot air convection is generally considered to be the most efficient heat transfer method for wave welders in most processes.

Wave peak welding working video

After preheating, the circuit board is welded in either single-wave (λ wave) or dual-wave (spoiler wave and λ wave) mode. For perforated components, a single wave is sufficient. When the board enters the wave crest, the solder flows in the opposite direction of the board travel, creating eddy currents around the element pins. This acts as a kind of scrub, removing all the flux and oxide film residue from the top, forming an infiltration when the solder joint reaches the infiltration temperature.

For the circuit board mixed technology assembly, the turbulent wave is generally used in front of the λ wave. The waves are narrow and disturbed with high vertical pressure, allowing solder to penetrate well between the tightly placed pins and the surface mounted element (SMD) pad. The waves are then used to shape the solder joint. Prior to any assessment of future equipment and suppliers, all technical specifications for the panels to be welded with crested surfaces need to be determined, as these can determine the performance of the machines required.

As components become smaller and PCBS become denser, the possibility of bridging and short circuit between solder joints increases. But there are some effective ways to solve this problem, one of which is the use of wind knife technology.

This is done by blowing a stream of hot air or nitrogen into the melted solder joint with an air knife as wide as the PCB as it leaves the crest. This air knife, which is as wide as the PCB, can perform a full quality check across the entire width of the PCB, eliminating bridging or short circuiting and reducing operating costs.

Other defects that can occur include weld or leak, also known as open circuit, which can form if the flux is not applied to the PCB. If the flux is insufficient or the preheating phase is not operated correctly, it will cause poor top wetting.

Although welded Bridges or short circuits can be detected during post-weld testing, be aware that faulty welds can pass the test during post-weld quality inspection and cause problems later in use. Problems in use can seriously affect the setting of minimum profit targets, not only because of the cost of on-site replacement, but also because of the quality problems identified by customers, thus affecting future sales.