Wave soldering is a kind of solder wave that forms a specific shape on the surface of molten liquid solder by the action of pump pressure. When the assembly with components inserted passes the solder wave at a certain angle, the solder joint is formed in the pin solder area. Process technology. In the process of being transported by the chain conveyor, the components are preheated in the preheating zone of the welding machine (the preheating of the components and the temperature to be reached are still controlled by the predetermined temperature curve). 

In actual welding, the preheating temperature of the component surface is usually controlled, so many devices have added corresponding temperature detection devices (such as infrared detectors). After preheating, the component enters the tin bath for soldering. The tin bath contains molten liquid solder, and the nozzle at the bottom of the steel bath sets a wave shape of the molten solder, so that when the component welding surface passes through the wave, it is heated by the solder wave, and at the same time, the solder wave wets the solder area and Carry out expansion filling, and finally realize the welding process.

Obviously, wave soldering uses convection heat transfer principle to heat the welding zone. The molten solder wave acts as a heat source. On the one hand, it flows to wash the lead solder area, and on the other hand, it also plays a role in heat conduction. The lead solder area is heated by this effect. When using silver-tin solder, the temperature of the molten solder is usually controlled at around 245°C. In order to ensure the temperature rise of the soldering zone, the solder wave usually has a fixed width, so that when the welding surface of the component passes the wave, there is sufficient heating, wetting and other time. In traditional wave soldering, a wave is generally used, and the wave is relatively flat. With the use of lead-free solders, the dual-wave form is currently used.

The leads of the components provide a way for the liquid solder to immerse into the metallized vias. When the pin contacts the solder wave, the liquid solder climbs up along the pin and the hole wall with the help of surface tension. The advancement of the capillary action of the metallized through holes promotes the climb of the solder. After the solder reaches the pad of the PcB part, it spreads under the action of the surface tension of the pad. The rising solder discharges the flux gas and air in the through hole, thereby filling the through hole, and finally forming a solder joint after cooling.

 The main difference between wave soldering and reflow soldering is the heating source and solder supply in soldering.

In wave soldering, the solder is pre-heated and melted in the tank. The solder wave from the pump acts as a heat source and provides solder. The melted solder wave heats the PcB vias, pads, and component leads, while also providing the solder needed to form solder joints. In reflow soldering, solder (solder paste) is pre-quantified on the soldering area of the PCB. The role of the heat source during reflow is to make the solder melt again.

A wave soldering machine is mainly composed of conveyor belt, heater, tin bath, pump, flux foaming (or spray) device, etc. Mainly divided into flux addition area, preheating area, welding area.

The solder in the tin bath is gradually melted by the heating of the heater. The molten liquid solder forms a wave of a specific shape on the liquid surface of the solder bath under the action of a mechanical pump (or electromagnetic pump). The PCB with the components inserted is placed on the conveyor and passes through the solder wave through a certain angle and a certain immersion depth to achieve solder spot welding, so it is called wave soldering. 

For a single wave, there is only one wave, called advection wave. For double waves, the first wave is called a spoiler wave, and the second wave is called an advection wave (smooth wave).

The role of turbulent waves: SMT component soldering and preventing solder leakage, it ensures proper distribution of solder through the circuit board. The solder penetrates through the slit at a relatively high speed, thereby penetrating into the narrow gap. The spraying direction is the same as the circuit board proceeding direction. For SMT components, spoiler waves can basically complete welding. But for through-hole components, the spoiler wave itself cannot properly solder the component, it leaves uneven and excess solder on the solder joint, so a second wave, the advection wave, is required.

The effect of advection wave: eliminate the burr and welding bridge caused by turbulent wave. The advection wave is actually the wave used by the single wave soldering machine. Therefore, when the traditional through-hole components are welded on the dual wave machine, the spoiler wave can be turned off, and the welding can be completed with the advection wave. The entire wave surface of the advection wave remains basically horizontal, like a mirror surface. At first glance, it seems that the tin wave is static. In fact, the solder is constantly flowing, but the wave is very stable.

Wave soldering machine solder joint formation: When the PCB enters the front of the wave surface, the substrate and the pins are heated, and before leaving the wave, the entire PCB is immersed in the solder, which is bridged by the solder, but at the moment of leaving the wave end A small amount of solder adheres to the pad due to the wetting force, and due to surface tension, there will be a small state of shrinkage centered on the lead. At this time, the wetting force between the solder and the pad is greater than the two pads The cohesion of the solder between. As a result, a full, round solder joint will be formed, and the excess solder leaving the tail of the wave will fall back into the tin bath due to gravity.