Basic Working Principle Of Wave Soldering

Wave soldering is a method that uses pump pressure to form a specific shape of solder wave on the surface of the molten liquid solder. When the assembly with inserted components passes through the solder wave at a certain angle, solder joints are formed in the pin soldering area. Process technology. When the components are transported by the chain conveyor, they are first preheated in the preheating area of the welding machine (the component preheating and the temperature it reaches are still controlled by the predetermined temperature curve). In actual welding, it is usually necessary to control the preheating temperature of the component surface, so many equipment have added corresponding temperature detection devices (such as infrared detectors). After preheating, the components enter the tin bath for soldering. The tin bath is filled with molten liquid solder, and the nozzle at the bottom of the steel bath sets the molten solder into waves of a certain shape. In this way, when the welding surface of the component passes through the wave, it is heated by the solder wave. At the same time, the solder wave also moistens the soldering area and Expanded filling is carried out, culminating in the welding process.

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

The component leads provide a path for liquid solder to soak into the metalized through-hole. When the pin comes into contact with the solder wave, the liquid solder climbs up along the pin and hole wall with the help of surface tension. The increased capillary action of metalized vias promotes solder creep. After the solder reaches the PCB pad, it spreads out under the surface tension of the pad. The rising solder displaces flux gas and air from the via, filling the via and eventually forming a solder joint after cooling.

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

In wave soldering, the solder is preheated to a molten state in the tank, and the pumped solder wave plays the dual role of a heat source and a supply of solder. The molten solder wave heats the PCBs through holes, pads, and component pins, and also provides the required solder to form solder joints. In reflow soldering, the solder (solder paste) is pre-distributed quantitatively on the soldering area of the PCB, and the role of the heat source during reflow is to re-melt the solder.

The main components and working principle of wave soldering

A wave soldering machine mainly consists of a conveyor belt, heater, tin bath, pump, flux foaming (or spray) device, etc. It is mainly divided into flux adding area, preheating area and welding area.

The solder in the tin bath gradually melts under the heating of the heater. Under the action of a mechanical pump (or electromagnetic pump), the molten liquid solder forms a specific shape of solder wave on the liquid surface of the solder bath, becoming a wave. The PCB with inserted components is placed on the conveyor, and the solder joint is welded by passing through the solder wave at a certain angle and a certain immersion depth, so it is called wave soldering.

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

The function of the spoiler wave: welding SMT components and preventing soldering leaks. 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 spray direction is the same as the direction of the circuit board. For SMT components, spoiler waves can basically complete welding. But for through-hole components, the turbulence wave itself cannot properly solder the components. It leaves uneven and excess solder on the solder joints, so a second wave – an advection wave is needed.

The function of advection waves: eliminate burrs and solder bridges caused by turbulence waves. The advection wave is actually the wave used by a single-wave soldering machine. Therefore, when traditional through-hole components are soldered on a dual-wave machine, the turbulence wave can be turned off and the advection wave can be used to complete the soldering. The entire wave surface of an advection wave remains basically horizontal, like a mirror. At first glance, it seems that the tin wave is static. In fact, the solder is constantly flowing, but the wave is very smooth.

Wave soldering machine solder joint forming: When the PCB enters the wave front, the substrate and pins are heated, and before leaving the wave front, the entire PCB is immersed in the solder, that is, it is bridged by the solder, but at the moment of leaving the wave tail A small amount of solder adheres to the pad due to the wetting force, and due to surface tension, there will be a small shrinkage state 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 them. Therefore, a plump and 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.

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