Basic working principle of wave soldering

Wave soldering is a kind of solder wave that makes the molten liquid solder surface form a specific shape of solder wave by means of pump pressure. When the assembly assembly with components inserted passes through the solder wave at a certain angle, a solder joint is formed in the pin soldering area. Process technology. When the components are conveyed by the chain conveyor, they are first 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 components enter the tin bath for soldering. The tin tank contains molten liquid solder, and the nozzle at the bottom of the steel tank sets the molten solder into a wave of a certain shape. In this way, when the soldering surface of the component passes through the wave, it is heated by the solder wave, and the solder wave also wets the soldering area. Carry out expansion filling, and finally realize the welding process.

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

The pins of the device provide a way for liquid solder to dip into the metallized through holes. When the pin contacts the solder wave, with the help of surface tension, the liquid solder climbs up along the pin and the hole wall. Advances in the capillary action of metallized vias have promoted solder climbing. After the solder reaches the pad of the PcB part, it spreads out under the action of the surface tension of the pad. The rising solder exhausts 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 method in soldering.

In wave soldering, the solder is preheated and melted in the tank lieutenant school, and the solder wave from the pump plays a dual role as a heat source and provides solder. The molten solder wave heats the through holes, pads and component pins of the PcB, and at the same time provides the required solder for the formation of solder joints. In reflow soldering, solder (solder paste) is pre-quantitatively distributed on the soldering area of the PCB, and the heat source during reflow is to remelt the solder.

The main component composition and working principle of wave soldering

A wave soldering machine is mainly composed of conveyor belt, heater, tin tank, pump, flux foaming (or spraying) device, etc. It is mainly divided into flux adding zone, preheating zone and soldering zone.

The solder in the solder bath gradually melts under the heating of the heater, and the molten liquid solder forms a solder wave of a specific shape on the liquid surface of the solder bath under the action of a mechanical pump (or an electromagnetic pump), and becomes a wave. The PCB with the components inserted is placed on the transmission device and passes through the solder wave through a certain angle and a certain immersion depth to realize solder joint soldering, 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 turbulent wave, and the second wave is called a advection wave (smooth wave).

The role of spoiler wave: SMT component soldering and prevention of missing soldering, it ensures proper distribution of solder through the circuit board. The solder penetrates through the slit at a relatively high speed, thereby penetrating into a narrow gap. The spray direction is the same as the direction of the circuit board. For SMT components, the spoiler wave can basically complete the welding. But for through-hole components, the spoiler wave itself cannot properly solder the components. It leaves unevenness and excess solder on the solder joints, so a second wave---advection wave is needed.

The role of advection waves: eliminate burrs and welding bridges caused by turbulence waves. The advection wave is actually the wave used by the single-wave soldering machine. Therefore, when the traditional through-hole components are soldered on the double-wave machine, the spoiler wave can be turned off and the advection wave can be used to complete the welding. 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, but 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 end 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 it leaves the end of the wave , A small amount of solder adheres to the pad due to the wetting force, and due to surface tension, it will shrink to a small state with the lead as the center. At this time, the wetting force between the solder and the pad is greater than the two pads The cohesion of the solder between. Therefore, a full, round solder joint will be formed, and the excess solder leaving the wave tail will fall back into the tin bath due to gravity.