一、Wave soldering machine
Wave solderingis a kind of solder wave with a specific shape formed on the surface of molten liquid solder by means of pump pressure. When mounted components pass through the solder wave at a fixed angle, solder joints are formed in the lead solder zone. The component is preheated in the preheating zone of the welding machine (the preheating of the component and the temperature to be reached are still controlled by the predetermined temperature curve) in the process of conveyor belt conveyor. In actual welding, the preheating temperature of the assembly surface is usually controlled, so many devices have added corresponding temperature detection devices (such as infrared detectors). After preheating, the components enter the lead slot for welding. Tin trough contains molten liquid solder. The nozzle at the bottom of the trough determines the shape of the solder. Thus, the solder wave is heated when the welding surface of the component passes through the wave. At the same time, the solder wave wets the welding zone and expands and fills the welding process.
二、Basic working principle
Wave soldering is based on the principle of convection heat transfer to the welding area heating. The molten solder wave acts as a source of heat. On the one hand, it flows to wash out the pin welding area, on the other hand, it acts as a heat conduction. The pin welding area is heated under this effect. When the silver lead solder is used, the melting solder temperature is usually controlled at about 245 degrees Celsius. In order to ensure the temperature of the welding zone, the solder wave usually has a fixed width, so that when the welding surface of the component passes through the wave, there is sufficient time for heating and wetting. In traditional wave soldering, a wave is adopted and the wave is relatively flat. With the use of lead solder, double wave mode is adopted at present.
三、The welding spot
The pin of the component provides a way to immerse the liquid solder into the metal through hole. When the pin contacts the solder wave, the liquid solder climbs up along the pin and the hole wall with the help of the surface tension. The capillary action of metallized through-hole improves the climb of solder. When the solder reaches the PcB part, the surface tension of the pad is expanded. The rising solder discharges flux gas and air from the through hole, filling the through hole and forming a solder joint after cooling.
四、What’s the difference between wave soldering and reflow oven?
The mainly different are in heating source and solder supply mode.
In wave soldering, the solder is pre-heated and melted in the trough. The solder wave pumped by the pump plays a dual role of heat source and solder supply. The solder wave of solder solder solder causes the through holes, pads and component pins of the PcB to be heated, and also provides the solder needed to form solder joints. In reflow soldering, solder paste is pre-quantitatively assigned to the solder zone of PCB. The role of heat source in reflow is to re-melt the solder.
五、Main components and working principle of wave soldering
A wave soldering machine is mainly composed of conveyor belt, heater, tin trough, pump, flux foaming (or spraying) device, etc. It is mainly divided into flux adding area, preheating zone and welding area.
The solder in the solder tank, heated by a heater, gradually melts, and the molten liquid solder, under the action of a mechanical pump (or electromagnetic pump), forms a specific shape of solder wave on the surface of the solder tank, which becomes a wave. The PCB with mounted elements is placed on the conveyor and solder joints are welded by passing through the solder wave at a certain angle and at a certain immersion depth, so it is called wave soldering.
For a single wave, there is only one wave, called the advection wave. For double waves, the first wave is called the disturbing wave, and the second wave is called the advection wave (Ping Huabo).
The role of spoiler: SMT element welding and prevent leakage welding, it ensures the proper distribution of solder through the circuit board. The solder is penetrated through the slit at a relatively high speed, thus leading to narrow gap. The direction of the jet is the same as that of the circuit board. For SMT components, the disturbance wave can basically be welded. But for through-hole components, the spoiler wave itself can not properly weld the components, it leaves the weld unevenness and excess solder, so the need for a second wave – advection wave.
The role of advection wave is to eliminate burr and weld bridge generated by the disturbance wave. 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 disturbing wave can be turned off and the soldering can be completed by advection wave. The entire wavefront of the advection wave is basically horizontal, like a mirror. At first glance, it looks as if the tin wave is static, but in fact the solder is flowing continuously, but the wave is very smooth.
六、Wave soldering machine welding spot molding
Solder Joint Forming: When PCB enters the front end of the wave, the substrate and pin are heated, and before leaving the wave, the whole PCB is immersed in the solder, that is, bridged by the solder, but at the moment of leaving the wave end, a small amount of solder is attached to the pad due to the effect of wetting force, and due to surface tension, it will come out. At present, the shrinkage of the lead wire is small, and the wetting force between the solder and the pad is greater than the cohesion of the solder between the two pads. Therefore, a full, round solder joint will be formed, leaving the excess solder at the end of the wave, and due to gravity, it will fall back into the tin bath.