In order to wave soldering the circuit board of SMT components, the first process to be used is the red glue SMT process. It is to paste the red glue on the solder pad of the components, and then solidify the components on the solder pad of the circuit board after high temperature curing in the reflow oven, and then pass through the plug-in components and then pass through the wave soldering machine for wave soldering together with the plug-in components. Guangshengde technology is introduced in detail below.

If the wave soldering of SMD circuit board must adopt double wave soldering process.

The double wave soldering technology is mainly used to weld the board with many and dense components, especially the circuit board with patch components on the welding surface. The double wave soldering machine has two solder waves, the first one is turbulent wave, and the second one is smooth wave. During welding, the components pass through turbulent waves. The turbulent wave is ejected from a long and narrow gap, and a certain pressure and velocity impact the welding surface of PCBs and enter into the narrow and dense welding areas of components.

Due to a certain impact pressure, the turbulent wave can penetrate into the dense welding area which is difficult to enter, which is helpful to overcome the welding dead zone formed by exhaust and shielding, and improve the ability of solder to reach the dead zone. However, the impact speed of turbulence wave is fast and the action time is short, so the heating of welding area and the wetting expansion of solder are not uniform and sufficient, and the solder joints may be bridged or adhered with excessive solder, so the second wave is needed. The main purpose of the conveyor belt is to send the circuit board to the wave soldering machine. Along the way, it passes through the flux adding area, preheating area, wave soldering furnace, etc.

Common problems in wave soldering of SMD circuit board

The wave soldering of the circuit board of SMD components is to use the wave soldering machine after the components are cured by the red glue process. In this way, the common wave soldering problems are empty soldering, tin bonding and dropping parts. The specific solutions are explained below.

1. Wave soldering and empty soldering of SMD circuit board

Most of the reasons for the empty soldering in the wave soldering of SMD PCB are that the component is too dense, the flux is not sprayed on the pad, the flux quality is not up to standard, or there are pollutants on the pad, such as red glue polluting the component pad, and the molten tin can not be welded with the pad. Another possible reason is that the shock wave of the wave soldering furnace can't impact the pad because of the too dense component feet, or cause the wave soldering machine to weld the patch components empty. To solve this problem, we should find out the reasons from these aspects and then solve them.

2. The problem of solder joint in wave soldering of SMD circuit board is analyzed and solved from the following four aspects

a. Design according to PCB design specification. The long axis of the two end chips should be perpendicular to the welding direction, and the long axis of SOT and SOP should be parallel to the welding direction. Widen the pad of the second pin after SOP (design a solder pad);

b. According to the PCB size, whether the multi-layer board, the number of components, there are mounting components, set the preheating temperature;

c. The tin wave temperature is 250 ℃ ± 5 ℃, welding time 3 ~ 5S. When the temperature is slightly lower, the belt speed should be slowed down;

d. It may be a flux problem. Change the flux.

3. Analysis and solution to the problem of missing parts in wave soldering of SMD circuit board

If the problem is serious, check whether the temperature and time of reflux furnace are consistent with the red glue parameters you use. If you look at the place where the glue is applied, whether the ink is dropped or the red glue is on the board, only the components are dropped. If it is the former, it may have something to do with your circuit board. If it is the consequence, it may be that the heat resistance of red glue is not very good, which needs to be discussed with the supplier. Generally speaking: the wave soldering temperature is too high or the tin wave is uneven will cause the impact on the red glue, resulting in the drop of parts. To solve the problem of wave soldering chip components drop, find out the reason from the above analysis.