1. Flux spraying system
Selective wave soldering adopts a selective flux spraying system, that is, after the flux nozzle runs to the designated position according to the programmed instructions, only the area on the circuit board that needs to be soldered is sprayed with flux (point spray and line spray are available) , The spray volume of different areas can be adjusted according to the program. Because it is selective spraying, not only the amount of flux is greatly saved compared with wave soldering, but it also avoids the pollution of non-soldering areas on the circuit board.
Because it is selective spraying, the precision of the control of the flux nozzle is very high (including the driving method of the flux nozzle), and the flux nozzle should also have an automatic calibration function. In addition, in the flux spraying system, the material selection must take into account the strong corrosiveness of non-VOC fluxes (ie water-soluble fluxes). Therefore, wherever there is a possibility of contact with flux, parts must be Can resist corrosion.
2. Preheating module
Preheating of the whole board is the key. Because the whole board preheating can effectively prevent the different positions of the circuit board from being heated unevenly and causing the circuit board to deform. Secondly, the safety and control of preheating is very important. The main function of preheating is to activate the flux. Since the activation of the flux is completed under a certain temperature range, both too high and too low temperatures are detrimental to the activation of the flux. In addition, the thermal devices on the circuit board also require a controllable preheating temperature, otherwise the thermal devices are likely to be damaged.
Experiments show that sufficient preheating can also shorten the welding time and lower the welding temperature; and in this way, the peeling of the pad and the substrate, the thermal shock to the circuit board, and the risk of melting copper are also reduced, and the reliability of the welding is naturally greatly reduced. increase.
3. Welding module
The welding module usually consists of tin cylinder, mechanical/electromagnetic pump, welding nozzle, nitrogen protection device and transmission device. Due to the action of the mechanical/electromagnetic pump, the solder in the tin tank will continue to gush out from the vertical welding nozzle, forming a stable dynamic tin wave; the nitrogen protection device can effectively prevent the welding nozzle from being blocked due to the generation of tin slag; and the transmission device The precise movement of the tin cylinder or circuit board is ensured to realize point-by-point welding.
1. The use of nitrogen. The use of nitrogen can increase the solderability of lead solder by 4 times, which is very critical to the overall improvement of the quality of lead soldering.
2. The fundamental difference between selective soldering and dip soldering. Dip soldering is to immerse the circuit board in a tin tank and rely on the surface tension of the solder to naturally climb to complete the soldering. For large heat capacity and multilayer circuit boards, it is difficult for dip soldering to meet the tin penetration requirements. The choice of soldering is different. The dynamic tin wave is punched out of the soldering nozzle, and its dynamic strength will directly affect the vertical tin penetration in the through hole; especially for lead soldering, because of its poor wettability, it needs dynamic Strong tin wave. In addition, oxides are not likely to remain on the strong flowing waves, which will also help to improve welding quality.
3. Setting of welding parameters.
For different welding points, the welding module should be able to personalize the welding time, wave height and welding position, which will give the operation engineer enough space to adjust the process, so that the welding effect of each welding point can be achieved. . Some selective welding equipment can even achieve the effect of preventing bridging by controlling the shape of the solder joints.
4. Circuit board transmission system
The key requirement of selective soldering to the circuit board transmission system is accuracy. In order to meet the accuracy requirements, the transmission system should meet the following two points:
1. The track material is anti-deformation, stable and durable;
2. Install a positioning device on the track through the flux spraying module and the welding module. The low operating cost of selective welding is an important reason why it is quickly welcomed by manufacturers.
Post time: Jul-31-2020