source:Other information release time:2023-03-25 Hits: Popular:PCB Assembly company
The development process of the industrial process of PCB circuit board, a obvious trend return welding technology. In principle, traditional plug -in parts can also be used for reflux welding. Its advantage is that it is possible to complete all the solder joints in the same time to minimize production costs. However, temperature -sensitive elements restrict the application of reflux welding, whether it is installation or SMD. Then people turn their eyes to choose welding. Most applications can be selected to choose welding after reflux welding. This will become economical and effectively complete the welding method of the remaining plug -in parts, and it is completely compatible with future lead -free welding.
Selective welding process characteristics
You can understand the characteristics of selective welding by comparison with the peak welding. The most obvious difference between the two is that the lower part of the PCB in the peak welding is completely immersed in liquid solder, and in selective welding, only some specific areas are in contact with weld waves. Because PCB itself is a bad thermal conductivity, it does not heat the melt -melting neighboring component and PCB area welding joints during welding. Before welding, you must also apply the welding pre -welding. Compared with wave welding, the welded agent only coated at the lower part of the welding part of the lower part of the PCB, not the entire PCB. In addition, selective welding is only suitable for welding of inserted elements. Selective welding is a new method that thoroughly understands that selective welding processes and equipment are necessary for successful welding.
Selective welding process
Typical selective welding processes include: sprinkler spray, PCB preheat, soaked and mop welding.
Welding coating process
In selective welding, the coating process of the welded agent plays an important role. At the end of welding heating and welding, the welded agent should have sufficient activity to prevent bridges from generating and prevent PCB from oxidizing. The welding spray was carried by the X/Y robotic hand to carry the PCB above the top of the welded nozzle, and the welded agent was sprayed on the PCB to the welding position. The welds have a single -mouth spray type, microporous jet type, synchronous multi -point/graphic spray. The microwave peak selected welding after the return welding process is the most important thing is to accurately spray the welds. Micro -hole jet type will definitely not stain the area outside the welding joint. The diameter of the minimum welding point of the micro -point spray is greater than 2mm, so the location accuracy of the welding deployed on the PCB is ± 0.5mm to ensure that the solder is always covered on the welded area. The amount of welded doses is generally recommended for 100%safety tolerance range.
The main purpose of the preheating in selective welding process is not to reduce thermal stress, but to remove solvents pre -drying welds. Before entering the welding wave, the solder has the correct viscosity. When welding, the effect of the heat in the preheating on the welding quality is not a key factor. The thickness of the PCB material, the equipment packaging specifications and the type of welding agent determine the preheating temperature. In selective welding, there is a different theoretical explanation of preheating: Some process engineers believe that PCB should be preheated before the welding agent is sprayed; another point of view is that the welding does not need to be preheated and directly welded. Users can arrange selective welding processes based on specific conditions.
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