There are two different selective welding processes: drag welding and dip welding.
The selective towing process is performed on a single small nozzle solder wave. The drag welding process is suitable for welding in very tight Spaces on the PCB. For example, individual solder joints or pins, a single row of pins can be towed welding process. The PCB moves over the solder wave of the nozzle at different speeds and angles to achieve optimal welding quality. In order to ensure the stability of the welding process, the inner diameter of the welding nozzle is less than 6mm. After the flow direction of the solder solution is determined, the nozzle is installed and optimized in different directions for different welding needs. Manipulator can be from different directions, namely 0° ~ 12° different angles close to the solder wave, so users can be in the electronic components on the welding of a variety of devices, for most devices, the recommended tilt Angle of 10°.
Compared with the dip welding process, the heat transfer efficiency of the solder solution and PCB in the drag welding process is better than that of the dip welding process. However, the heat required to form a welding joint is transferred by the solder wave, but the mass of the solder wave is small for the single solder mouth, only the temperature of the solder wave is relatively high, can meet the requirements of the towing welding process. Example: Solder temperature 275℃ ~ 300℃, drag speed 10mm/s ~ 25mm/s is generally acceptable. Nitrogen is supplied in the welding area to prevent oxidation of solder wave, which eliminates oxidation and avoids the occurrence of bridge defects. This advantage increases the stability and reliability of the welding process.
The machine has the characteristics of high precision and high flexibility, the system of module structure design can be completely customized according to the special production requirements of customers, and can be upgraded to meet the needs of future product development. The motion radius of the manipulator can cover flux nozzles, preheating, and solder nozzles, so the same equipment can complete different welding processes. Machine – specific synchronous process can greatly shorten the cycle of the single-sided board process. Manipulator has the ability to make this selective welding with high precision and high-quality welding characteristics.
Firstly, the precise positioning capability of the manipulator is highly stable (±0.05mm), which ensures the highly repetitive and consistent production parameters of each plate.
Secondly, the five-dimensional motion of the manipulator enables the PCB to contact the tin surface at any optimized Angle and orientation to obtain the best welding quality.
Manipulator splint device installed on the tin wave height measurement needle, made of titanium alloy, under the control of the program can regularly measure the height of tin wave, by adjusting the speed of tin pump to control the height of tin wave, in order to ensure the stability of the process.
Despite all these advantages, the single-nozzle tin wave drag welding process also has a disadvantage: the welding time is the longest in flux spraying, preheating and welding. And because the welding spot is one by one, with the increase of welding spot number, the welding time will be greatly increased, and the welding efficiency is unable to compare with the traditional wave soldering process. However, this is changing and multiple nozzles can be designed to maximize yields. For example, double nozzles can be used to double yields and double nozzles can also be designed for flux.
The immersion selective welding system has a number of solder nozzles and is designed one to one with THE PCB welding spot, although less flexible than the manipulator, the output is equivalent to the traditional wave soldering equipment, the equipment cost is lower than the manipulator. Depending on the size of the PCB, single-board or multi-board parallel transmission can be carried out. All solder joints to be welded will be sprayed, preheated and welded in parallel at the same time. However, due to the different distribution of solder joints on different PCBs, special solder nozzles should be made for different PCBs. The size of the nozzle should be as large as possible to ensure the stability of the welding process without affecting the surrounding components on the PCB, which is important and difficult for the design engineer because the process stability may depend on it.
Dip selection welding process can be used to weld 0.7mm ~ 10mm solder joints. The welding process of short pins and small size pads is more stable and less likely to bridge. The distance between adjacent solder joints edges, devices, and welding nozzles should be greater than 5mm.
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