Avoid the defect of wave soldering

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Avoid the defect of wave soldering

With the current components becoming smaller and PCB more and more dense, the possibility of bridging and short circuit between solder joints is also increased. But there are some effective methods to solve this problem, one of which is to use the air knife technology. This is to blow a bunch of hot air or nitrogen to the melted solder joint when the PCB leaves the wave peak with a wind knife. This kind of wind knife with the same width as PCB can carry out full quality inspection on the whole PCB width, eliminate bridge connection or short circuit and reduce the operation cost. Other defects that may occur include faulty or missing solder, also known as an open circuit, which can form if the flux is not applied to the PCB. If the flux is not enough or the preheating stage is not operating correctly, it will cause poor top surface infiltration. Although the bridge or short circuit of welding can be found in the post weld test, it is necessary to know that the false welding will pass the test in the post weld quality inspection, and there will be problems in the later use. Problems in use will seriously affect the established minimum profit index, not only because of the costs incurred in site replacement, but also because customers find quality problems, which will have an impact on future sales.

In the wave soldering stage, PCB must dip into the wave crest to apply solder on the solder joint, so the height control of wave crest is a very important parameter. A closed-loop control can be attached to the wave peak to keep the height of the wave peak unchanged. A sensor is installed on the conveyor chain guide rail above the wave peak to measure the height of the wave peak relative to the PCB, and then the correct height of the tin dipping can be maintained by accelerating or reducing the speed of the tin pump. The accumulation of tin slag is harmful to wave soldering. If there is dross in the bath, the possibility of dross entering the wave crest will increase. This problem can be avoided by designing a tin pump system that draws tin from the bottom of the bath rather than from the top of the slag buildup. Using inert gas can also reduce tin slag and save cost.