Online PCB manufacturing virtual fake welding causes and solutions
1. Virtual fake welding means that components surface is not adequately covered with tin, and the components are not fixed with tin.This is mainly due to the fact that the weld surface is not cleaned or the flux is not used enough.Fake welding means that it appears welded, but it is not actually welded. Sometimes, it can be pulled out of the solder joint of online PCB manufacturing by move lead wires.Virtual welding refer to only a small amount solder in solder joints, resulting in poor contact signal, on and off.
2. Causes of virtual and fake welding include:
1) Oxidation or contamination of solder pads of component solder ends, pins and PCB substrates, or dampness of PCB
2)The metal electrode at the end of the passive component has poor adhesion or a single layer electrode is adopted, and the cap is taken off at the welding temperature
3) PCB design is unreasonable, and the shadow effect during wave soldering causes leakage welding.
4)PCB warping, so that PCB warping position is not contact with wave soldering well.
5)The two sides of the conveyor belt are not parallel (especially when the PCB transport frame is used), so that the PCB contact with the wave peak is not parallel.
6) The wave peak is not smooth and the height on both sides of the wave peak is not parallel. In particular, if the tin wave nozzle of the electromagnetic pump wave welder is blocked by the oxide, the wave peak will appear serrated, which is easy to cause leakage welding and virtual welding.
7) poor flux activity, resulting in poor wetting.
8)PCB preheating temperature is too high, which makes the flux carbonize and lose its activity, resulting in poor wetting of online PCB manufacturing.
3. Methods to avoid virtual and fake welding:
1) Components shall be used on a first-come-first-served basis, and shall not store in a humid environment or exceed the specified service date.Clean and dehumidification PCB.
2) Surface mount components with three-layer end structure should be selected for wave soldering. The body of components and the welding end can withstand the temperature impact of more than two times of 260℃ wave soldering
3) When SMD/SMC adopts wave soldering welding, the layout and layout direction of components should follow the principle of smaller components in front and avoiding mutual shielding as far as possible.In addition, the remaining welding pad length can be appropriately lengthened after the overlap of components in online PCB manufacturing.
4) PCB warping less than 0.8%~1.0%.
5) Adjust the transverse level of wave soldering machine and transmission belt or PCB transmission frame.
6) Clean the wave peak nozzle.
7) Replace flux.
8)Set proper preheating temperature
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