Why is it not easy to tin on some china pcb assembly board pads? Here, Shenzhen PCBA processing factory POE Technology will give you an analysis of the possible reasons.
The first reason is: we need to consider whether it is a customer design problem, and we need to check whether there is a connection between the pad and the copper skin, which will cause the pad to be insufficiently heated.
The second reason is: whether there are customer operational problems. If the welding method is wrong, it will affect the heating power, the temperature is not enough, and the contact time is not enough.
The third reason is: the problem of improper storage.
①Under normal circumstances, the tin spray surface will be completely oxidized in about a week or even shorter
②OSP surface treatment process can be stored for about 3 months
③Long-term preservation of immersion gold plate
The fourth reason is: the problem of flux.
①Insufficient activity, unable to completely remove the oxide material on the PCB pad or SMD soldering position
②The amount of solder paste at the solder joint is not enough, and the wetting performance of the flux in the solder paste is not good
③The tin on some solder joints is not full, and the flux and tin powder may not be fully fused before using;
The fifth reason is: the problem handled by the board factory. There is oily substance on the pad that has not been removed, and the pad surface has not been oxidized before leaving the factory.
The sixth reason is: the problem of Flexible PCB reflow soldering. If the preheating time is too long or the preheating temperature is too high, the activation of the flux will be invalid; the temperature is too low or the speed is too fast, and the tin does not melt.