PCB News - What are the reasons why PCB pads are not easy to be tinned?

What are the reasons why PCB pads are not easy to be tinned?

PCB factory: Everyone knows that the PCB pads are not easy to be tinned, which will affect the placement of components, which indirectly leads to the failure of subsequent tests. Here are the reasons why PCB pads are not easy to tin? I hope you can avoid these problems and minimize the loss when you make and use it.
The first reason for the PCB board pad is: we have to consider whether it is a customer design problem, 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 is a problem with the customer's operation. 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.
1. Under normal circumstances, the tin spray surface will be completely oxidized in about a week or even shorter
2. OSP surface treatment process can be stored for about 3 months
3. Long-term preservation of immersion gold plate
The fourth reason is: the problem of flux.
1. Insufficient activity, unable to completely remove the oxide material on the PCB pad or SMD soldering position
2. The 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
3. The 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 reflow soldering. If the preheating time is too long or the preheating temperature is too high, the activation of the flux will fail; the temperature is too low or the speed is too fast, and the tin does not melt.

The above is a summary of the reasons why the PCB board pads are not easy to be tinned.