Solder pad is not tin mainly in the SMT machine and other SMT equipment processing links, a board covered with all kinds of components is evolved from a PCB board. There are a lot of pads and through-holes on PCB light board. The situation that the pads are not tin is rare at present, but it is also a kind of quality problem in SMT.
A quality process problems, is bound to be caused by multiple reasons, in the actual production process, according to the relevant experience to check, one solution, find the source of the problem and solve it. According to analysis, there may be the following reasons:
1. Improper storage of PCB
In general, tin spraying will be oxidized in a week, OSP surface treatment can be saved for 3 months, and the gold plate can be saved for a long time (currently this kind of PCB manufacturing process is the majority)
2. Improper operation
The welding method is not correct, heating power is not enough, temperature is not enough, reflux time is not enough and so on.
3. PCB design issues
The connection of pads to copper skin will result in inadequate heating of pads.
4. Flux problem
The flux activity is not enough, the oxidized substance is not removed at the welding position of PCB pad and electronic component, and the flux at the welding position is not enough, resulting in poor wettability. The tin powder in the flux is not fully stirred and cannot be fully fused with the flux (the temperature return time of solder paste is short).
5. The PCB is faulty
PCB board is not oxidized before leaving the factory
6. Reflow oven machine problems
The preheating time is too short, the temperature is low, the tin has not melted, or the preheating time is too long, the temperature is too high, resulting in the failure of flux activity.
