What is PCBA gold finger get soldering?

In the smt placement process, you may encounter the phenomenon of gold finger staining, that is to say, in the printing/soldering process pcb board yellow conductive contacts stained with solder paste, thus affecting the performance of the product.

First, why the phenomenon of tin staining
1, the printing machine pressure is too large, resulting in part of the solder paste is squeezed out of the control range;
2, excessive pressure of the mounter;
3, reflow soldering preheating time is short, the heating speed is fast;
4, stencil design, the opening size is unreasonable;
5, there is pollution of equipment;

Second, how to avoid the phenomenon of tin staining

1, in terms of process:
1)adjust the appropriate squeegee pressure, wipe frequency and the spacing between the printing plate and stencil.
2)Appropriate patch pressure can reduce the tin powder is extruded.
3)Rigorous machine cleaning and maintenance can reduce the pollution index.
4)Reduce stencil opening size.
5)Slow heating rate/higher profile of homogenizing temperature.

2.In terms of materials:
1) Low splatter solder paste helps reduce gold finger tinning.
2) Use solder paste with slow wetting rate.
3) Low moisture parts and PCBs help reduce splatter.
4) Proper gold finger plating reduces exposed nickel.
Tin phenomenon, according to the site environment to analyze, find out the reasons in a timely manner, to be resolved, so as to avoid affecting the quality of PCBA products, reduce the waste of production costs.