The following phenomenon is a small radioactive small gray dot on the ENIG pad, as shown:
What are the reasons for this situation?
(1) Solder paste splash. In reflow soldering, if the preheating rate is too fast, it will cause the solder paste to splash. As a result, the ENIG disk/face is contaminated.
(2) The ENIG disk is contaminated with solder paste when the solder paste is printed.
(3) A device with a large-sized pin is mounted near the ENIG disk.
In response to the above situation, the countermeasures given by FASTPCBA:
(1) Reduce the heating rate of the preheating section.
(2) Increase the frequency of wiping the net and check regularly whether the bottom of the steel mesh is clean.
(3) The large heat dissipation pad steel mesh opening adopts a mesh opening.
The ENIG disk is contaminated with flux and is actually the spreading of the solder balls on the pads. If the solder paste does not splash onto the ENIG disk, it is a tin bead. Therefore, the ENIG disk solder contamination is the same as the solder ball formation.
The reason why we pay attention to the contamination of solder and flux on the ENIG disk is because the ENIG disk is generally used as a test point or keyboard. If it is contaminated, it will affect the connection rate. In fact, solder and flux splashes are a very common phenomenon, but we don't care.