Common problems in SMT chip processing?

Common problems in SMT chip processing?

Common problems of solder beads in SMT chip processing and welding technology: insufficient preheating of PCB during reflow soldering; The setting of reflow temperature curve is unfair, and there is a large gap between the plate surface temperature before entering the welding area and the welding area temperature; When the solder paste is taken out from the cold storage, it can not completely return to room temperature; The solder paste is exposed to the air for a long time after opening; Tin powder splashes on the PCB surface during chip placement; In the process of printing or transfer, there is oil or water sticking to the PCB; The distribution of flux in solder paste is unfair, including solvent or liquid additive or activator that is not easy to evaporate.

The above first and second reasons can also explain why the newly replaced solder paste is prone to such doubts. The main reason is that the current temperature curve does not match the solder paste used.

The third, fourth and sixth reasons can be formed by improper manipulation by users; The fifth reason may be that the solder paste has no viscosity or too low viscosity due to improper storage of the solder paste or failure of the solder paste beyond the shelf life, resulting in splashing of tin powder during patch; The seventh reason is formed by the solder paste supplier's own production technology.

There are many residues on the board surface after SMT patch welding: there are many residues on the PCB board surface after welding, which is also a question often reflected by customers. The existence of many residues on the board surface not only affects the brightness of the board surface, but also has a certain impact on the electrical properties of the PCB itself; The main reasons for the formation of more residues are as follows: when promoting solder paste, we do not know the plate conditions and needs of customers, or the selection fault caused by other reasons; The content of rosin resin in solder paste is too much or its quality is not good.