1. Reflow soldering is one of the key processes in SMT chip processing, and the quality of surface assembly is directly reflected in reflow soldering results. However, the welding quality problems in reflow welding are not entirely caused by reflow welding process, because the quality of reflow welding
Besides the direct relation with the temperature curve, it is also related to the equipment conditions of the production line of the SMT processing factory, the producibility design of PCB pad, the solderability of components, the quality of solder paste, the processing quality of PCB and the SMT processing of each process
Technical parameters, even with SMT chip processing plant operators have a close relationship.
1. Impact of components. When the welding ends or pins of components are oxidized or polluted, there will be welding defects such as bad wetting, faulty welding and void during reflow welding. The coplanarity of components is not good, which will also lead to welding defects such as faulty welding.
Second, the influence of PCB. SMT chip quality has a direct and very important relationship with PCB pad design. If the PCB pad is designed correctly, a small amount of heavy skew can be caused by the surface tension of the melted solder during reflow soldering
On the contrary, if the PCB pad design is not correct, even if the mounting position is very accurate, there will be welding defects such as component position deviation and monument after reflow soldering; SMT patch quality and PCB pad quality
There is also a certain relationship, PCB pad oxidation or pollution, PCB pad damp, etc., reflow soldering will produce poor wetting, false soldering, solder ball, void and other welding defects.
Third, the influence of solder paste. The content of metal powder in solder paste, oxygen content, viscosity, thixotropy and printability of metal powder have certain requirements. If the metal powder content of solder paste is high, the metal powder will evaporate with the solvent when refluxing and heating up
If the oxygen content of the metal powder is high, the splashing will be intensified and solder balls will be formed, which will also cause defects such as non wetting. In addition, if the solder paste salinity is too low or the thixotropy of the solder paste is not good, the solder paste pattern after printing
Welding defects such as solder ball bridging will be formed during reflow welding. If the printability of the solder paste is not good, the solder paste will only slide on the template when printing, in this case, the solder paste will not be printed at all.