The flux is sprayed on the PCB board. There is a lot of yellow on the solder joint. Which is the reason for the flux?
There may be problems in the spraying process, or it may be the quality of the soldering flux. This is also an experiment to do the analysis of defective products
Flux impure, containing impurities or flux, of poor quality.
LZ, I suggest you let the supplier re debug, see it, make some improvements in the preparation
