False welding: It means that the surface appears to be welded, but it is not actually welded. Sometimes the lead can be pulled out of the solder joint by hand.
Virtual soldering: only a small amount of tin soldering at the solder joint, resulting in poor contact and time-interruption. Both false welding and false welding refer to the fact that the surface of the welded parts is not fully coated with tin, and the solder between the welded parts is not fixed by tin, because the surface of the welded parts is not cleaned up or the flux is used too little.
Vacuum welding: The solder joint should be welded but not welded. Too little solder paste, parts themselves, placement of parts, placement after printing tin, etc. It will cause empty soldering.