Insufficient solder joints in BGA repair can be caused by factors such as insufficient solder paste, cored solder phenomenon, damaged solder mask, and poor coplanarity of devices and PCB, but can be resolved by printing enough solder paste, avoiding damaging the solder mask, accurately aligning during solder paste printing, ensuring BGA mounting accuracy, meeting coplanarity requirements, and using microporous technology to reduce solder loss. Common problems and defects in wave soldering can be caused by factors such as improper transmission speed, low preheating and tin pot temperature, solder failure, poor solderability of component leads, and PCB layout, but can be resolved by adjusting temperature and transmission speed, testing solder content, and optimizing flux density.