6-10 FQA
1. Flux doesnot contact with the bottom surface well; the angle between bottom and solder is improper.
2. Flux ratio is improper.
3. Speed of belt conveyer is improper; The standard speed should be in the range of  1.2-1.8m/min. If speed of belt conveyer is too fast, soldering joints could be bright and needle-shaped; If it’s too slow, soldering joints could be roundish and stubbed.
4. Too much or metamorphic anti-oxidantion oil in the soldering fumace.
 5. Improper preheating temperature. The standard temperature before soldering should be in the range of 75-100 ℃ (according to different situations)
 6. Improper preheating temperature. The standard temperature is in the range of 245-255℃. If the temperature is too high, soldering joints could be bright and needle-shaped; If it’s too slow, soldering joints could be roundish and stubbed.
7. The wave of soldering furnace is unstable.
8. There are impurities in solder in the soldering furnace.
9. Improper direction and array of base pin of components.
10. Wrong treatment with PCB and leading wire.

Chart of Common Soldering Joints Problems