PCB Technical - Why does continuous soldering occur during PCBA wave soldering?

Why does continuous soldering occur during PCBA wave soldering?
PCBA processing plants will have wave soldering equipment. The quality of wave soldering has a great influence on the product. Today, will analyze the solder connection problem during wave soldering. .
1. Reasons for wave soldering

1. Insufficient flux activity.

2. The wettability of the flux is not enough.

3. The amount of flux coating is too small.

4. Uneven flux coating.

5. The circuit board can't be coated with flux in regions.

6. The circuit board is not tinted regionally.

7. Some pads or solder feet are seriously oxidized.

8. The wiring of the circuit board is unreasonable (the distribution of components is unreasonable).

9. The direction of the board is wrong.

10. The tin content is not enough, or the copper exceeds the standard; [the melting point (liquid line) of the tin liquid rises due to the excessive impurity].

11. The foaming tube is clogged and the foaming is uneven, resulting in uneven coating of the flux on the circuit board.

12. The setting of the air knife is unreasonable (the flux is not evenly blown).

13. The board speed and preheating are not matched well.

14. Improper operation method when immersing tin by hand.

15. The inclination of the chain is unreasonable.

16. The wave crest is uneven.

2. Improvement measures:

1. Design in accordance with PCB design specifications. The long axis of the two end chips is perpendicular to the welding direction, and the long axis of the SOT and SOP should be parallel to the welding direction. Widen the pad of the last pin of the SOP (design a thief pad).

2. The pins of the plug-in components should be shaped according to the hole distance of the printed board and the assembly requirements. If the short-insertion welding process is adopted, the component pins of the soldering surface are exposed to the surface of the printed board by 0.8~3mm, and the component body is required when inserting. correct.

3. Set the preheating temperature according to the PCB size, whether it is a multilayer board, how many components, and where there are mounted components.

4. The tin wave temperature is 250±5 degree Celsius, and the welding time is 3~5s. When the temperature is slightly lower, the speed of the conveyor belt should be slowed down.

5. Replace the flux

The above is a related sharing of why the continuous soldering phenomenon occurs when PCBA is in wave soldering. I hope it will be helpful to everyone.
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