What are the common defects in PCBA processing?

1. Short circuit

Refers to the phenomenon that two independent adjacent solder joints are connected after soldering. The reasons for this are too close distance between solder joints, improper arrangement of parts, incorrect soldering direction, too fast soldering speed, insufficient flux coating, poor solderability of parts, poor solder paste coating, too much solder paste, etc.

2. Empty soldering

The tin ditch is not tinned, and the parts and substrate are not soldered together. The reasons for this situation are unclean solder ditch, high feet, poor solderability of parts, extravagant parts, improper glue dispensing, and glue overflow on the solder ditch, which will cause empty soldering. The PAD of the empty soldered parts is mostly bright and smooth.

3. False soldering

There is tin between the part foot and the solder ditch, but it is not actually completely connected by the tin. Most of the reasons are that the solder joint contains rosin or caused.

4. Cold soldering

Also known as undissolved tin, caused by insufficient soldering temperature or too short soldering time. This defect can be improved by secondary soldering. The surface of the solder paste at the cold solder joint is dark and mostly powdery.

5. Parts falling off

After soldering, the parts are not in the proper position. The reasons for this are improper glue selection or dispensing, incomplete glue maturation, too high solder wave and too slow soldering speed.

6. Missing parts

Parts that should be installed are not installed.

7. Damage

The appearance of the parts is obviously incomplete, caused by material defects, or process damage, or cracks in the parts during the soldering process. Insufficient preheating of parts and substrates, too fast cooling speed after soldering, etc., all tend to promote the breakage of parts.

8. Stripping

This phenomenon often occurs on passive parts. It is due to the poor plating treatment of the end part of the part. Therefore, when passing through the tin wave, the plating dissolves into the tin bath, causing the structure of the end to be destroyed and the solder adhesion to be poor. Higher temperature and longer soldering time will make the stripping of bad parts more serious. In addition, the general flow soldering temperature is lower than wave soldering, but the time is longer. Therefore, if the parts are not good, stripping often occurs. In addition to changing the parts, appropriately controlling the flow soldering temperature and time, you can also choose a solder paste containing silver components to inhibit the dissolution of the end of the parts. It is much more convenient to operate than changing the solder component of wave soldering.

9. Tin tip

The surface of the solder joint does not present a smooth continuous surface, but has sharp protrusions. The possible causes are too fast soldering speed, insufficient flux coating, etc.

10. Too little tin

The soldered parts or part feet have too little tin.

11. Solder balls (beads)

Spherical tin on PCB, parts, or part legs. Poor quality solder paste or long storage, improper PCB preheating, improper solder paste coating, and too long solder paste coating, preheating, and soldering process can easily cause solder balls (beads).

12. Open circuit

The circuit should be connected but is not.

13. Tombstone effect

This phenomenon is also a type of open circuit, which is easy to occur on CHIP parts. The reason for this is that during the soldering process, different tensions are generated between different solder joints of the parts, causing one end of the part to tilt up. The reason for the difference in tension at both ends is related to the difference in solder paste volume, solderability, and solder dissolution time.

14. Wick effect

This often occurs on PLCC parts. The reason for its formation is that the temperature of the part foot rises higher and faster during flow soldering, or the soldering is not good, so that the solder paste melts and rises along the part foot, resulting in insufficient solder joints. In addition, insufficient preheating or no preheating, and the solder paste is easy to flow, etc., will all promote this phenomenon.

15. CHIP parts turn white

In the SMT process, the marked surface of the part value is soldered on the PCB upside down, and the part value cannot be seen. The part value is correct and will not affect the function.

16. Reverse polarity/reverse direction

The component is not placed in the specified direction.

17. Displacement

18. Too much or insufficient glue:

19. Sideways