There are as many as 20 processes in the PCB design and manufacturing process. Poor tin plating is really a headache. Poor tin on the circuit board may cause such things as line sand holes, broken lines, line dog teeth, open circuits, and line hole holes ; If the hole copper is thin, the hole is copper-free; if the hole copper is serious, the hole is copper-free; if the hole copper is thin, the hole is copper-free; The problem, therefore, encountering poor tin plating often means that it needs to be re-welded or even abandoned, and needs to be re-made. Therefore, in the PCB industry, it is important to understand the reasons for poor tin plating.
The occurrence of poor soldering is generally related to the cleanliness of the surface of the empty PCB board. If there is no pollution, there will be basically no soldering defects. Second, the soldering flux itself when soldering, the temperature, etc. Then the common bad solder in the printed circuit board is mainly reflected in the following points:
1. There are particle impurities on the surface of the board, or there are abrasive particles left on the circuit surface during the manufacturing process.
2. There are impurities such as grease and impurities on the surface of the board, or there may be residual silicone oil
3. There are flakes on the board surface without tin, and the plated layer on the board surface has particle impurities.
4. The high-potential plating layer is rough, and there is a phenomenon of burning the board.
5. The tin surface of the substrate or parts is oxidized and the copper surface is dull.
6. The coating on one side is complete, and the coating on the other side is poor. The edge of the low-potential hole has obvious bright edges.
7. The edge of the low potential hole has obvious bright edges, and the high potential plating is rough and burned.
8. Insufficient temperature or time is guaranteed during the soldering process, or the flux is not used correctly
9. Low-potential large-area plating is not possible, the surface of the board is slightly dark red or red, the plating is complete on one side, and the plating is poor on the other side.
The reasons for the poor soldering of the circuit board are mainly reflected in the following points:
1. The composition of the bath liquid is unbalanced, the current density is too small, and the plating time is too short.
2. There are too few anodes and uneven distribution.
3. Tin light agent is out of balance by a little or too much.
4. The anode is too long, the current density is too large, the local wire density of the pattern is too thin, and the light agent is out of adjustment.
5. There are some residual film or organic matter before plating.
6. The current density is too large and the plating solution is insufficiently filtered.
Then we have summarized the improvement and prevention plan for the bad situation of the PCB board tin:
1. Periodic laboratory analysis of the potion composition is added in time to increase the current density and extend the plating time.
2. Check the anode consumption from time to time and add the anode in a reasonable amount.
3. Analysis of Hirsch slot to adjust the content of light agent.
4. Reasonably adjust the distribution of the anode, reduce the current density in an appropriate amount, rationally design the wiring or puzzle of the board, and adjust the light agent.
5. Strengthen pre-plating treatment.
6. Reduce the current density, regularly maintain the filter system or weak electrolytic treatment.
7. Strictly control the storage time and environmental conditions of the storage process, and strictly operate the production process.
8. Use solvent to clean the sundries, if it is silicone oil, then you need to use a special cleaning solvent for scrubbing
9. Control the temperature during the PCB soldering process at 55-80 ℃ and ensure that there is sufficient warm-up time
10. Use flux correctly.