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Common causes and solutions of alkaline etching in PCB board
PCB Blog
Common causes and solutions of alkaline etching in PCB board

Common causes and solutions of alkaline etching in PCB board

2021-12-30
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Author:pcb

1. Problem: The etching rate in the PCB board is reduced
Reason: due to improper control of process parameters
Solution: According to the process requirements, check and adjust the process parameters such as temperature, spray pressure, solution specific gravity, PH value and ammonium chloride content to the process specifications.

2. Problem: precipitation of etching solution in PCB board
Reason: (1) The content of ammonia is too low; (2) The water is too diluted; (3) The specific gravity of the solution is too large.
Solution:
(1) Adjust the PH value to reach the specified value of the process or appropriately reduce the exhaust air volume.
(2) Strictly follow the regulations of the process requirements or appropriately reduce the exhaust air volume when adjusting.
(3) Discharge part of the solution with high specific gravity according to the process requirements. After analysis, add an aqueous solution of ammonium chloride and ammonia to adjust the specific gravity of the etching solution to the allowable range of the process.
  

PCB board

3. Problem: The metal anti-corrosion coating in the PCB board is eroded
Reason: (1) the pH value of the etching solution is too low; (2) the chloride ion content is too high.
Solution: (1) Adjust the PH value according to the process regulations; (2) Adjust the chloride ion concentration to the process regulations.

4. Problem: The copper surface in the PCB board is black, and the etching does not move
Reason: The sodium chloride content in the etching solution is too low
Solution: Adjust the sodium chloride to the specified value of the process according to the process requirements.
  
5. Problem: There is residual copper on the surface of the substrate in the PCB board
Reason: (1) The etching time is not enough; (2) The film is not clean or there is corrosion-resistant metal.
Solution: (1) Carry out the first test according to the process requirements to determine the etching time (that is, adjust the transmission speed); (2) Check the board surface according to the process requirements before etching, requiring no residual film and no corrosion-resistant metal infiltration.

6. Problem: The etching effect on both sides of the substrate in the PCB board is obviously different
Reason:
(1) The nozzle of the etching section of the equipment is blocked;
(2) The conveying rollers in the equipment must be staggered before and after each rod, otherwise it will cause traces on the board;
(3) Water leakage in the nozzle causes the spray pressure to drop (often appearing at the joints of the nozzle and the manifold);
(4) The solution in the preparation tank is insufficient, causing the motor to run idly.
Solution:
(1) Check the blockage of the nozzle and clean it in a targeted manner;
(2) Re-examine thoroughly and arrange the staggered positions of the rollers of each section of the equipment;
(3) Check each joint of the pipeline, repair and maintain it;
(4) Observe frequently and make supplements in time to the positions specified in the process.

7. Problem: The uneven etching on the PCB board leaves some residual copper
Reason:
(1) The film removal on the substrate surface is not complete enough, and there is residual film;
(2) The thickness of the copper plating layer on the board surface is uneven when the whole board is copper-plated;
(3) When the board surface is corrected or repaired with ink, it is stained on the driving roller of the etching machine.
Solution:
(1) The film removal on the substrate surface is not complete enough, and there is residual film;
(2) The thickness of the copper plating layer on the board surface is uneven when the whole board is copper-plated;
(3) When the board surface is corrected or repaired with ink, it is stained on the driving roller of the etching machine;
(4) Check the unwinding process conditions, adjust and improve them;
(5) According to the density of the circuit pattern and the accuracy of the wire, the consistency of the thickness of the copper layer should be ensured, and the brushing and flattening process can be used;
(6) The repaired ink must be cured, and the contaminated rollers must be inspected and cleaned.
  

PCB board

8. Problem: After etching the PCB board, it is found that the wires are severely corroded.
Reason: (1) The nozzle angle is wrong, and the nozzle is out of adjustment; (2) The spray pressure is too large, causing rebound and serious side erosion
Solution: (1) Adjust the nozzle angle and nozzle to meet the technical requirements according to the instructions; (2) According to the process requirements, the spray pressure is usually set to 20-30PSIG and adjusted by the process test method

9. Problem: The substrate moving forward on the conveyor belt in the PCB board shows a phenomenon of oblique walking
Reason:
(1) The level of equipment installation is poor;
(2) The nozzles in the etching machine will automatically reciprocate left and right. It is possible that some nozzles will not swing correctly, causing uneven spray pressure on the plate surface and causing the substrate to tilt;
(3) The damage to the gear of the conveyor belt of the etching machine causes the stop of part of the transmission wheel rod;
(4) The transmission rod in the etching machine is bent or twisted;
(5) The squeezing water stop roller is damaged;
(6) The position of part of the baffle of the etching machine is too low to block the conveying board;
(7) The upper and lower spray pressure of the etching machine is not uniform, and the board will be raised when the downward pressure is too large.
Solution:
(1) Adjust according to the equipment manual, adjust the horizontal angle and arrangement of the rollers of each section, which should meet the technical requirements;
(2) Check in detail whether the swing of each section of the nozzle is correct, and adjust according to the equipment manual;
(3) Inspect section by section in accordance with process requirements, and replace damaged or damaged gears and rollers;
(4) Replace the damaged transmission rod after detailed inspection;
(5) The damaged accessories should be replaced;
(6) After inspection, the angle and height of the baffle should be adjusted according to the equipment manual;
(7) Adjust the spray pressure appropriately.

10. Problem: Copper is not completely corroded in the circuit on the PCB board, and there is residual copper on some edges
Reason:
(1) The dry film is not completely removed (it may be difficult to remove the film due to the thick and widening of the copper and tin-lead plating twice to cover a small amount of dry film);
(2) The conveyor belt speed in the etching machine is too fast;
(3) During tin-lead plating, the plating solution penetrates into the bottom of the dry film to cause a very thin dry film contaminated by the plating layer, which slows down the corrosion of copper at the place, leaving residual copper at the edge of the wire.
Solution:
(1) Check the removal of the film, strictly control the thickness of the coating to avoid extension of the coating;
(2) Adjust the conveyor belt speed of the etching machine according to the etching quality;
(3) A. Check the filming procedure, select the appropriate filming temperature and pressure, and improve the adhesion of the dry film to the copper surface. B. Check the micro-roughened state of the copper surface before filming.

11. Problem: The etching effect on both sides of the PCB board is not synchronized
Reason: (1) The thickness of the copper layer on both sides is inconsistent; (2) The upper and lower spray pressures are uneven
Solution: (1) A adjusts the upper and lower spray pressure according to the thickness of the coating on both sides (the thickness of the copper layer faces downward); B uses single-sided etching to only activate the lower nozzle pressure. (2) A. According to the quality of the etching board, check the upper and lower spray pressures and adjust them; B. Check whether the nozzle of the etching section in the etching machine is blocked, and use the test board to adjust the upper and lower spray pressures.

12. Problem: excessive crystallization of alkaline etching solution in PCB board
Reason:
When the pH value of the alkaline etching solution is lower than 80, the solubility becomes poor, resulting in the formation of copper salt precipitation and crystallization
Solution:
(1) Check whether the amount of sub-liquid in the spare tank for replenishment is sufficient.
(2) Check whether the controller, pipeline, pump, solenoid valve, etc. for sub-liquid replenishment are blocked abnormally.
(3) Check whether excessive ventilation has caused a large amount of ammonia to escape and cause the PH to drop.
(4) Check whether the function of the PH meter is normal.

13. Problem: The etching speed decreases during continuous etching in the PCB board, but the etching speed can be restored if the machine is stopped for a period of time
Reason: The ventilation volume is too low, resulting in insufficient oxygen supplementation
Solution: (1) Find out the correct amount of air extraction through the process test method; (2) Debug according to the instructions provided by the supplier to find out the correct data.

14. Problem: The photoresist comes off (dry film or ink)
Reason:
(1) The pH value of the etching solution is too high, the alkaline water-soluble dry film and the ink are easily damaged
(2) The sub-liquid replenishment system is out of control
(3) The type of photoresist itself is incorrect, and the alkali resistance is poor
Solution:
(1) Adjust according to the value determined by the process specification.
(2) Detect the PH value of the sub-liquid, maintain proper ventilation, and do not allow ammonia gas to directly enter the conveying area of the board.
(3) A good dry film can withstand PH=9 or more. B. Use the process test method to test the alkali resistance of the dry film or replace with a new photoresist brand.

15. Problem: Excessive etching of the wires in the PCB board becomes thinner
Reason:
(1) The transmission speed of the conveyor belt is too slow
(2) Side erosion will increase when PH is too high
(3) The specific gravity of the etching solution is lower than the specified value
Solution:
(1) Check the relationship between the thickness of the copper layer and the transmission speed, and set the operating parameters;
(2) Detect the pH of the etching solution, if it is higher than the range specified by the process, strengthen the ventilation until it returns to normal;
(3) Detect the specific gravity value. If it is lower than the set value, add copper salt and stop the supplement of the sub-liquid, so that the specific gravity value rises to the range specified by the process.

16. Problem: Insufficient etching in PCB board, too large residual foot
Reason:
(1) The transmission speed of the conveyor belt is too fast
(2) The pH of the etching solution is too low (its value has little effect on the etching speed, but when the pH is reduced, the side erosion will be reduced, but the residual foot will become larger)
(3) The specific gravity of the etching solution exceeds the normal value (the specific gravity has little effect on the etching speed, but when the specific gravity increases, the side etching will decrease)
(4) Insufficient etching solution temperature
(5) Insufficient spray pressure
Solution:
(1) Check the relationship between the thickness of the copper layer and the transmission speed of the etching machine, and find out the operating conditions through the process test method.
(2) Detect the pH value of the etching solution. When the value is lower than 80, it is necessary to adopt methods to increase it, such as adding ammonia or accelerating liquid supplementation and reducing the draft.
(3) A detects the specific gravity value of the etching solution, and adds more sub-liquid to reduce the specific gravity value to the specified range of the process. B Check if the sub-liquid supply system is malfunctioning.
(4) Check whether the function of the heater is abnormal.
(5) A. Check the spray pressure, and adjust it to the state of the cobweb. B Check whether the pump or pipeline is abnormal. C. The water level in the preparation tank is too low, causing the pump to run dry. Check the operating procedures of the liquid level control, replenishment, and discharge pump on PCB board.