In PCB manufacturing, the stripping process is a crucial step in removing anti-corrosion ink (dry film or wet film), and its quality directly affects the subsequent etching or electroplating effect. The following are the precautions and key points of the film stripping process:
First, selection and control of the stripping solution
Type of stripping solution
Alkaline stripping solution: Suitable for most dry and wet membranes, sodium hydroxide (NaOH) or potassium hydroxide (KOH) solutions are commonly used, with a concentration typically ranging from 2% to 5%.
Organic solvent film stripping solution: It is used for special inks or insoluble dry films, but it is costly and has poor environmental friendliness.
Note: Select the film removal solution according to the type of ink to avoid incomplete film removal or damage to the substrate due to mixed use.
Concentration and temperature of the stripping solution
Concentration: It must be strictly controlled within the specified range (such as 3%±0.5%). If it is too high, it will corrode the copper foil; if it is too low, the film will not be removed completely.
Temperature: Usually 40-60℃. If the temperature is too high, it will accelerate the evaporation of the stripping solution, resulting in a change in concentration. If the temperature is too low, the demolding speed will be slow.
Monitoring: Regularly test the concentration and temperature of the stripping solution, and replenish or replace it in a timely manner.
Second, film removal equipment and operation
Spray pressure and uniformity
Pressure: The spray pressure should be moderate (such as 1-2kg/cm²). If the pressure is too high, it may damage the circuit; if it is too low, the film will not be removed thoroughly.
Uniformity: Ensure full coverage of the spray to avoid local film peeling and residue.
Control of demolding time
Adjust the film removal time according to the ink thickness and type (usually 1 to 3 minutes). If the time is too short, the ink will remain; if it is too long, the copper foil may be corroded.
Regularly check the film removal effect and optimize the time parameters.
Equipment maintenance
Regularly clean the nozzles and pipes to prevent blockage.
Check the sealing of the film removal tank to prevent the evaporation or leakage of the film removal solution.
Third, post-treatment after membrane removal
Water washing and drying
After the film is removed, the PCB should be thoroughly rinsed with a high-pressure water gun to remove the residual film removal solution and ink debris.
Use hot air drying or vacuum drying to avoid water stains remaining.
Quality inspection
Visual inspection: Confirm that there is no ink residue on the surface of the circuit and that the copper foil is not corroded or scratched.
AOI inspection: Use automatic optical inspection equipment (AOI) to check the accuracy and integrity of the lines.
Environmental protection treatment
The waste liquid from membrane stripping needs to be treated centrally to comply with environmental protection regulations (such as neutralizing pH value and removing heavy metal ions).
Avoid direct discharge to prevent environmental pollution.
Fourth, Common Problems and Solutions
The stripping film is not clean
Reasons: Low concentration of the stripping solution, low temperature, short time or uneven spraying.
Solution: Adjust the parameters, increase the concentration or temperature of the stripping solution, and extend the stripping time.
Corrosion of copper foil
Reasons: The concentration of the stripping solution is too high, the temperature is too high, or the stripping time is too long.
Solution: Reduce the concentration or temperature and shorten the stripping time.
Ink residue causes a short circuit
Reason: Incomplete film removal or incomplete water washing.
Solution: Strengthen the film stripping and water washing processes, and increase AOI inspection.
Fifth, suggestions for process optimization
Parameter standardization
Formulate a detailed stripping process parameter table, including the type, concentration, temperature, time and spray pressure of the stripping solution.
Personnel training
Operators need to be familiar with the film stripping process flow and equipment operation, and receive regular skills training.
Continuous improvement
Through experiments and data analysis, optimize the stripping film process parameters to improve production efficiency and product quality.
Summary
The stripping process is an indispensable step in PCB manufacturing, and its quality directly affects the yield and reliability of PCBS. By strictly controlling the selection and concentration of the film removal solution, equipment operation, post-treatment and environmental protection measures, problems such as incomplete film removal and copper foil corrosion can be effectively avoided, ensuring the accuracy and integrity of PCB circuits. Meanwhile, continuously optimizing process parameters and strengthening personnel training are the keys to improving the level of film stripping process.
