The surface quality of the copper foil is critical for the success and efficiency of the image transfer process. Prior to image transfer, the surface of the copper cylinder must be thoroughly inspected for any defects such as pits, drill scorch marks, or other unwanted areas. If any unacceptable defects are found, the transfer process should be halted immediately, and the faulty material should be discarded. Therefore, it is crucial for any printed circuit board fabrication method to clean the surface of the copper cylinder to ensure reliable usage.
In the manufacturing process of printed circuit boards, the most common issues arise from a contaminated substrate surface. To prevent this, the substrate should be shielded from oil, grease, dust, fingerprints, and harmful particles. Contamination sources can include equipment used for trimming, drilling, die cutting, or air compressor ventilation. Any contamination on the substrate surface can compromise the adhesion of the photosensitive resin or weaken the bond strength of the electroplated copper. Thus, a thorough cleaning method is essential for preparing the substrate surface.
Commonly utilized cleaning methods include:
1) Manual cleaning
– Chemical cleaning
– Degreasing (using steam or water-based substances)
2) Machine cleaning
Chemical Cleaning or Cold Cleaning:
This method involves using concentrated alkaline chemicals to eliminate oil, grease, and dirt particles from the substrate surface. The substrates are cleaned with alkaline chemicals at concentrations of 80% – 100% and temperatures ranging from 60 – 70°C for 20 – 30 minutes. After alkaline soaking, the substrates should be rinsed thoroughly with filtered, oil-free tap water and then sprayed with high-pressure water to ensure complete removal of the cleaning agent. For exposed epoxy or polyamide substrates, a neutral or acidic cleaner may be preferred over a hot alkaline solution.
The steps for chemical cleaning are as follows:
1) Immersion cleaning to remove oil
2) Water cleaning (using pressurized water above 4 bar / 60 psi)
3) Water spraying
4) Copper sink micro-etching (optional)
5) Water cleaning
6) Inspection for complete removal of oil or grease
7) Neutralization (pickling)
8) Water cleaning
Vapor Degreasing:
This method involves cleaning the substrate with condensed pure solvent vapor, typically a non-flammable solvent like CFC (trichloroethylene or perchloroethylene). The solvent vapor effectively removes grease contamination from the substrate surface. Following wiping with a clean cloth, the substrate is soaked in a solvent that acts as a stain remover without reacting chemically with the materials it dissolves. Subsequently, a pumice stone or salt-melt scrubbing is used to remove inorganic substances such as particulates and oxides and aid in oil removal. The printed circuit board is then rinsed with water and fine particles of pumice are removed with a brush.
To remove residual alkali and metal oxides and prepare a clean surface for image transfer, the board should be pickled in 10% hydrochloric acid. The final cleaning should be done with deionized water to avoid water impurities that can cause malfunctions. Drying is achieved by blowing compressed air over the substrate surface. The compressed air system should have a filter to remove grease contamination from the compressor. For thorough drying, the printed circuit board should be placed in an oven at 90°C for approximately 15 minutes.
It is important to note that solvent vapors are toxic and can be air pollutants. Operators should take precautions to avoid inhaling the vapors, ensure adequate air circulation, and prevent the vapor concentration from exceeding safe levels.
Additionally, degreasing can be carried out using foaming with a cleaning liquid, which effectively removes oil and grease without causing significant air pollution through chemical reactions with organic pollutants.
Vapor degreasing offers a more efficient cleaning process compared to cold flux cleaning by utilizing pure solvent and expedited drying. The use of ultrasonic agitation systems in vapor degreasing equipment further enhances the cleaning effectiveness through sound wave agitation.
In the manufacturing process of printed circuit boards, the most common issues arise from a contaminated substrate surface. To prevent this, the substrate should be shielded from oil, grease, dust, fingerprints, and harmful particles. Contamination sources can include equipment used for trimming, drilling, die cutting, or air compressor ventilation. Any contamination on the substrate surface can compromise the adhesion of the photosensitive resin or weaken the bond strength of the electroplated copper. Thus, a thorough cleaning method is essential for preparing the substrate surface.
Commonly utilized cleaning methods include:
1) Manual cleaning
– Chemical cleaning
– Degreasing (using steam or water-based substances)
2) Machine cleaning
Chemical Cleaning or Cold Cleaning:
This method involves using concentrated alkaline chemicals to eliminate oil, grease, and dirt particles from the substrate surface. The substrates are cleaned with alkaline chemicals at concentrations of 80% – 100% and temperatures ranging from 60 – 70°C for 20 – 30 minutes. After alkaline soaking, the substrates should be rinsed thoroughly with filtered, oil-free tap water and then sprayed with high-pressure water to ensure complete removal of the cleaning agent. For exposed epoxy or polyamide substrates, a neutral or acidic cleaner may be preferred over a hot alkaline solution.
The steps for chemical cleaning are as follows:
1) Immersion cleaning to remove oil
2) Water cleaning (using pressurized water above 4 bar / 60 psi)
3) Water spraying
4) Copper sink micro-etching (optional)
5) Water cleaning
6) Inspection for complete removal of oil or grease
7) Neutralization (pickling)
8) Water cleaning
Vapor Degreasing:
This method involves cleaning the substrate with condensed pure solvent vapor, typically a non-flammable solvent like CFC (trichloroethylene or perchloroethylene). The solvent vapor effectively removes grease contamination from the substrate surface. Following wiping with a clean cloth, the substrate is soaked in a solvent that acts as a stain remover without reacting chemically with the materials it dissolves. Subsequently, a pumice stone or salt-melt scrubbing is used to remove inorganic substances such as particulates and oxides and aid in oil removal. The printed circuit board is then rinsed with water and fine particles of pumice are removed with a brush.
To remove residual alkali and metal oxides and prepare a clean surface for image transfer, the board should be pickled in 10% hydrochloric acid. The final cleaning should be done with deionized water to avoid water impurities that can cause malfunctions. Drying is achieved by blowing compressed air over the substrate surface. The compressed air system should have a filter to remove grease contamination from the compressor. For thorough drying, the printed circuit board should be placed in an oven at 90°C for approximately 15 minutes.
It is important to note that solvent vapors are toxic and can be air pollutants. Operators should take precautions to avoid inhaling the vapors, ensure adequate air circulation, and prevent the vapor concentration from exceeding safe levels.
Additionally, degreasing can be carried out using foaming with a cleaning liquid, which effectively removes oil and grease without causing significant air pollution through chemical reactions with organic pollutants.
Vapor degreasing offers a more efficient cleaning process compared to cold flux cleaning by utilizing pure solvent and expedited drying. The use of ultrasonic agitation systems in vapor degreasing equipment further enhances the cleaning effectiveness through sound wave agitation.
