X mm
Your position: Home >> News
Substrate surface cleaning method
The surface quality of the copper foil plays an important role in the success and throughput of the image transfer process. Care should be taken to check for pits on the surface of the copper cylinder, drill holes, and any other undesirable areas. If unacceptable defects are detected, the transfer process should be stopped and the defective material should be scrapped immediately. Therefore, any type of PCB manufacturing method should clean the surface of the copper cylinder before image transfer to facilitate reliable operation. This is a basic step. The most common problem encountered in the manufacture of printed circuit boards is due to the unclean surface of the substrate. Therefore, the substrate should be kept away from oils, grease, dust, finger prints, and harmful particles. Possible sources of contamination are equipment used for trimming, drilling, blanking, or air compressor ventilation. Any contaminants on the surface of the substrate may weaken the adhesion of the photosensitive resin or reduce the adhesion of the electroplated copper deposit. Therefore, a good cleaning method is necessary for the preparation of the substrate surface. The commonly used method is:

1) Manual cleaning

1 Chemical cleaning

2 Degreasing (steam or waterborne substances)

2) Machine cleaning

First, manual cleaning method

1 Chemical cleaning or cold cleaning

Chemical cleaning must use concentrated alkaline chemicals to remove oil, grease, and dirt particles from the surface of the substrate. Use alkaline chemicals with a concentration of 80% -100% to clean the substrate in the temperature range between 60 -70 °C. The cleaning time is 20 - 30 minutes. After alkaline soaking, the filtered, oil-free tap water should be used to effectively rinse the substrate, dip it with water, and then spray with strong water to ensure complete removal of the cleaner. Because exposed epoxy or polyamide substrates are soaked in hot alkaline solution, neutral or acidic cleaners are sometimes preferred.

Chemical cleaning steps are as follows:

1) Use a hot soak cleaner to soak and degrease;

2) Water cleaning (using 4 bar 8 or more than 60 psi of pressurized water);

3) water spray;

4) Copper sinks (optional);

5) Water cleaning;

6) Check (completely remove oil or grease);

7) Pickling (neutralization);

8) Wash with water.

2 Steam degreasing

This process involves cleaning the substrate with condensed, pure solvent vapors to bring non-flammable solvents such as chlorofluorocarbons (trichloroethylene or perchloroethylene) into its boiling point. This solvent vapor removes the surface of the substrate. Grease contaminants. Figure 7-2 shows the cleaning process with the solvent degreasing. The first step is to gently wipe with a clean cloth, and soak the entire surface of the printed circuit board with solvent. This solvent is an effective detergent and does not react chemically with the materials they dissolve; then the use of pumice or Salt scrubbing, this step removes inorganic substances such as particles and oxides and helps to remove oil; the next step is to rinse the printed circuit board with water and then use a brush to remove the fine particles of pumice. All of these steps are only supported on the edge of the printed circuit board being cleaned, and rubber gloves should be used as much as possible.

In order to remove residual alkali and metal oxides, a clean surface is prepared for image transfer and the board should be pickled in hydrochloric acid (concentration 10%). The final cleaning process is best accomplished using deionized water. Cleaning with tap water may result in a risk of failure caused by water impurities. The final step in the cleaning process is drying. The drying usually uses compressed air to blow the surface of the substrate. The air line of the compressed air system should have a filter that eliminates grease contamination from the compressor. For complete drying, keep the printed circuit board in an oven at a temperature of 90°C for approximately 15 minutes.

Solvent vapors are toxic, even known as air pollutants. Therefore, when using tanning agent vapors during operation, care must be taken not to inhale vapours, and sufficient air circulation should be ensured so that the maximum vapour concentration does not exceed 100 x 10-4%.

Degreasing can also be achieved by using a rinsing solution for bubbling, which is achieved by chemical reactions of organic contaminants and mash. It is very effective in removing oils and greases and does not cause any serious air pollution.

Vapor degreasing always cleans the substrate with pure solvent and is an improvement over the cold flux cleaning process. The degreasing part is heated to the boiling point of the grease solvent, so the drying of the substrate is faster than the cleaning of the substrate by the cold solvent. The steam degreasing equipment can also use an ultrasonic agitation system. The agitation of the ultrasonic agitation system is accomplished by acoustic waves.

Second, machine cleaning

During machine cleaning, it is typical to use a grinding brush to clean the machine. Grinding Figure 7-2 Use solvent strips, such as corundum, corundum, alumina, and silicon carbide to clean the substrate. These grinded, artificially cleaned abrasive materials can diffuse into nylon or similar plastic materials, and the bristle structure used is a flat sheet or filament. Before the dry film resist layering, a 320 mesh silicon carbide filament abrasive brush is usually used to clean the copper foil surface. The different types of machine cleaning operations are as follows:

1) Polishing

2) Brushing

3) Polishing or sanding

4) Deburring or scrubbing

5) Scrub

1. Polishing

This process improves its appearance by smoothing the metal surface. Polishing wheels (cotton cloth) are usually used for polishing.

Brush light

This process uses a rotating non-wire brush, such as a nylon brush to smooth the metal, and the wire brush is usually wet. For very dark metal surfaces, use a 3F or 4F pumice powder slurry for brushing. Although this can remove particulate matter very well, it can also clean out heavy oxides or other metal contaminants, but it cannot completely remove organic contaminants such as oils and greases. In fact, these contaminants remain in the brush, so it is recommended to use a solvent to remove oil before brushing.

3. Polishing or sanding

Polishing refers to the use of a cotton wheel to polish the metal surface, changing from a low-gloss product to a high-gloss product. This method removes large amounts of inorganic contaminants and particulate matter and also helps remove the burn marks around the borehole. Polishing can be done using electric handheld vibrators.