Surface treatment in the production of high-frequency PCB (Printed Circuit Board) is a crucial step that directly affects the board’s solderability, corrosion resistance, and electrical performance. Surface treatment typically includes processes such as gold plating, tin plating, immersion gold, and immersion tin. Here are the main steps and considerations for surface treatment in high-frequency PCB production.

Main Steps in Surface Treatment
Cleaning

Before any surface treatment, the PCB surface must be thoroughly cleaned to remove oil, dust, and other impurities. Cleaning methods can include ultrasonic cleaning, solvent cleaning, or chemical cleaning.
Surface Activation

To ensure good adhesion of subsequent surface treatments, the surface should be activated after cleaning. Common methods include acid etching and plasma treatment, which can enhance surface energy and promote metal deposition.
Electroplating or Chemical Plating

Choose the appropriate plating layer according to design requirements. Electroplating is usually used for tin and gold plating, while chemical plating is often used for immersion gold and immersion tin.
Electroplating: The PCB is immersed in a plating bath, where an electric current reduces metal ions and deposits them onto the PCB surface.
Chemical Plating: This method uses chemical reactions to deposit metals onto the PCB surface without the need for electric current.
Post-Treatment

After surface treatment, post-treatment may be required, such as cleaning, drying, and passivation, to ensure the quality and stability of the plating.
In some cases, thermal treatment may be performed after plating to enhance the adhesion and durability of the coating.
Testing

Perform performance testing on the surface-treated PCB, including corrosion resistance, adhesion, and conductivity tests, to ensure that the treatment quality meets design requirements.
Considerations for Surface Treatment
Importance of Cleaning

Cleaning is the first step in surface treatment and must be thorough to prevent impurities from affecting the quality of subsequent plating.
Choice of Activation Treatment

Select an appropriate activation method to ensure sufficient surface energy, enhancing the adhesion of the plating.
Control of Coating Thickness

During electroplating or chemical plating, it is essential to strictly control the thickness of the coating to avoid it being too thick or too thin, which can impact electrical performance and solderability.
Environmental Control

Factors such as temperature, humidity, and gas composition during the surface treatment process can influence coating quality, so a stable treatment environment is necessary.
Testing and Quality Control

Regular quality testing should be conducted to ensure that the surface treatment quality of each batch meets standards, and adjustments to process parameters should be made to optimize production.

Common Surface Treatment Processes
Hot Air Solder Leveling (HASL)

This is a common surface treatment method where the PCB is immersed in molten solder and then excess solder is removed using hot air to achieve a smooth solder layer.
Considerations: Temperature control during HASL is critical; excessively high temperatures may damage the PCB substrate.
Immersion Gold

Immersion gold is a chemical plating method that provides excellent solderability and corrosion resistance. The immersion gold layer is usually thin but offers good conductivity.
Considerations: The deposition time and temperature for immersion gold need to be strictly controlled to ensure coating consistency and quality.
Tin Plating

Tin plating enhances the solderability of PCBs and prevents substrate oxidation. Tin layers can be applied through either electroplating or chemical plating.
Considerations: Thermal treatment after tin plating is necessary to enhance the durability and adhesion of the tin layer.
Silver Plating

Silver plating is critical for high-frequency applications due to silver’s superior conductivity compared to copper. It is typically used in high-frequency signal paths.
Considerations: Silver layers are prone to oxidation, so anti-oxidation treatments should be considered to ensure long-term stability.
Coating Treatments

In some cases, surface treatments also include applying protective coatings, such as polymer or other protective materials, to improve abrasion resistance and waterproofing.
Considerations: The choice of coating material should consider electrical performance, thermal stability, and environmental adaptability.
Common Issues and Solutions
Uneven Coating

Cause: This may result from inadequate cleaning, improper activation, or strict control of the plating process.
Solution: Enhance control over cleaning and activation processes, and conduct regular thickness testing to ensure consistency.
Poor Adhesion

Cause: Dirty substrate surface or insufficient activation.
Solution: Ensure thorough cleaning and activation treatment; repeat the process if necessary.
Coating Delamination

Cause: Insufficient coating thickness or poor material compatibility.
Solution: Select appropriate coating materials during the design phase and ensure coating thickness meets standards.
Corrosion Issues

Cause: Inadequate coating protection or environmental impacts.
Solution: Consider using anti-oxidation treatments and increasing protective coatings to enhance corrosion resistance.
Surface treatment for high-frequency PCB is crucial for the performance and reliability of circuit boards. By precisely controlling every aspect of cleaning, activation, plating, and post-treatment, it is possible to ensure that PCBs exhibit excellent electrical performance and stability in high-frequency applications. Adhering to strict process flows and considerations during production will contribute to enhancing the overall quality of the products.