In circuit board manufacturing, various electroplating methods are employed to enhance performance, durability, and contact quality. This article focuses on four specialized electroplating methods commonly used in PCB (printed circuit board) welding processes.

1. Finger-Ring Electroplating

Finger-ring electroplating involves plating rare metals, such as gold, on the edge connectors or gold fingers of circuit boards to provide low contact resistance and high wear resistance. This method is also known as protruding part electroplating. The typical process includes:

1. Stripping: Remove any tin or tin-lead coatings from the contacts.
2. Rinse: Clean the contacts with water.
3. Abrasive Scrubbing: Scrub the surface to remove debris.
4. Activation: Soak in a 10% sulfuric acid solution to activate the contacts.
5. Nickel Plating: Apply a 4-5μm nickel layer.
6. Rinse: Use demineralized water for cleaning.
7. Gold Penetration: Treat with a gold penetration solution.
8. Gold Plating: Electroplate gold onto the contacts.
9. Final Cleaning: Rinse with clean water.
10. Drying: Dry the plated contacts.

In modern PCB manufacturing, alternative plating methods like lead plating and button plating have started to replace traditional gold finger plating.

2. Through-Hole Electroplating

Through-hole electroplating is crucial for creating conductive pathways in drilled holes on PCB substrates. This process, also called hole wall activation, involves:

• Drilling: As the drill creates holes through the copper foil and substrate, heat causes the resin to melt, coating the hole walls with debris.
• Stain Removal and Etch-Back: These processes are used to clean and prepare the hole walls for electroplating.

A more advanced method for prototyping involves using low-viscosity conductive ink that forms a continuous conductive coating inside the holes. This approach eliminates the need for multiple chemical treatments, allowing the holes to be directly electroplated after a single application of the ink, followed by heat curing.

3. Reel-to-Reel Selective Plating

Reel-to-reel selective plating is used to plate the pins and leads of electronic components, such as connectors and integrated circuits, for improved corrosion resistance and contact quality. This method, which can be manual or automatic, is highly cost-effective for batch processing.

The process involves:

1. Punching: The metal foil is punched to the required thickness.
2. Cleaning: The surface is cleaned using chemical or mechanical methods.
3. Selective Plating: The desired area is plated with materials like nickel, gold, silver, or rhodium.

A resist film is applied to the non-plated areas, ensuring that only the selected metal foil parts receive the plating.

4. Brush Plating

Brush plating is another selective electroplating method used for repairing and modifying specific PCB areas. Unlike traditional plating, where the entire part is immersed in the electrolyte, brush plating targets only specific areas. It is commonly used to plate precious metals on edge connectors or in PCB repair processes.

Key aspects of brush plating include:

• Selective Application: Only the desired areas are plated.
• Special Anode: An inactive anode (like graphite) wrapped in absorbent material is used to apply the plating solution.
• Localized Plating: This technique ensures no impact on non-targeted PCB areas, making it highly useful for repair and customization.