When you select a PCB surface finish, you control how exposed copper pads perform during assembly and long-term use. Each finish coats areas not covered by solder mask, creating a solderable surface and limiting copper oxidation.
Hot Air Solder Leveling (HASL) applies a layer of eutectic tin‑lead solder to exposed features. The solder thickness typically ranges from 0.2 to 1.2 mils, and it can vary with circuit density and hole aspect ratio. This process leaves a metallic coating that supports conventional soldering methods.
Organic Solderability Preservative (OSP) uses a thin, transparent organic film. You gain a flat surface suitable for fine-pitch components, while the coating temporarily protects copper until soldering.
Electroless Nickel Immersion Gold (ENIG) deposits nickel followed by a thin gold layer. Nickel usually measures 80–150 microinches, with gold at 3–6 microinches. The nickel acts as a barrier, and the gold preserves solderability.
Electrolytic Nickel/Gold (Gold Flash) builds a thicker nickel base, commonly 150–200 microinches, topped with 5–10 microinches of hard gold. Manufacturers apply it after pattern copper plating to reinforce solderable features.
Other metallic finishes include:
- Immersion Silver: 4–20 microinches of silver
- Immersion Tin (White Tin): 30–40 microinches of tin
For specialized needs, you can specify:
- Carbon ink coatings on selected pads for keypad contacts
- Wire bondable soft gold, with 20–50 microinches of gold over 150–250 microinches of nickel, for reliable wire bonding
Your choice affects soldering behavior, surface flatness, and compatibility with specific assembly processes.
