Surface Finishes

What Are PCB Surface Finishes?

PCB surface finishes are protective coatings applied to the exposed copper areas of a printed circuit board. Their main purpose is to prevent oxidation, protect solderable pads, and support reliable assembly. Without the right finish, exposed copper can degrade over time, which can affect solderability, electrical contact performance, storage life, and long-term reliability.

Importance of Surface Finish Selection

Choosing the right PCB surface finish is important because different finishes perform differently in terms of solderability, flatness, cost, RoHS compliance, storage life, and suitability for fine-pitch components. Some finishes are better for low-cost standard boards, while others are preferred for flat pad requirements, high-density layouts, wire bonding, keypad contacts, or demanding assembly conditions.

How to Choose the Right Surface Finish

The best surface finish depends on your board design, assembly method, storage conditions, and end-use application. For many standard PCB builds, HASL remains a practical and cost-effective option. Where a flatter surface is required for fine-pitch components, ENIG, OSP, immersion silver, or immersion tin are often considered because planarity becomes more important during assembly.

Surface Finishes

Finish	Description
HASL (Hot Air Solder Leveled)	Solder is deposit on features that are not cover with Solder Mask. Solder Thickness varies from 0.2 to 1.2 mils. This variation is due to board circuit density, aspect ratio. Solder consists of 63%/37% eutectic Tin/lead
OSP (Organic Solderability Preservative)	A transparent organic coating is deposit on features that are not cover with solder mask.
ENIG (Electrolysis Nickel/Gold)	Electrolysis nickel and Electrolysis gold is deposit on features that are not cover with Solder Mask. Thickness for Nickel is between 80 to 150 micro inches and Gold thickness is 3-6 micro inches.
Gold Flash	Electrolytic nickel-gold deposit on solderable features. Typically 150-200 micro inches of nickel is deposit, and 5-10 micro inches of Hard gold. Gold flash is apply to features after pattern Copper plating.
Immersion Silver	Silver is deposit on features not cover with solder mask. Thickness of silver is 4 to 20 micro inches.
White Tin	Immersion tin is deposited on features not covered with Solder mask. Thickness is typically 30-40 micro inches.
Carbon Ink for Key pad application	A conductive carbon paste is apply on selective pads for contact purposes, e.g.. Keypads of calculators, etc.
Wire Bondable Soft Gold	Electrolytic soft gold is plate on features that require bondable gold for wire bonding application. Depending on the type of wire bonding use, the thickness of gold varies from 20 to 50 micro inches. Nickel thickness is between 150 to 250 micro inches.