PCB Surface Finish Options
The surface finish protects exposed copper and provides the solderable or contact surface used during PCB assembly. The right finish depends on component pitch, soldering process, storage requirements, contact wear, wire bonding and the electrical requirements of the application. PCB Company UK supports common finishes including HASL, lead-free HASL, ENIG, OSP, immersion silver, immersion tin and gold finishes where required by the design.
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Finish
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Description
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| HASL (Hot Air Solder Leveled) |
Solder is deposited on features that are not covered with Solder Mask. Solder Thickness varies from 0.2 to 1.2 mils. This variation is due to board circuit density and aspect ratio. Solder consists of 63%/37% eutectic Tin/lead |
| OSP (Organic Solderability Preservative) | A transparent organic coating is deposited on features that are not covered with a solder mask. |
| ENIG (Electrolytes Nickel/Gold) | Electrolysis of nickel and electrolysis of gold are deposited on features that are not covered with Solder Mask. The thickness for Nickel is between 80 and 150 micro inches, and the gold thickness is 3-6 micro inches. |
| Gold Flash | Electrolytic nickel-gold deposited on solderable features. Typically, 150-200 micro inches of nickel is deposited, and 5-10 micro inches of Hard gold. Gold flash is applied to features after pattern Copper plating. |
| Immersion Silver | Silver is deposited on features not covered with the solder mask. The thickness of silver is 4 to 20 micro inches. |
| White Tin | Immersion tin is deposited on features not covered with the solder mask. Thickness is typically 30-40 micro inches. |
| Carbon Ink for Key pad application |
A conductive carbon paste is applied on selective pads for contact purposes, e.g.. Keypads of calculators, etc. |
| Wire Bondable Soft Gold |
Electrolytic soft gold is plated on features that require bondable gold for a wire bonding application. Depending on the type of wire bonding used, the thickness of gold varies from 20 to 50 microns. Nickel thickness is between 150 and 250 micro inches. |
How to Select a PCB Surface Finish
Use the component technology and end application to guide the finish choice. Fine-pitch surface-mount designs generally benefit from a flat solderable surface. Edge contacts or wear surfaces may require a gold finish designed for repeated contact. OSP and immersion finishes can suit applications where a flat copper-protective coating is preferred. If the board will be wire bonded, specify the wire-bonding process and required gold finish clearly.
If you are unsure, include the assembly method, component pitch, connector/contact requirements and operating environment with the manufacturing data so the finish can be reviewed against the complete build.