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Home > Blog > Ultimate Guide to Selective Gold Plating PCBs [2022 Updated]

Ultimate Guide to Selective Gold Plating PCBs [2022 Updated]

PCBONLINE Team

Thur, Sept 22, 2022

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Selective gold plating is called "selective" because it can apply to part of the PCB pads. What is PCB selective gold plating? What's the difference between gold plating, immersion gold, and PCB gold fingers? And when to use selective gold plating on PCBs? This article unveils PCB selective gold plating, and you will find advantages of selective gold plating PCBs.

Part 1: PCB Selective Gold Plating vs Gold Fingers vs Immersion Gold

When dealing with PCBs, you must have heard of selective gold plating, gold fingers, and immersion gold. Are you a little messed up with the three PCB surface finishes? Well, you can clearly distinguish them now.

selective hard gold plating vs immersion gold

Selective gold plating, also called hard gold plating or gold plating, is electroplating a nickel coating and then a gold coating on the required PCB pads. We call it selective because it happens before the solder mask printing and can apply to part of the PCB pads requiring it. And we call it hard gold because this surface finish is hard and wear-resistant. The gold takes up about 1% of the hard gold plating contents.

Note
Some people still insist that gold plating includes hard gold plating and soft gold plating. This statement is outdated. Now gold plating only means selective hard gold plating. Soft gold plating is electroplating the whole PCB and it is not selective at all, and what's more, it is not in use now.

On the contrary, immersion gold, or ENIG (electroless nickel immersion gold), or soft gold, is depositing a nickel coating and then a gold coating on the PCB pads or other areas with chemical reactions. The gold thickness is larger than selective gold plating, and we call it soft gold. ENIG has a golden color and looks brighter than selective gold plating. Also, the solderability of ENIG is better than selective gold plating.

Now, what about gold fingers? Gold fingers belong to selective hard gold plating and are a column of hard gold pads on the PCB edge with a 45° bevel. From the PCB manufacturer PCBONLINE, you can also choose the bevel of 20° or 30°. PCB gold fingers are also selective and serve connection purposes.

PCB gold fingers bevel

A clear comparison table of selective gold plating, immersion gold, and gold fingers is below.

Selective gold plating
Immersion gold
Gold fingers
Other names
Hard gold, gold plating, hard gold plating, electroplating gold
Soft gold, ENIG, chemical gold
Edge connectors
PCB surface finish
Electroplating a nickel coating and a gold coating on PCB pads
Depositing a nickel and a gold coating by chemical reactions
Belongs to hard gold plating
Outlook
Less golden
Golden
Less golden; a row of pads on the edge
Thickness
3μm to 50μm
1μm, 2μm, and 3μm
According to IPC-4556, it is 32μm
Solderability
Good
Best
Good

Part 2: When to Use Selective Gold Plating on PCBs?

Selective gold plating brings good conductivity, wear resistance, corrosion resistance, and oxidation resistance to a PCB. If your PCB needs these characteristics, apply selective gold plating. When to use selective gold plating:

Selective gold plating can be used for button and keyboard PCBs that withstand frequent operations and have to be durable. For example, the below selective gold plating PCBs manufactured by PCBONLINE with a 10μm hard gold thickness are used for industrial control system mainboards.

gold plating PCB industrial keyboard

Selective gold plating can be used on gold finger PCBs that are used for connection/plug-in and require good conductivity and wear resistance. For example, the gold fingers of data storage card PCBs below use a 32μm hard gold thickness.

gold finger PCBs

Selective gold plating can be used for keyboard PCBs that require different button hardness. For example, the metal dome array PCBs used for medical equipment use selective gold plating surface finishes. The buttons that are pressed and released frequently use hard gold plating, and the rest buttons that are used less frequently use immersion gold.

selective gold plating PCB for medical keyboard

If you can't ensure which PCB surface finish and thickness meet your PCB requirements, feel free to ask for suggestions from PCBONLINE. Our experienced CAM engineer will help according to your PCB design and expected product.

Part 3: One-Stop Selective Gold Plating PCB Manufacturer

If you need selective gold plating PCBs, keep in mind that only a few PCB manufacturers can buy gold salts (K[Au(CN)₂]) and have a sewage treatment system for hard gold plating. Most PCB factories can't complete selective gold plating PCB fabrication independently, but PCBONLINE does.

PCBONLINE gold plating PCB factory

PCBONLINE is a one-stop PCB and PCBA manufacturer that can apply selective gold plating on PCBs. Founded in 1999, PCBONLINE has two large advanced PCB manufacturing bases and one PCB assembly factory.

PCBONLINE can be your selective gold plating PCB supplier from PCB prototype to bulk production with these advantages:

    • Our PCB manufacturing base in Jiangsu has our gold plating lines, sewage treatment system, and fabrication qualification authorized by environmental protection sectors.
    • We can custom apply selective hard gold plating including gold fingers with a thickness of 3μm to 50μm.
    • We will review your Gerber and provide free PCB design for manufacturing (DFM) before PCB fabrication.
    • Besides selective gold plating, we can provide selective PCB surface finishes, such as OSP/immersion gold, OSP/lead-free HASL, etc.
    • We offer competitive prices because we can independently fabricate selective gold-plating PCBs.

If you have any PCB or PCBA inquiries and require selective gold plating, gold fingers, immersion gold, and selective surface finishes, please contact PCBONLINE by email at info@pcbonline.com to meet your fabrication needs.

Conclusion

Hard gold plating is called "selective" because it can apply to only part of the PCB pads, and the rest PCB pads can use other surface finishes. We hope this concise guide to selective gold plating PCBs clarifies the PCB selective gold plating, immersion gold, and gold fingers, and you can figure out when to use gold plating on PCBs. If you have more questions, feel free to discuss them in the comments below or chat with us online.


© This article is an original work of the PCBONLINE team. Please indicate the author PCBONLINE if you reprint. If the article is reproduced without permission or indicating the author's source, PCBONLINE reserves the right to investigate the infringement.