ENIG vs Hard Gold: Pros and Cons of The Two PCB Surface Finishes

When you design PCBs (printed circuit boards) for different applications, you'll need to select proper PCB surface finishes on the copper pads, as different surface finishes are suitable for different applications. Immersion gold and hard gold plating are two common surface finishes that you may be confused about. This blog introduces and compares them, including their pros/cons and applications.

Immersion Gold (ENIG)

Pros: Smooth and flat surface, suitable for fine-pitch assembly, excellent welding performance, strong oxidation resistance, suitable for via filling of multi-layer PCBs

Cons: Higher cost than hard gold, poor wear resistance, delamination issue on the PCB pad if nickel sulfide compounds form between nickel and gold.

ENIG (electroless nickel immersion gold) is also called immersion gold. It includes the nickel layer at the bottom and the gold layer at the top. The ENIG process includes electroless nickel and then chemical depositing gold on the nickel.

In ENIG, the nickel layer is pure nickel or phosphorus nickel. Its thickness is 3-5 micrometers. It provides adhesion for the gold layer and improves conductivity and oxidation resistance. First, a very thin nickel layer is formed on the copper pad surface by electroplating. Then, a reducing agent (such as hydride or formaldehyde) is added to the nickel plating solution to reduce nickel ions to the surface to form the final nickel layer.

The gold layer in ENIG is pure gold though it is thin with a thickness of only 0.03-0.1 micrometers. It provides excellent conductivity and welding performance. During reflow soldering in the PCB assembly process, the gold layer in ENIG and the solder form an intermetallic compound with the copper pad, which ensures perfect soldering performance.

Applications of ENIG

ENIG is used as the surface finish for high-precision PCBs and those requiring highly stable electrical performance. Advanced PCBs such as flexible PCBs, rigid-flex PCBs, ceramic PCBs, and HDI PCBs usually use ENIG as their surface finish. The ENIG pads are used for BGA (ball grid array) and CSP (chip-scale package) assembly, micro connectors, wire bonding, etc.

Hard Gold

Pros: high wear resistance, oxidation resistance, good conductivity.

Cons: Not suitable for welding, because the added alloy can affect the welding performance. Higher cost.

The PCB surface finish hard gold is also called hard gold plating. It includes the nickel layer at the bottom and the gold layer at the top, which adhere to the PCB copper pad's surface by electroplating.

In hard gold, the nickel or nickel alloy layer has a thickness of 3-5 micrometers. It provides hardness, improves wear resistance, and prevents diffusion between gold and copper. Besides, it provides good adhesion for gold layer electroplating.

The gold layer in hard gold has a thickness of 0.5-3 micrometers. It is not pure gold but has 0.2%-1% cobalt or nickel. It provides high wear resistance to the surface finish, prevents oxidation, and ensures good conductivity.

Applications of hard gold

Hard gold PCBs are used in devices that require frequent contact and friction. The PCB pads with the hard gold surface finish are used for edge connectors, connector contact points, switch buttons, metal conductive rails, and contact surfaces of high-frequency radio frequency devices.

Hard Gold vs ENIG

If your design requires high soldering performance and high precision, choose ENIG. If the design requires high wear resistance and frequent contact, choose hard gold. Below is a comparison table that briefly compares them.

One-Stop Advanced PCB Manufacturer Good at ENIG and Hard Gold

If you are looking for a professional PCB manufacturer to work on your project at one stop and provide engineering support, you can work with the advanced PCB and PCBA manufacturer PCBONLINE, who deals very well in ENIG, hard gold, and all the other surface finishes.

PCBONLINE is a PCB source factory manufacturer founded in 1999. It has two large advanced PCB manufacturing bases, one PCB assembly factory, stable supply chains, and an R&D team.

No matter what quantity of boards you want, PCBONLINE offers free design for manufacturing (DFM) and one-on-one engineering support to ensure the smooth manufacturing process and successful result of your project. To get a quote for your PCB or PCBA project, contact info@pcbonline.com.

Conclusion

Both ENIG and hard gold are common PCB surface finishes. This blog introduces and compares them in detail, and you have learned the pros and cons and applications of ENIG and hard gold PCBs. No matter what surface finish your PCB requires and what type of PCB you want, you can work with the one-stop advanced PCB manufacturer PCBONLINE. If you have questions about your PCB surface finish, chat with PCBONLINE from the online chat window.