What is Gold Thickness and Surface Finish?

When it comes to printed circuit board (PCB) design and manufacturing, 

one critical factor that often determines the success of a project is the choice of surface finish. Among the many options available,

 hard gold plating stands out for applications requiring durability and high wear resistance, 

such as edge connectors and contact points. 

But how do you determine the right hard gold plating thickness for your PCB? The optimal thickness balances cost, 

performance, and reliability, typically ranging from 0.75 to 1.25 microns (30 to 50 microinches) for most applications, 

though specific needs may vary. In this comprehensive guide, we’ll dive deep into the nuances of hard gold plating thickness, 

explore industry standards, measurement techniques, cost considerations, and how to achieve the best results for your designs.




What Is Hard Gold Plating and Why Does Thickness Matter?
Hard gold plating is a surface finish applied to specific areas of a PCB, such as gold fingers or contact pads, 

to enhance durability and conductivity. Unlike soft gold, which is purer and used for bonding applications, 

hard gold is alloyed with other metals like cobalt or nickel to increase its hardness. 

This makes it ideal for high-wear areas that endure frequent mechanical stress, such as connectors that are repeatedly inserted and removed.


The thickness of the hard gold layer directly impacts several key factors:

Durability: Thicker layers withstand more wear and tear, extending the lifespan of the PCB in demanding applications.
Conductivity: Gold offers excellent electrical conductivity, but too thin a layer may not provide consistent performance over time due to wear.
Cost: Gold is expensive, and thicker plating significantly increases manufacturing costs.
Reliability: The right thickness ensures reliable connections without failures caused by insufficient material or excessive buildup.
Finding the sweet spot for hard gold plating thickness is crucial for meeting performance requirements without breaking the budget. Let’s explore how to achieve this balance.

Why the Gold Thickness Should Be ≥ 2U”

In PCB wire bonding, the gold thickness requirement directly affects bonding reliability and overall production yield.

Ensuring Bonding Reliability

When the gold layer is thick enough, it forms a stable atomic-level bond with the gold wire during the gold wire bonding process. A thicker gold layer reduces failures caused by surface contamination, oxides, 

or plating defects, ensuring long-term bonding reliability in electronic products.

Preventing Nickel Exposure

During the wire bonding process, ultrasonic energy and pressure wear the surface of the gold finish. A gold thickness of 2U+ helps prevent the gold layer from being worn through and exposing the underlying nickel (or copper), 

which is critical for maintaining bonding reliability and product lifetime.

Solderability and Stability

A thicker gold layer also withstands high-temperature environments better, preventing oxidation, discoloration, or degradation. This helps maintain stable electrical and mechanical performance after PCB wire bonding.

ENEPIG vs ENIG for Gold Wire Bonding

The choice of PCB surface finish for wire bonding directly affects the yield and reliability of chip packaging processes such as COB bonding. In most PCB manufacturing processes involving gold wire bonding, 

the ENEPIG surface finish is significantly superior to ENIG, especially for high-reliability or fine-pitch bonding.

The primary difference between ENIG and ENEPIG is the “black pad” issue:

During the ENIG process, strong oxidizers in the immersion gold bath can attack the electroless nickel layer—particularly along grain boundaries—causing excessive corrosion and forming a brittle, phosphorus-rich layer.

In an ENEPIG surface finish, the immersion gold reaction occurs on top of the palladium layer rather than directly on nickel. Palladium is a noble metal and is not corroded, preventing nickel damage and eliminating the black pad problem.

Conclusion

If your PCB production requires gold wire bonding, please make sure to include a note when placing your order or specify it clearly in your design files. For the best bonding reliability, 
we recommend using a gold thickness of at least 2U’’ and select the ENEPIG surface finish.
At Hycxpcba, we’re committed to helping you navigate the complexities of PCB surface finishes. With expertise in hard gold plating and a focus on precision, 
we can support your project from design to delivery. Reach out to our team to discuss your requirements and discover how we can help bring your vision to life with the perfect plating solution.