10 Types of PCB Surface Finishes: Benefits and Drawbacks

PCBs, also known as Printed Circuit Boards, have a wide range of industrial applications. PCBs must be completely covered with proper surface finishes as they are designed with copper traces. While increasing the overall service life of PCB assembly, the right surface finishes also prevent copper oxidation/deterioration. Choosing the right surface finish can help ensure the PCB's performance, durability, and compliance. Here are 10 types of PCB surface finishes that manufacturers should consider while designing PCBs.

1. Immersion Silver

Among well-known PCB surface finishes, immersion silver is a popular one that covers the copper surface of PCB with a thin layer of silver chemical deposits.

The advantages of using immersion silver as a PCB surface finish are:

• Better electrical conductivity
• A balance between efficiency and cost
• Helps in complex PCB designs

The disadvantages of immersion silver are:

• Limited shelf life.
• Can be sensitive to handling.

2. Hot Air Solder Levelling (HASL)

HASL is one of the conventional PCB surface finishes that dips PCB into a molten solder pot.

The benefits of using this surface finish include:

• Better shelf life
• Cost-effectiveness
• Improved solderability

HASL limitations are as follows:

• Uses lead which is not compliant with RoHS.
• The uneven surface is not suitable for fine-pitch elements.

3. Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG)

In the PCB industry, ENEPIG is used as a multi-layered surface finish.It uses nickel, palladium and gold layers as coverings for the copper traces.

Using ENEPIG as a PCB surface finish offers various advantages like:

• Enhanced corrosion resistance
• Multiple assemblies and increased reliability
• Versatility
• Lead-free and aligning with environmental standards

The limitations of ENEPIG are as follows:

• The plating process is complex.
• Expensive

4. Lead-Free HASL

It is an upgrade of conventional Hot Air Solder Levelling. It is basically a replacement for lead-containing solders.

The benefits of using this PCB surface finish are as follows:

• Offers a good shelf life
• Gives excellent solderability
• Complaint with RoHS regulations

Lead-free HASL also has disadvantages like:

• Higher melting point, causing a challenge during assembly.
• Surface finish irregularities.

5. Electroless Nickel Immersion Gold (ENIG)

ENIG is a widely used PCB surface finish that uses electroless plating method to place a thin layer of nickel is placed on the PCB’s copper surface.

The benefits of using ENIG include:

• Extreme flat surface for installing fine-pitch surface elements.
• High corrosion resistance, offering longevity.
• Lead-free and meeting environmental standards.

The demerits of ENIG include:

• Limited rework ability.
• Costly.

6. Electrolytic Wire Bondable Gold

A specialised PCB surface finish, Electrolytic Wire Bondable Gold, is used in applications that typically require wire bonding.

Using this PCB surface finish offers advantages like:

• Increased dependability
• High corrosion resistance
• Enhanced wire bonding components

The disadvantages of Electrolytic Wire Bondable Gold are:

• The process is precise and complex.
• Not suitable for soldering.

7. Immersion Tin

Immersion Tin is a PCB surface finish which has zero-lead soldering techniques.

Using immersion tin as PCB surface finish provides:

• Affordability
• Excellent solderability
• Environmental regulations and RoHS compliant
• High flat surface for mounting fine-pitch components

Immersion tin also has challenges like:

• Whisker growth
• Limited shelf life

8. Carbon Ink

Carbon Ink is not a standard surface finish for the entire printed circuit board. Rather, it is implemented in selected regions to provide unique capabilities.

Its benefits include:

• Offering flexibility in creating flexible PCBs.
• For designing conductive surfaces like touch screens and keypads.
• Economical than using metal.

The demerits of carbon ink are:

• These are sensitive to the environment.
• These are less conductive to metal finishes.

9. Organic Solderability Preservatives (OSP)

OSP is one of the surface finishes that is used in PCB production to prevent copper oxidation until soldering.

The advantages of OSP are as follows:

• Offers easy inspection of underlying copper.
• Free from lead and other harmful substances.
• Affordable.
• Offers flat surfaces for installing fine-pitch components.

The disadvantages of OSP include:

• Zero multiple reflow
• Limited shelf life

 10. Electrolytic Nickel/Gold (Hard Gold)

Hard Gold or Electrolytic Nickel/Gold is a type of PCB surface finish that is frequently used in applications requiring long-lasting and repetitive use. It involves the electroplating process of the nickel on the copper pads of PCBs.

This surface finish also offers some important advantages, such as:

• Prolonged shelf life
• Great durability
• Corrosion resistance

The cons of hard gold as PCB surface are:

• Too pricey
• Not suitable for soldering

Conclusion

Depending on the manufacturing process of PCBs, cost, durability and many other factors, choose a surface finish that is ideal for the PCB design. Furthermore, select a surface finish that prevents copper deterioration, as PCBs are made of copper traces.

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