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Top 6 PCB Surface Finish: Pros and Cons

Table of Contents

PCB surface finish is to provide the coating or the protective layer to the PCB surface, protecting the copper surface from being oxidized. An oxidised PCB copper layer can affect its electrical performance and even lead to PCB failure. Therefore, it is crucial to choose a reliable and appropriate surface finish method in order to maintain stable operation and prolong the PCB’s lifespan.
This article will provide information on surface finish on PCB, its types, comparison between diferent types and some considerations for you to choose a suitable surface finish.

What is PCB Surface Finish?

Surface Finish in PCB refers to the coating or treatment applied to the copper surface of PCB. It protects them from oxidation like a solder mask on PCB and also improves their solderability. In PCB manufacturing, PCB finish is one of the most critical factors. It influences the overall performance of the circuit board, including reliability and solderability.

The benefits of PCB surface finish include:
  • To prevent oxidation at the surface of copper
  • To help in soldering the components quickly.
The selection of surface finish depends on the specific requirements and the manufacturing process.

PCB Surface Finish Types

The most common types of PCB surface finish are given below:

PCB Surface Finish Types

Hot Air Soldering Leveling (HASL)

HASL is the conventional type of surface finish applied to PCB. It involves the coating of the PCB using molten solder. It uses hot air to remove the excess solder, and it then leaves a thin layer on the surface of copper.

HASL Surface finish is of two types: lead-based solder and lead-free HASL.

Pros

Cons

  • Uneven surface not suitable for fine-pitch components
  • Thermal stress during processing could affect some electronic components

Electroless Nickel Immersion Gold (ENIG)

PCB Surface Finish ENIG

The RoHS compliances and the features of this ENIG made it one of the most popular choices as a PCB finish for PCB. It consists of a thick layer of nickel and gold. The gold coating over the nickel protects the nickel from oxidation. Likewise, nickel protects the copper and helps to sell it to its surface securely.

Pros:

  • Durable and long shelf life
  • Can bear harsh environment

Cons:

  • It is expensive since it has a gold immersion process
  • Signal loss for signal integrity

ENEPIG:
Electroless Nickel Electroless Palladium Immersion Gold

ENEPIG is the variation of ENIG. It includes three layers: electroless nickel, followed by a layer of palladium, and immersion gold on the copper surface. The combination of this layer provides the strongest bondable option. Although it is quite expensive, it offers better solderability with a flat surface. It is mainly used for high-frequency applications.

Pros:

  • Excellent for wire bonding.
  • Suitable for fine-pitch components.
  • Extremely Flat Surface

Cons:

  • It is a complex and costly process.
  • Challenges in thickness control.

Immersion Silver (ImAg)

Immersion Silver includes a thick layer of silver on the copper surface. It provides good solderability and a flat surface for the fine-pitch components.

Pros:

  • Good solderability.
  • Flat surface suitable for fine-pitch components.

Cons:

  • Susceptible to tarnishing.
  • Limited shelf life.

Organic Solderability Preservative (OSP)

PCB Surface Finish OSP

It is an organic coating used in PCB copper traces to provide good solderability and protection for oxidation. It contains an organic acid that forms a protective layer on the PCB surface after reacting with copper traces. It thus prevents the copper from getting oxidized from the air.

Pros

  • Effective for surface mount technology due to its flat surface
  • Lower thermal stress on PCB
  • Provides uniform coating thickness across the PCB surface

Cons

  • Limited Shelf Life around 6-12 months
  • At higher humidity levels, it could absorb moisture
  • Oxidation ability can decline over time

Hard Gold

Hard Gold includes the gold layer, which is plated over the layer of nickel coating. It is a gold alloy with iron, nickel, and cobalt. It provides a tough friction resistance compared to other surface finishes. This finish is a perfect option when a PCB is intended to be inserted into another board, like RAM or expansion cards. Based on the application, the thickness of this finish could vary.
Pros

  • Durable and tough
  • Longer shelf life
  • Lead-free PCB finish

Cons

  • Expensive with poor solderability
  • Requires more processing time
  • It provides an uneven surface

Comparison of PCB Surface Finish Technologies

RequirementsHASLENIGENEPIGImAgImSnOSP
Cost-Sensitive ProductYESNONOYESYES
YES
High Volume RequiredNONONOYESYESYES
Cosmetics of Surface FinishYESNOYESNOYESYES
Lead-Free Wave SolderYESYESYESYESNONO
Fine Pitch Components UsedNOYESYESYESYESYES
Wire Bonding RequirementNOYESYESYESNONO
High Yield ICTYESYESYESYESYESNO
Lead-Free Shock/DropYESNONOYESYESYES

Factors to Consider
while Selecting PCB Surface Treatment

PCB surface determines the long-term reliability and working of the PCB. Thus, before selecting the PCB finish based on your requirements, you need to consider various things, including:

Design & Application Factors

  • Environmental Needs: Humidity, chemical exposure, thermal cycling
  • Component Constraints: Fine-pitch/BGA support, wire bonding (ENIG/ENEPIG only)
  • Electrical Performance: Signal loss tolerance

Performance & Reliability

  • Solderability: Prioritize HASL for manual assembly, OSP/ImAg for SMT
  • Rework Potential: Exclude Immersion Tin if repairs are anticipated
  • Durability: Corrosion/wear resistance (e.g., Hard Gold for edge connectors)
  • Planarity: Ultra-flat surfaces (ENEPIG/OSP) for HDI designs

Logistics & Economics

  • Cost-Quality Balance: Match finish to product tier
  • Shelf Life: OSP (6-12mo) vs. ENIG (12+mo); plan inventory accordingly
  • Storage: Humidity controls for OSP/ImAg; anti-tarnish packaging for silver

Manufacturing Alignment

  • Assembly Process: Validate compatibility with SMT, wave soldering, etc.
  • Standards Compliance: IPC-4552 (ENIG), IPC-4551 (ImSn), RoHS 2024
  • Supplier Qualifications: Audit manufacturer’s process controls and certification
surface finish selection

Conclusion

As 5G, automotive electronics, and RoHS 2024 standards push performance limits, your choice between HASL’s cost-efficiency, ENIG’s durability, or OSP’s planarity directly impacts product lifespan and field failure rates.
At ELE PCB, we’ve helped lots of clients reduce surface-finish-related failures through using high class electroplating potions and surface treatment potions. The pollution and oxidation of the board surface, black nickel, abnormal nickel thickness, SCUM (shadow) and other problems are strictly controlled during the operation process.
If you have any queries or are confused regarding PCB surface finish, contact us with your requirements. We will ensure your PCB surface finish meets your needs.

FAQs

A1: Electroless Nickel Immersion Gold (ENIG) is one of the most commonly used surface finishes. Its layer of Gold protects the nickel and provides a lower resistance for storing the thin Gold. This lead-free option results in a long-lasting and durable surface finish. ENIG surface finish is growing with the growth and use of RoHS regulations. It is also the best option for RF PCB.
A2: The typical thickness of PCB surface finish is 100 micro inches. The thickness of surface finish can vary depending on the types of surface finish and applications. HASL, for example, has a thickness of 1-40 micrometers. However, it depends based on the specific requirements. On the other hand, ENIG has a thickness of 3-6 micrometers, and the gold layer has a thickness of 2-6 microinches. Thus, always refer to the specifications provided by your PCB manufacturers to ensure the consistency of your surface finish.
A3: HASL is the cheapest surface finish of all types. It is commonly available and very economical too. However, it has some drawbacks, like not being RoHS compliant and providing an uneven surface. Besides, it has a limited shelf life.
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Rashila
I am an Electrical and Electronics Engineer, and I have 5 years of work experience with electronics and communication jobs. I'm the full time content creator of ELE company.
About Benjamin

Benjamin is the general manager of ELE PCB, a leading PCB design and manufacturing company based in China. He has over 10 years of experience in the PCB industry, and has been involved in various projects.

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