PCB Surface Finishes: How They Protect Copper and Boost Performance

Jul 16,2021

Printed circuit boards (PCBs) use copper traces extensively in pads, holes, and ground plains. If exposed directly to the environment, the copper traces may get oxidized. This can cause a performance reduction in copper-coated PCBs. To avoid this, the copper surface is often finished with a protective layer, generally known as PCB surface finish. There are different types of PCB surface finishes that offer different benefits. When it comes to result-centric PCB fabrication, different types of PCB surface finishes are chosen based on required performance parameters. This post discusses different types of PCB surface finishes and their advantages which make them suitable for specific applications.

Importance of PCB Surface Finishes

PCB surface finishes are important for many reasons. They help: 

• Protect the copper surface against oxidation.
• Protect the circuitry and mounted components against corrosion.
• Provide a solderable surface for component mounting.

Although the function of all types of PCB surface finishes remains the same, the performance parameters of the PCBs can change with different surface finishes. Let us discuss the types.

Different Types of PCB Surface Finishes and Their Advantages

The types of PCB surface finishes are listed below. 

• Hot Air Solder Leveling (HASL):

  Hot air solder leveling (HASL) is one of the most popular PCB surface finishes. In this method, the PCBs are submerged in molten lead or tin solder. Once the molten solder is deposited on the PCB surface, hot air is blown over the solder using hot-air knives. This helps in the uniform distribution of the deposited solder layer and removes excess solder material.

• Benefits
  • It offers excellent soldered surface finishing.
  • It offers a wide window of solder applications.
  • It is the least expensive surface finish.


• Lead-free Hot Air Solder Leveling:

  It is HASL without lead. In this, the process of application remains the same, whereas the molten lead solder is replaced with Tin-Nickel, Tin-Copper, or Tin-Copper-Nickel Germanium, etc.

• Benefits
  • It is the Restriction of Hazardous Substances (RoHS) directive-compliant PCB surface finish.
  • It allows multiple thermal excursions for the solder deposited PCB.


• Organic Solderability Preservative (OSP):

  Organic Solderability preservative (OSP) surface finish is the one where water-based cognatic solder material is used. A thin layer of organic solder material is applied to PCBs to prevent oxidation of the copper surface. The organometallic layer is applied to the copper surface by using a continuous application process.

• Benefits
  • It offers the most eco-friendly surface finish as compared to all PCB surface finishes.
  • The organometallic layer can be reapplied.
  • It a cost-effective process.
  • It secures the copper surface prior to the actual soldering process.


• Immersion Tin (ISn):

  This surface finish is achieved by depositing a thin layer of molten tin on the copper surface. Due to its simple application, it is ideal for small components as well.

• Benefits
  • This is one of the most affordable surface finishes available.
  • It works excellent with ball grid arrays (BGAs), fine pitches, and miniature components.


• Immersion Silver (IAg):

  In this type of surface finish, the layer of molten silver solder is deposited on a copper surface. Silver does not react with copper and therefore, this surface finish is as good as a lead-free surface finish.

• Benefits
  • It can be reapplied.
  • It is suitable for small components.
  • If placed in anti-tarnish packaging, it can last for 6-12 months.


• Electroless Nickel Immersion Gold (ENIG):

  Electroless nickel immersion gold (ENIG) PCB surface finish is a two-layer coating process. In this type of surface finish, 2-8 µinches of Gold (Au) is coated over 120-240 µinches of Nickel. The first layer of nickel protects the copper surface of PCBs and the gold layer protects the nickel layer during long-term storage.

• Benefits
  • It offers excellent flatness.
  • It complies with RoHS guidelines.
  • It extends the shelf life of the PCB to several years.
  • It can be plated through holes (PTH).
  
  

  Now that all the types of PCB surface finishes are discussed along with their benefits, you can certainly choose the one that suits the best for your application. However, regardless of the surface finish you choose, the quality must be a priority. This can be easily assured by partnering with trusted PCB assembly services. Creative Hi-Tech is a leading PCB assembly and fabrication company that specializes in custom PCB manufacturing. The experts at the company will help you choose the right PCB surface finishes for your application.

Related Blog Posts: 

• What Do You Know About Different Types of PCB Surface Finishing –I?
• What Do You Know About Different Types of PCB Surface Finishing –II