An Introduction to 4-Layer Immersion Gold PCB

As an integral part of electronic circuits, the importance of printed circuit boards has grown immensely. There are various criteria to select them for a project. However, selection on the basis of surface finish is gaining popularity. The surface finish is a coating done on the outermost layer of the PCB. The surface finish performs two tasks – protecting the copper circuitry, and serves as a solderable surface during the PCB assembly. There are two main types of surface finishes – organic and metallic. This post discusses a popular metallic PCB surface finish – immersion gold PCB.

Understanding the 4- Layer Immersion Gold PCB

The 4 layer PCB comprises 4 layers with FR4 base materials, 70 um gold, and 0.5 OZ to 7.0 OZ thick copper substrates. The minimum hole size is 0.25mm, and minimum track/space is 4Mil.

A thin layer of gold is applied over nickel, which is plated onto the copper. The nickel serves as a diffusion barrier between copper and gold, and prevents them from mixing up. The gold gets dissolved during the soldering process. The typical thickness of nickel is between 100-200 micro inches, and the gold is 2-4 micro inches.

A Brief Introduction to the Method of Applying Gold Plating onto the PCB

The coating is deposited onto the surface of the FR4 material through a closely monitored chemical reaction. Also, the coating is applied after the application of solder mask. However, in some cases, the coating is applied before soldering, but that is very rare. The cost of this plating is higher when compared to other types of metallic plating. As the coating is done through electroless method, thus it is known as Electroless Nickel Immersion Gold (ENIG).

Uses of 4- Layer ENIG PCBs

These PCBs are used in Ball Grid Arrays (BGAs) and Surface Mount Devices (SMDs). The gold is considered a good conductor of electricity. This is why many circuit assembly services prefer this type of finish for high-density circuits.

Advantages of Immersion Gold Surface Finish

The following advantages of immersion gold surface finish make them popular with electrical assembly services.

  • No frequent dummy plating required.
  • Re-flow cycles are continuous.
  • Provides excellent electrical testability
  • Good Adhesion
  • Provides level plating around the circuits and pads.
  • Immersion finish provides excellent flatness.
  • Wire bondable.
  • Follows tried and proven application method.

You can contact an electronic expert or a reputed manufacturer of rigid flex circuit board to understand how 4-layer immersion gold PCBs can be an asset to your electronic assembly. Rigiflex Technology is a supplier of flexible, rigid, and rigid flex PCBs in the USA. The organization provides prototypes for custom PCBs and complete PCBs. For more information about 4-layer immersion gold PCBs, please visit, or contact the company at (714) 688-1500.