As a component of electronic circuit, the importance of printed circuit board has been greatly increased. There are multiple criteria for selecting them for projects. But options based on surface finish are gaining popularity. Surface finish is the coating done on the outermost layer of the PCB. Surface treatment accomplishes two tasks – protecting the copper circuit and serving as a weldable surface during PCB assembly. There are two main types of surface finish: organic and metallic. This article discusses a popular metal PCB surface treatment – gold-impregnated PCBS.

Understand 4-layer gold-plated PCB

The 4-layer PCB consists of 4 layers of FR4 substrate, 70 um gold and 0.5 OZ to 7.0 OZ thick copper substrate. The minimum hole size is 0.25mm and the minimum track/pitch is 4Mil.

Thin layers of gold were plated on nickel and then on to copper. Nickel acts as a diffusion barrier between copper and gold and prevents them from mixing. Gold dissolves during welding. Nickel is typically between 100 and 200 microinches thick and gold between 2 and 4 microinches thick.

Introduction to methods of gold plating on PCB

The coating is deposited on the surface of the FR4 material by a closely monitored chemical reaction. Furthermore, coating is applied after flux resistance is applied. In some cases, however, the coating is applied before welding, but this is very rare. This coating is more expensive than other types of metal coatings. Because the coating is done chemically, it is called chemical nickel leaching (ENIG).

Use of four layers of ENIG PCB

These PCBS are used in ball grid arrays (BGA) and surface mount devices (SMD). Gold is considered a good conductor of electricity. This is why many circuit assembly services tend to use this type of surface treatment for high-density circuits.

The advantages of surface treatment of sunken gold

The following advantages of gold-impregnated finishes make them very popular in electrical assembly services.

Frequent virtual plating is not required.

The reflux cycle is continuous.

Provide excellent electrical testing capability

Good adhesion

Provides horizontal plating around circuits and pads.

Submerged surfaces provide excellent flatness.

Can weld line.

Follow time-tested application methods.