PCB Blog - What is gold plated PCB board?

What is gold plated? Gold plating is a type of PCB surface treatment, also known as nickel plating gold. In the PCB manufacturing process, it is achieved by depositing a layer of gold on the barrier layer of nickel through electroplating.And it can be divided into "hard gold plating" and "soft gold plating".

Gold plated PCB board

Gold-plated PCB boards are made by electroplating a layer of gold on the surface of PCB circuit board pads, which are made of hard gold. The principle is to dissolve nickel and gold in a chemical solution,immerse the circuit board in an electroplating cylinder, and connect an electric current to generate a nickel-gold coating on the copper foil of the circuit board.

The Role of Gold Plating

1.The two functions of gold plating are wear resistance and corrosion resistance.Parts with sockets and gold fingers need to be gold plated,and areas in contact with conductive rubber need to be gold plated. Circuit boards working in highly corrosive environments require the use of gold plated circuit boards.The circuit board is plated with gold to prevent oxidation, protecting the bottom layer of nickel and copper. The gold is wear-resistant and has good reliability.

2.The advantages of gold plated circuit boards are strong conductivity, good oxidation resistance, and long service life.The coating is dense and relatively wear-resistant,and is generally used in welding and socket applications.The gold plating process is widely used in circuit board components such as solder pads,gold fingers,connector shrapnel,and other positions.The most widely used hand circuit boards we use are mostly gold-plated boards.

3.Gold plating has low contact resistance,good conductivity, easy welding, strong corrosion resistance, and certain wear resistance (referring to hard gold), making it widely used in precision instruments, printed circuit boards, integrated circuits, tube shells, electrical contacts, and other fields.

The difference between soft gold and hard gold

In the PCB gold plating process, hard gold plating is also known as an electroplating alloy.It has been alloyed with other elements to make it harder,while soft gold plating is pure gold.

The application of electroplated gold in PCB manufacturing.Hard gold plating is suitable for areas such as gold fingers and keyboards that require friction.Soft gold is commonly used for aluminum or gold wiring on COB (on board chips).

Why use gold plated circuit boards

With the continuous improvement of integrated circuits, their pins show the development trend of high density and fine pitch. The traditional vertical tin spraying process in the face of the refined pad processing has been apparent inability:on the one hand, it is difficult to ensure that the pad surface is absolutely flat, which directly affects the surface mount technology (SMT) paste printing accuracy and reflow soldering quality; on the other hand, there are oxidation hazards of tin spraying boards, resulting in the unused state of the storage life (shelf life) is significantly limited. The emergence of the gold plating process has effectively addressed these challenges:

Process Adaptability Advantages

In high-density assembly scenarios, especially for ultra-miniature packages such as 0402, 0201, etc., the flatness of the pad surface directly determines the uniformity of solder paste printing and solder reliability. The whole-board gold-plating process forms a dense gold layer through chemical deposition, which is perfectly adapted to ultra-fine line width/space designs of 3-4mil, providing ideal basic conditions for high-density mounting.

Storage Time Advantage

PCBs are often stored for weeks to months during the R&D pilot phase due to component supply cycles.The excellent oxidation resistance of gold plated surfaces increases storage life by several times that of traditional tin-sprayed boards, and the cost per batch in the pilot phase is comparable to that of traditional processes, making it the preferred option in the R&D validation phase.

However, as the wiring density evolves to the 3-4 mil level, new technical contradictions begin to come to the fore:

Signal integrity risk due to skin effect

When the signal frequency into the high-frequency field (such as 5GHz or more), the current will show obvious skin effect - that is, the current density to the surface of the conductor to concentrate, the effective transmission cross-sectional area is reduced. For precision circuits with multi-layer gold-plated structures, this effect can lead to:

Changes in the equivalent impedance of the signal transmission path

Increased coupling capacitance between signals across layers

Increased attenuation of high frequency signals

The above problems are particularly significant in high-frequency, high-speed digital signal transmission, and have become technical bottlenecks that limit the evolution of the gold-plating process to more advanced processes.

The Difference between PCB Gold Deposition and Plating

1.Process principle

PCB gold deposition is a process of depositing metal ions on the surface of a circuit board. During this process,the circuit board is immersed in a solution containing gold salts and reducing agents,and gold ions are reduced to metal and deposited on the surface of the circuit board. Gold plating is the process of immersing a circuit board in a solution containing gold salts, and then applying electricity to deposit gold ions on the surface of the circuit board.

2.Metal thickness

The metal thickness of PCB sinking gold and plating gold is different.Gold deposition can form a relatively thick metal layer,typically reaching 2-5 microns.The gold plated metal layer is relatively-thin,usually only around 0.5-1.5 microns.

3.Metal color

The metal colors of PCB sinking gold and gilding are also different.The metal color of heavy gold is golden yellow,while the metal color of gilding is light yellow.

4.Surface flatness

The surface flatness of PCB sinking gold and gold plating is also different.The surface of the sinking gold is relatively flat,which can maintain high-quality welding and contract performance. 

The surface of gold plated is relatively rough,which is prone to welding and contact problems.

5.Cost

The cost of PCB gold deposition and plating is also different.The cost of sinking gold is relatively high because it requires more chemical reagents and a longer processing time.The cost of gold plating is relatively low because of its short processing time and simple operation.

Process flow of PCB gold plating

Gold plating has low contact resistance, good conductivity, easy welding, strong corrosion resistance,and certain wear resistance (referring to hard gold),making it widely used in precision instruments,printed circuit boards,integrated circuits,tube shells,electrical contacts,and other fields.

1.Surface treatment:Clean the surface of the PCB to remove oil stains,burrs,oxide layers, etc.

2.Electroplating:Place the PCB into the electroplating bath and add the plating solution.The electroplating solution contains a reducing agent,which can reduce the gold atoms on the PCB surface into metal ions and deposit them on the PCB surface.

3.Water washing:After electroplating,there will be a layer of metal deposition on the surface of the PCB, which needs to be cleaned with water.

4.Drying:Place the PCB in a drying oven and dry with water.

5.Adhesive application:Apply a layer of conductive adhesive to the surface of the PCB to ensure good contact between the PCB and other devices.

6.Recycling:Remove the PCB from the adhesive tape and place it in the recycling bin.

The gold plated PCB board can play a protective role,and the gold-plated layer can protect the circuit board from oxidation,corrosion,and other effects,increasing the service life of the circuit board.Metals themselves have good conductivity,which can improve the conductivity of PCBs and reduce line impedance.