FPC Plating

In the manufacturing of flexible printed circuit boards (Flexible PCBs), plating is a critical process used to ensure electrical conductivity and to protect the circuitry.
This page explains various plating techniques used in Flexible PCBs, including electroplating.

What Is Plating in Flexible PCBs?

Plating to Deposit a Conductor Layer on the Substrate

To form a copper layer on the base insulating material, electroless plating is used to deposit a conductive seed layer onto the surface.

Electroless nickel plating is commonly adopted for creating this seed layer.

Plating to form circuits

To form the actual circuits, both electrolytic copper plating and electroless copper plating are used.

Through Hole Plating

Through-hole plating is used in multilayer flexible PCBs, such as those with two or more layers. It involves drilling holes to establish electrical connections between conductor layers, and then plating the inner walls of the holes.

After securing conductivity inside the holes with electroless copper plating, electrolytic copper plating is applied.

Plating for surface treatment

Various types of plating are used for terminal surface finishing.

Common methods include electrolytic nickel-gold plating, electroless nickel-gold plating, tin plating, and solder plating.The following is a list of the most important factors that can be considered.

Differences Between Plating Methods

Electroless Plating

Electroless plating is a process that deposits metal onto the conductive surface of a Flexible PCB using a chemical reaction in the plating solution.

Common metals used include copper, nickel, and gold. Compared to sputtering, electroless plating can be performed in ambient conditions, which increases productivity. Additionally, since no electrodes are required as in electrolytic plating, it allows for uniform film thickness with greater ease.

However, it requires pretreatment and strict control of the plating solution to ensure proper chemical reactions and high-quality plating layers. Proper waste disposal must also be considered.

Electroless Copper Plating

Plating for circuit formation and through-hole platingUsed in circuit formation and through-hole plating processes.

Electroless Nickel Plating (ENP)

Applied over a nickel layer during surface finishing. It can also be applied directly in some cases.
This type of gold plating provides excellent solderability.

Electroless Gold Plating

Commonly used as plating applied over nickel in plating for surface treatment. There is also a method of directly applying gold plating.. This type of gold plating provides excellent solderability.
It is characterized by good solder wettability.

Electrolytic Copper Plating

In electrolytic plating, the Flexible PCB acts as the cathode, while a metal or insoluble electrode acts as the anode. When current is applied, metal is deposited on the conductive surface of the PCB.

Common metals include copper, nickel, tin, and solder. This method allows for easy control of film thickness and quick processing, although achieving uniformity across the entire surface may require additional steps.

Electrolytic Copper Plating

Plating to form circuitsUsed in circuit formation and through-hole plating.Through Hole PlatingThe following is used for

Electrolytic Nickel Plating

Plating for surface treatmentUsed in surface finishing as a base for gold plating.

Electrolytic gold plating

Plating for surface treatmentAlso used in surface finishing, applied over nickel layers.

Compared to electroless gold plating, the gold layer is thicker, making it suitable for applications that require durability and frequent mating/unmating cycles. It offers excellent performance but comes with higher cost.

Electrolytic Solder Plating

Joints with other substrates, etc.Commonly used at interconnection points with other boards.

Summary

There are many different types of plating, and the metal types introduced here are among the most commonly used in Flexible PCB manufacturing.

Because there are numerous combinations of plating methods and metal types, it is advisable to communicate your required specifications and intended applications to the manufacturer for optimal recommendations.

See the List of Manufacturers
Handling Flexible PCBs