The Base Material Used in the Copper Foil of PCB

This Gold Phoenix PCB Knowledge Center article introduces the base materials used in the copper foil of PCBs, covering substrate, lamination, solder mask, silkscreen, copper thickness, and the role of copper.

Understanding the manufacturing pattern of a printed circuit board requires a step-by-step look at its structure. The fabrication of these boards involves different layers, explained in the following sequence.

Substrate Material

The base foundation over the fiberglass-reinforced plastic board is the substrate. A substrate is a dielectric structure of a sheet usually made up of epoxy resins and glass fiber. A substrate is designed in such a way that it can meet specific requirements, such as the glass transition temperature (Tg).

Lamination

As the name suggests, lamination is a process used to achieve required properties such as thermal expansion, shear strength, and glass transition temperature (Tg). Lamination is done under high pressure. Lamination and substrate together play a vital role in the flow of electrical charges in the PCB.

Silkscreen

The silkscreen is the text layer of the printed circuit board and is applied to the surface of the board. It consists of logos, numbers, and letters that help engineers and technicians understand the functionality and component placement of the circuit board.

Solder Mask

The solder mask defines the color of the printed circuit board. It is typically green, although other colors may also be used depending on design requirements. The color of the solder mask does not affect the functionality of the board.

Metal Foiling

For the flow of electrical charges, traces and pathways are created in printed circuit boards. These traces connect the components of the board and help electric charges and signals flow. Metal plays a significant role in the functionality of the board. For this purpose, copper is used in traces because of its high conductivity. Copper is also inexpensive and readily available.

The Thickness of Copper Foil

Greater copper thickness can increase current-carrying capacity, although thicker copper may also make etching more challenging. Generally, the copper foil thickness is expressed in ounces. One ounce of copper foil will cover one square foot of board area. Usually, the copper foil thickness in single-sided and double-sided printed boards is 1.4 mil (35 µm). Commonly used copper foil thicknesses in printed circuit boards include 18 µm, 35 µm, 55 µm, and 70 µm.

What Is the Role of Copper Foil in PCB?

Printed circuit boards are made up of many layers and components that include traces, silkscreen, metal layers, and other materials. Traces are the connecting elements of PCBs, because no charge flow can happen without traces. Traces provide electrical connections between components and are essential to the operation of most PCBs. Without PCBs, there is no concept of electronic devices. In the present age, every single device makes use of PCBs, and PCBs rely on copper more than other components because copper is essential for making traces.

The reason for using copper is its conductivity. The conductivity of copper ensures the flow of signals in the electronic device without interruption. Copper has high electrical conductivity because its metallic bonding structure allows electrons to move readily through the material. This is why copper can carry electric charges with minimal signal loss.

For making continuous metal foil, copper — a negative electrode material — is used on the first layer of PCBs. Due to the low level of surface oxidation, copper can be easily used with various types of substrates, metals, and insulating layers. Copper is used with a protective layer to form different circuit patterns after etching, because it can easily bond with the insulating layers of PCB. Copper foil can provide better continuity of electromagnetic shielding, which is why it is placed on the substrate sheet surface.