Basic Components of a Circuit Board

PCBsupplierChina talk a circuit board comprises several key components, each serving a specific function in the overall operation of the electronic device. These components include conductive pathways, substrate material, solder mask, and silkscreen.

Conductive Pathways
Conductive pathways, often called traces, are thin lines of conductive material, typically copper, that are etched onto the surface of the circuit board. These are highly conductive tracks etched on the circuit board to serve as wiring, allowing electrical signals to travel between the various components mounted on the board.

Fig 1: Circuit traces connecting various components on a bare board

Substrate Material
The substrate, often referred to as the base material, is the solid, non-conductive foundation upon which the other components of a circuit board are built. It provides mechanical strength to the board and acts as an electrical insulator between the layers of conductive material.

The most commonly used substrate for circuit boards is a glass-reinforced epoxy laminate known as FR-4 (Flame Retardant type 4). This material is chosen for its desirable properties:

Good strength-to-weight ratio

Low cost

Excellent electrical insulation.

The "FR" in FR-4 indicates that the material is flame retardant, a critical safety feature for electronic devices.

These materials can be used for circuits for up to 7GHz. The preferred substrate materials for higher frequencies are Polyamide, Ceramics, and Metal-core substrates.

Polyimide is often used in flexible circuit boards due to its flexibility and heat resistance.

Due to their superior electrical and thermal properties, ceramic substrates are used in high-frequency and high-power applications.

Metal-core substrates typically consist of an aluminium core with a non-conductive dielectric layer. They are used in LED lighting applications for their excellent heat dissipation capabilities.

A Flexible PCB（FPC）

Solder Mask
The solder mask is a critical circuit board component that serves multiple functions. It is a thin layer of polymer material applied over the copper traces and vias of the circuit board, leaving only the areas to be soldered exposed. This layer is typically green but can also be in other colours, such as blue, red, or black.

The primary function of the solder mask is to prevent solder bridges from forming between closely spaced solder pads during the soldering process. Solder bridges can create short circuits, which can cause the electronic device to malfunction or even fail. By covering the copper traces and vias, the solder mask ensures that the solder flows only onto the exposed solder pads and not onto the traces.

Solder mask and exposed conductive pads

Silkscreen
The silkscreen provides important information about the board and its components.    It is a layer of ink printed onto the circuit board's surface, typically on top of the solder mask.    The silkscreen contains various markings, such as component designators, reference designators, logos, and other text or symbols that aid in the electronic device's assembly, testing, and troubleshooting.

Component designators are labels that identify the type of component, such as "R" for resistors, "C" for capacitors, and "Q" for transistors.    Reference designators are unique identifiers assigned to each component on the board, allowing for easy identification and location of specific components during assembly and troubleshooting.    For example, a resistor might be labelled "R1," while a capacitor might be labelled "C1."

Fig 4: A typical PCB silk screen

PCBmanufacturer talk the silkscreen is typically applied using a screen printing process similar to the solder mask. A stencil or screen with the desired pattern is placed over the circuit board, and ink is forced through the openings onto the board's surface.