Materials Used in Circuit Board Construction

Circuit Board Construction

A circuit board is an electrical device built to hold and connect electronic components. The primary function of a circuit board is to route and transmit signals between components, but it can also perform other functions. In order for a circuit board to work properly, it must be constructed using the right materials. This is because different materials have varying properties that affect the overall functionality of a circuit board. Choosing the right materials can increase performance and lower manufacturing costs.

The main components of a circuit board are the insulating substrate, the copper layer and the solder mask layer. Depending on the type of circuit board, there may be other layers as well. The most common insulating material is fiberglass, or a glass fabric-reinforced epoxy laminate (commonly abbreviated to FR). Other insulating materials are cotton paper impregnated with phenolic resin, which comes in tan or brown; and specialized high-frequency materials based on polyimide or PTFE.

Conductive pathways are etched into the insulated substrates, or core material, to form the circuit boards. Thin layers of copper are laminated onto the core material to create these conducting paths, and holes for component insertion and the connections between these paths are drilled with computer-controlled machines. The holes are then plated with conductive copper to make them plated-through holes.

Materials Used in Circuit Board Construction

These holes allow signal connections to be made across multiple layers of the circuit board. The walls of these plated-through holes are often made conductive, and the resulting conductive pathways are called vias. The vias are used to connect the various layers of the circuit board, and they are typically sized to fit the dimensions of through-hole components.

Another important property of the PCB materials is the dielectric constant, which is the relative value of the material’s ability to conduct electricity. In most cases, the dielectric constant decreases with increasing frequency, which helps reduce signal distortion and ensure proper transmission of high-speed signals.

Other critical properties include track and hole resistance, and thermal expansion coefficients. Choosing materials with compatible thermal expansion characteristics minimizes mechanical stress during temperature fluctuations, and reduces the risk of damage to solder joints.

In addition, the operating environment must be taken into account when selecting the insulating materials for a circuit board. This includes factors such as temperature range, humidity, exposure to chemicals and outdoor elements, and vibration and shock.

The first layer of a circuit board is known as the substrate, and it consists of a reinforcing material such as fiberglass or a cellulose-based epoxy. A thin layer of copper is then laminated to this base, and a liquid polymer called soldermask is applied over the copper. The soldermask adds an insulating layer that protects the bare copper from oxidation and prevents solder bridges from forming between tightly-spaced pads.

The most common insulating substrate is FR-4, which is actually a fiberglass cloth bonded with a flame retardant epoxy. FR-4 is the most commonly-used material in PCBs because it’s inexpensive and relatively lightweight, but its insulating properties are limited. Other insulating materials are available for use in more demanding applications, such as metal-core and high-speed boards.

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