What Materials Are Commonly Used in Printed Circuit Board Assemblies?

Printed Circuit Board Assemblies

When you need to produce a printed circuit board, you must select the materials that will support your design and provide the necessary electrical and environmental properties. Your board’s function will dictate the number of layers, form factor and materials, but you must also consider the thermal and mechanical characteristics that will ensure your product will operate as intended in the device it will be placed in.

Choosing the right PCB materials for your project can significantly impact cost and performance. Understanding the various material options available will help you make an informed decision that can save money and time in both the design and production phases.

PCBs are typically made from a combination of rigid and flexible materials. The rigid part of the circuit board is called a substrate, and it holds the components and copper traces that conduct electricity. The flexible part of the printed circuit board assemblies is known as a core, and it can be made from either a non-conductive material or a metal. Some PCBs combine both rigid and flexible materials to create a hybrid circuit board that can be bent into different shapes, which is commonly known as a rigid-flex board.

What Materials Are Commonly Used in Printed Circuit Board Assemblies?

The base layer of the PCB is called a prepreg or pre-impregnated resin, and it forms the foundation for the rest of the structure. Between the core and the copper foil there may be several layers of prepreg sandwiched together with epoxy, which is then laminated to the copper foil. The core is then heat- and pressure-bonded to the copper foil using a hot melt epoxy. This process gives the PCB its physical strength and allows the layers of copper to be etched into their final shape.

There are a variety of dielectrics that can be used in a PCB, and each has its own set of insulating properties. Typical dielectrics include polytetrafluoroethylene (commonly known as Teflon), FR-4, FR-5, FR-6, and G-10. The selection of the right dielectric is based on the operating temperature, signal speed and other requirements of the circuit.

Some materials have better conductivity than others, and this is reflected in their cost. Choosing unnecessarily low-loss materials can increase the cost of a printed circuit board without a corresponding benefit.

Some circuit boards have complex designs that require a high-performance substrate. Examples of this include LED lighting products that must dissipate a lot of heat, or boards with high-speed digital components that need to operate over a wide temperature range. For these types of applications, a hard PCB constructed from aluminum is often used, as it offers superior performance, heat resistance and durability. For flexibility, some circuit boards are built from soft materials such as a polyimide or Kapton. These are more common in consumer electronics and can be shaped to fit into small form-factor devices. They also feature good chemical and temperature resistance, as well as a low coefficient of thermal expansion. In addition, soft PCBs are less likely to bend than conventional PCBs.