Types of PCB Material

fpsupdate

1 year ago

All circuit boards are built similarly, but there are many types of PCB material

Circuit boards are often classified according to the number of layers in the PCB stackup. For example, single-sided, double-sided, or multilayer are common terms used to distinguish between different board design types. Rigid, flex, and rigid-flex are also familiar distinctions.

PCBs are also segmented in terms of application or usage; such as high-speed or automotive. Far less common, but probably more important, is to distinguish between circuit boards based on their electrical, thermal, mechanical, and/or chemical characteristics. Knowing the parameters that quantify these important characteristics is essential for selecting the board with the types of PCB material that is best for your design.

Different Types of PCB Material

Believe it or not, FR4 is not the only PCB material type available. This may not be obvious, as many PCBA design programs default to this popular board type. However, the explosion of circuit board utilization into smart products, IoT devices, industrial production facilities, space platforms, and other applications, are forcing engineers and PCB designers to investigate other types of PCB material, as listed below, in order to meet specific quality requirements.

TYPES OF PCB MATERIAL
PCB Material Types	Characteristics
FR4	Most popular PCB material. Good general properties.
FR5	High coefficient of temperature expansion (CTE).
Polyimide	Great flexibility and good tensile strength.
Polytetrafluoroethylene (PTFE)	Have consistent dielectric constant (Dk) and low dissipation factor (Df).
Resin Coated Copper (RCC)	Special material with uncured resin and copper foil used in high-density interconnect PCBs.
Insulated Metal Substrate (IMS)	Metal based PCB with excellent thermal dissipation. Good dielectric strength at high voltages.

The list above is not exhaustive. However, the table clearly illustrates that PCB material properties can vary significantly. Your board’s operation, performance, durability, and reliability can be greatly impacted, if these attributes are not taken into account when selecting the type of PCB material for your design.

Choosing the Best Material for Your PCB

Knowing and understanding the parameters that specify PCB material properties is necessary to choose the best board material for your design, which is an important PCB layout best practice. This is done most effectively by grouping the parameters according to their area of impact. Below are the most important electrical, thermal, mechanical, and chemical parameters to know for the different types of PCB materials.

Important PCB Material Properties

Thermal Properties
- Coefficient of thermal expansion (CTE) – the rate at which the substrate expands due to heat.
- Decomposition temperature (Td) – the temperature above which the board will start to decompose.
- Glass transition temperature (Tg) – the temperature above which the board may not return to a stable hardened state once heat is removed.

Electrical Requirements
- Dissipation factor (Df) – a measure of how fast the board loses power.
- Dielectric constant (Dk) – a measure of how constant the board’s impedance is with respect to frequency changes.
- Electrical strength – a measure of resistance to breakdown in the board’s z-direction.
- Volume resistivity (𝛒) – the resistivity of a dielectric structure.
- Surface resistivity (𝛒S) – the resistivity along the surface of a dielectric structure.

Mechanical Requirements
- Tensile strength – a measure of how much pull or push stress a board can withstand before breaking.
- Flexural strength – an alternative measure of a board’s ability to withstand stress without breaking.
- Peel strength – a measure of how the copper stays attached to a dielectric in the presence of heat or chemical exposure.

Chemical Requirements
- Moisture absorption – a measure of the ability of a material to resist absorption when submerged in a liquid.
- Methylene chloride absorption (MCA) – a measure of the ability of a material to resist methylene chloride absorption.

If used effectively, the properties above can help you select the optimal type of PCB material to ensure your board not only achieves its functional and performance objectives, but also meets its quality requirements.

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