Background Theory > PCB Design > What are PCBs Made Of

PCBs (Printed Circuit Boards) are typically made of a combination of different materials that serve various purposes in the construction of the board. The main materials used in the manufacturing of PCBs are as follows:

Substrate Material

FR-4 (Flame Retardant 4): FR-4 is the most common substrate material used in rigid PCBs. It is composed of woven fiberglass cloth impregnated with epoxy resin. FR-4 provides good electrical insulation, mechanical strength, and dimensional stability. It is also flame retardant, making it safe for many applications.

Polyimide: Polyimide is a flexible substrate material used in flexible PCBs. It offers excellent flexibility and high-temperature resistance, making it suitable for applications where the PCB needs to bend or flex.

PT FE (Polytetrafluoroethylene): PT FE, commonly known by the brand name Teflon, is used in high-frequency applications and RF circuits due to its low dielectric constant and loss tangent. It is also known for its high-temperature stability.

Copper Foil

Copper is the primary conductor material in PCBs. Copper foil is bonded to the substrate material, and the conductive traces and pads are etched from this copper layer during the manufacturing process.

Solder Mask

Solder mask is a protective layer applied to the PCB to insulate the conductive traces and prevent solder bridges during assembly. It is typically green, but other colors like blue, red, black, and white are also used.

Silkscreen

The silkscreen layer includes markings and labels on the PCB, such as component outlines, reference designators, part numbers, and logos. It is printed in white or other contrasting colors for visibility.

Surface Finish

Surface finish is a coating applied to the exposed copper traces and pads to prevent oxidation and ensure good solderability during assembly. Common surface finish types include HASL (Hot Air Solder Leveling), ENIG (Electroless Nickel Immersion Gold), and OSP (Organic Solderability Preservative).

Solder Paste

Solder paste is used in surface-mount technology (SMT) assembly. It is a mixture of solder particles and flux that allows components to be temporarily held in place before reflow soldering.

Adhesive

In multilayer PCBs, an adhesive material is used to bond individual layers together before they are laminated and pressed to form a single board.

Prepreg

Prepreg is a resin-impregnated fiberglass material used between copper layers in multilayer PCBs. It helps to insulate and bond the layers together during the lamination process.

These materials are carefully selected based on the specific requirements of the PCB, such as its intended application, complexity, mechanical strength, thermal characteristics, and cost considerations. The combination of these materials and their arrangement determines the overall performance and functionality of the printed circuit board.