Core Applications and Development Trends of Epoxy Resins in PCB Substrates

Epoxy resins play a critical role in the manufacturing of printed circuit boards (PCB), serving as one of the core materials for PCB substrates due to their excellent insulation properties, mechanical strength, and chemical stability. The following sections detail the applications and characteristics of epoxy resins in PCB from multiple perspectives:

Core Applications of Epoxy Resins in PCB Substrates

The primary application of epoxy resins is in PCB substrates (copper-clad laminates, CCL), which typically feature a composite structure of "resin + reinforcing material + copper foil":

• Combination with Reinforcing Materials

Epoxy resins are often combined with glass fiber cloth (a core component of FR-4 substrates) to form a high-strength, highly insulating substrate after curing. The glass fiber cloth provides mechanical support, while the epoxy resin binds the fibers through impregnation and curing, resulting in a stable composite structure.

• Insulation and Bonding Functions

In copper-clad laminates, epoxy resins like specialty epoxy resins not only act as an insulating layer to isolate copper circuits but also bond the copper foil to the substrate, ensuring the foil remains intact during processing (e.g., etching, drilling) and use.

Key Properties and Advantages of Epoxy Resins in PCBs

1、Excellent Electrical Insulation
Cured epoxy resins exhibit a stable molecular structure, with low dielectric constant (ε) and dissipation factor (tanδ), effectively reducing signal loss and interference. This makes them particularly suitable for high-frequency PCBs (e.g., 5G communication and radar equipment).

2、Superior Mechanical Properties
Cured epoxy resins offer high tensile and flexural strength, enabling them to withstand mechanical stresses during PCB processing (e.g., cutting, drilling) and use. When combined with glass fiber cloth, the substrate’s dimensional stability is significantly enhanced, reducing warping caused by temperature changes (low coefficient of thermal expansion, CTE).

3、Chemical and Thermal Resistance
Epoxy resins resist corrosion from acids, alkalis, and solvents, making them durable against etching solutions and cleaning agents used in PCB manufacturing. The glass transition temperature (Tg) is a key indicator: standard FR-4 substrates have a Tg of approximately 130–150°C, while high-Tg variants (e.g., above 170°C) meet the requirements of high-temperature soldering (e.g., lead-free soldering, with a melting point of about 217°C) and harsh environments.

4、Process Adaptability
Epoxy resins exhibit good fluidity before curing, allowing them to uniformly impregnate glass fiber cloth and ensure a homogeneous substrate structure. The curing process can be controlled by adjusting temperature and time, making it suitable for large-scale industrial production (e.g., lamination processes for CCL).

Types of Epoxy-Based PCB Substrates

Depending on performance requirements, epoxy resins from tetra material can be combined with other materials to form different types of substrates:

• FR-4

The most commonly used substrate, comprising epoxy resin and glass fiber cloth, with a UL94 V-0 flame retardancy rating. It is widely used in consumer electronics (e.g., computers, smartphones).

• High-Tg FR-4

Features an optimized epoxy resin formulation (e.g., with modifiers) to increase Tg and enhance thermal resistance. It is used in automotive electronics, industrial controls, and other high-temperature applications.

• High-Frequency Epoxy Substrates

Designed to reduce dielectric constant (e.g., by introducing fluorine or low-polarity groups) and minimize high-frequency signal loss. These substrates are suitable for communication equipment (e.g., base stations, satellite antennas).

• Flame-Retardant Epoxy Substrates

Incorporate flame retardants (e.g., brominated epoxy resins) to meet PCB flame retardancy requirements and prevent fire risks caused by short circuits.

Other Applications of Epoxy Resins in PCB

Beyond substrates, epoxy resins are also used in other aspects of PCB manufacturing:

• Solder Mask Inks

Some solder mask inks are based on epoxy resins, which form an insulating protective layer after curing to prevent pad oxidation and circuit shorting.

• Adhesives

Epoxy resins serve as interlayer bonding materials in the lamination process of multilayer PCB, ensuring strong adhesion between substrate layers.

• Potting and Sealing

Epoxy potting compounds protect PCB components from moisture, dust, and mechanical shock.

Development Trends of Epoxy Resins in the PCB Field

As electronic devices evolve toward miniaturization, high-frequency operation, and enhanced reliability, epoxy resins based on specialty resin and chemical solutions are also being continuously improved:

• Low Dielectric Loss

Development of epoxy resins suitable for millimeter-wave frequencies (e.g., 6G) to reduce signal transmission loss.

• Higher Thermal Resistance

Increasing Tg to above 200°C to meet the demands of extreme environments, such as automotive electronics and aerospace applications.

• Eco-Friendly Formulations

Reducing the use of brominated flame retardants and developing halogen-free epoxy resins (e.g., phosphorus-based retardants) to comply with environmental standards like RoHS.