As the core component of electronic products, the selection of raw materials for a Printed Circuit Board (PCB) directly impacts the board's performance, reliability, and manufacturing costs.
The Core Determinant of Circuit Board Mechanical and Electrical Performance
The substrate serves as the backbone of a printed circuit board (PCB) and must possess essential properties such as electrical insulation, heat resistance, mechanical strength, and dimensional stability. Depending on the specific application scenario, substrates can be broadly categorized into two types: rigid substrates and flexible substrates.
Rigid Substrates: Glass fiber-reinforced epoxy resin (FR-4) constitutes the mainstream in this category; its composition includes epoxy resin, glass fiber cloth, and a curing agent. FR-4 boasts excellent electrical insulation properties (dielectric constant: 4.0–4.5), heat resistance (Tg value: 130–180°C), and mechanical strength (flexural strength: ≥300 MPa), making it widely utilized in fields such as consumer electronics and communication equipment. Furthermore, high-frequency substrates (such as PTFE and ceramic-filled substrates) are employed in high-frequency applications-such as 5G base stations and radar systems-due to their low dielectric loss (Df ≤ 0.002); however, their cost is 30% to 50% higher than that of FR-4.
Flexible Substrate: Centered on polyimide (PI) film, this material boasts heat resistance (with a long-term operating temperature range of -200°C to 300°C), flexibility (with a bending radius of ≤0.5 mm), and chemical stability that are significantly superior to those of traditional PET films; consequently, it serves as the preferred material for flexible printed circuit boards (FPCs). Although the cost of PI film is approximately two to three times that of FR-4, it effectively meets the requirements of dynamic bending applications, such as those found in wearable devices and automotive displays.
Conductive Materials: The Core Medium for Circuit Construction
Conductive materials must possess high conductivity, corrosion resistance, and processability; they are primarily categorized into two types: copper foil and conductive pastes.
Copper Foil: Accounting for approximately 30% to 40% of the total cost of a PCB, copper foil is classified by its manufacturing process into electrolytic copper foil (ED) and rolled copper foil (RA). Electrolytic copper foil features low surface roughness (Ra ≤ 0.5 μm), making it suitable for High-Density Interconnect (HDI) boards; rolled copper foil exhibits excellent ductility (elongation ≥ 15%) and is frequently utilized in flexible circuit boards. The thickness of the copper foil directly impacts its current-carrying capacity; standard thicknesses include 18 μm, 35 μm, and 70 μm, while high-frequency boards may employ ultra-thin copper foil (3–12 μm) to minimize signal loss.
Solder Mask Materials: Key to Circuit Protection and Enhanced Reliability
Solder mask materials must possess insulating properties, solder resistance, and chemical stability; they are primarily categorized into two types: liquid photosensitive inks and dry-film solder masks.
Liquid Photosensitive Ink: Cures under ultraviolet light to form a solder mask layer. It is characterized by high resolution (line width/spacing ≤ 50 μm) and strong adhesion (peel strength ≥ 1.5 N/mm), making it suitable for high-precision circuit boards. Its cost is approximately 80–120 RMB/kg; however, it requires accompanying exposure and developing equipment, which increases process complexity.
Dry Film Solder Mask: Utilizes a PET film as a carrier and forms the solder mask layer through thermal lamination followed by development. It offers simple operation (requiring no developing equipment) but features lower resolution (line width/spacing ≥ 100 μm) and is primarily used for low-density circuit boards.
