Overview of PCB Materials
Printed Circuit Boards (PCBs) are fabricated using various materials to meet specific performance and application requirements. In China, PCB copper-clad laminates (CCLs) are extensively used, and they can be categorized by base materials, resin adhesives, flame retardancy, and performance levels.
Types of Copper-Clad Laminates (CCLs)
1. Classification by Reinforcement Material
- Paper-based materials: Typically used for low-cost and low-performance applications.
- Glass fiber cloth-based materials: Preferred for high-performance needs due to their durability and electrical properties.
- Composite bases (CEM series): Combine the benefits of paper and fiberglass bases.
- Special materials: Ceramic and metal-core bases for unique applications like high-heat dissipation.
2. Classification by Resin Adhesive
- Phenolic resin (XPc, XxxPC, FR-1, FR-2): Economical but limited in performance.
- Epoxy resin (FE-3, FR-4, FR-5): Most commonly used for general and high-performance PCBs.
- Polyester resin: Provides moderate performance.
- High-performance resins:
- Bismaleimide triazine (BT) for high-temperature stability.
- Polyimide (PI) for excellent heat resistance.
- Diphenylene ether (PPO) for low dielectric constant applications.
Flame Retardancy of CCLs
CCLs are classified based on their flame retardant properties:
- Flame-retardant (UL94-V0, UL94-V1): Resists ignition and limits flame spread.
- Non-flame retardant (UL94-HB): Burns slowly, suitable for low-risk applications.
- Green flame retardant: Bromine-free for environmentally safe products.
Performance-Based Classification
- General performance: Standard FR-4 boards for most applications.
- High heat resistance: Tg (glass transition temperature) above 150°C.
- Low dielectric constant: For high-frequency circuits.
- Low thermal expansion: Used in packaging substrates.
PCB Material Standards
1. National Standards
- China: GB/T4721-4722-1992 and GB4723-4725-1992.
- Taiwan: CNS standard based on JIS.
2. International Standards
- JIS (Japan), ASTM, IPC, ANSI, UL (USA), DIN (Germany), IEC (International), among others.
Detailed Parameters and Uses of Common Materials
| Material Type | Description | Applications |
|---|---|---|
| 94HB | Non-flame retardant, low-cost cardboard. | Simple electronics, non-critical. |
| 94V0 | Flame-retardant cardboard. | Basic electronics, consumer products. |
| CEM-1 | Single-sided fiberglass board. | Cost-effective single-sided PCBs. |
| CEM-3 | Double-sided semi-fiberglass board. | Low-end double-sided applications. |
| FR-4 | High-performance fiberglass board. | Multi-layer, high-reliability PCBs. |
Key PCB Material Parameters
- Flame Retardancy: Ranges from 94V-0 (highest) to 94HB (lowest).
- Prepreg Thickness:
- 1080 = 0.0712 mm
- 2116 = 0.1143 mm
- 7628 = 0.1778 mm
- Tg (Glass Transition Temperature):
- General: ≥130°C
- High Tg: ≥170°C
- Medium Tg: ≥150°C
- Halogen-Free Materials: Environmentally friendly, eliminates toxic halogens.
- High Tg Benefits:
- Superior heat resistance.
- Enhanced stability and durability.
- Ideal for high-functionality and multi-layer designs.
Differences Between Standard FR-4 and High Tg Materials
| Property | FR-4 | High Tg |
|---|---|---|
| Heat Resistance | Moderate | Excellent |
| Moisture Resistance | Standard | Improved |
| Thermal Decomposition | Occurs at lower temperatures | Delayed significantly |
| Applications | Standard electronics | High-performance, lead-free soldering |
Understanding the classification and parameters of PCB materials is essential for selecting the right material for a specific application. Factors like flame retardancy, Tg, resin type, and base material play critical roles in the performance and reliability of PCBs.
