Product Overview
FR4 (Flame Retardant 4) fiberglass board is a composite material made by laminating electronic-grade glass fabric impregnated with epoxy resin under high temperature and pressure. With excellent electrical insulation, mechanical strength and flame retardancy, it remains the classic substrate for communication equipment structures. In 5G base station AAUs (active antenna units), RRUs (remote radio units) and various RF test instruments, FR4 fiberglass board is widely used for antenna reflector supports, cavity insulation partitions, mounting backplates and test fixtures. Dongguan Chaorong Electronics Co., Ltd. supplies FR4 sheets in all thicknesses from 0.2 mm to 50 mm, with CNC precision machining, drilling, chamfering and surface grinding to meet the tight dimensional accuracy and consistency demands of communication equipment manufacturers.
Core Technical Features
1. Stable Dielectric Performance
At 1 MHz, FR4 exhibits a dielectric constant (εr) of 4.2–4.8, dissipation factor (tanδ) below 0.02, volume resistivity ≥10¹⁴ Ω·cm and surface resistivity ≥10¹³ Ω. These properties provide stable insulation and support for RF signal paths, avoiding signal degradation caused by dielectric loss. For Sub-6 GHz structural applications, these dielectric figures fully ensure electrical stability.
2. Multiple Glass Transition Temperature (Tg) Grades
Chaorong Electronics offers FR4 in standard Tg (130 °C), mid Tg (150 °C) and high Tg (170 °C) grades. The high-Tg version delivers better dimensional stability through reflow soldering and outdoor high-temperature environments, retaining interlaminar bond strength after damp-heat conditioning (moisture absorption <0.1%) — ideal for long-term outdoor base station operation.
3. High Mechanical Strength and Dimensional Stability
FR4 flexural strength reaches ≥340 MPa (lengthwise) / ≥280 MPa (crosswise) with compressive strength ≥400 MPa. The coefficient of thermal expansion (CTE) is approximately 13–17 ppm/°C in X/Y, effectively suppressing warpage after PCB mounting. Water absorption is ≤0.10%, and the material remains structurally stable through −40 °C to +130 °C cycling.
4. UL94 V-0 Flame Rating
The entire FR4 range meets the UL94 V-0 flammability standard — self-extinguishing and compliant with mandatory fire-safety requirements for communication equipment.
Typical Applications
5G Base Station Antenna Supports and Reflector Structures
In AAU antenna arrays, thin FR4 sheets (0.5 mm–2.0 mm) serve as radiator supports and isolation spacers, where low dielectric loss and flatness (warpage ≤0.5%) guarantee array consistency. Thick sheets (10 mm–20 mm) are used as mounting backplates and reflector cavity partitions.
RRU RF Cavity Insulation Partitions
Inside RRUs, cavities housing power dividers and filters require electrical isolation. CNC-machined custom-shaped FR4 partitions deliver over 2 kV withstand voltage while reducing overall weight. Common specifications are summarized below:
| Application | Recommended Thickness | Tg Grade | Key Requirements |
|---|---|---|---|
| Radiator support | 0.5–2.0 mm | 150 °C | Low warpage, high flatness |
| Cavity insulation partition | 3–8 mm | 170 °C | ≥2 kV withstand, CNC custom shapes |
| Mounting backplate | 10–20 mm | 150 °C | High rigidity, lightweight |
| RF test fixture | 5–12 mm | 130 °C | Dimensional stability, easy machining |
RF and Microwave Test Fixtures
In production-line RF testing, FR4 serves as the insulating baseplate and locating blocks of test tooling. Its stable dielectric constant minimizes the fixture's influence on S-parameter measurements and improves calibration consistency.
Selection Guide and Machining Recommendations
Defining Key Parameters
- Choose the Tg grade: select 170 °C high-Tg for outdoor or reflow environments; standard 130 °C suffices for indoor structural parts at lower cost.
- Define thickness and tolerance: structural load-bearing parts should be ≥3 mm; Chaorong's precision machining holds thickness tolerance within ±0.05 mm.
- Confirm flame retardancy and environmental compliance: complete units require UL94 V-0 plus RoHS and halogen-free certification — specify at ordering.
- Surface treatment: apply conformal coating or anodized edging where enhanced insulation is needed.
CNC Machining Recommendations
- FR4 contains glass fiber — diamond-coated tooling with moderate feed rates is recommended to minimize delamination.
- Thin sheets require vacuum-chuck fixturing to prevent warpage and hold hole-position accuracy within ±0.1 mm.
- For volume orders, perform first-article CMM inspection to confirm geometric tolerances before mass production.
Why Choose Dongguan Chaorong Electronics
Dongguan Chaorong Electronics Co., Ltd. has specialized in glass-fiber composite machining for years, operating multiple high-precision CNC machines and lamination inspection equipment. We provide build-to-print customization, volume precision machining and SGS material reports for FR4 sheets. With full raw-material traceability and 100% process inspection, we deliver stable, reliable insulation structural components for 5G communication equipment manufacturers — a dependable partner for building efficient communications infrastructure.