FR Raw Material: Why Is It the First Choice for Electronic Components? How Does FR4 Balance Flame Retardancy and Insulation?

1. What Advantages Make FR Raw Material the Preferred Choice for Electronic Components?

FR (Flame Retardant) raw materials have become the core material for electronic components due to their unique combination of performance, safety, and adaptability—addressing the key pain points of electronic systems such as fire risk, signal stability, and environmental resistance.

Inherent Flame Retardancy: Eliminating Fire Hazards in Confined Spaces

Electronic components (such as circuit boards, connectors) are often used in dense layouts (e.g., server cabinets, automotive electronic control units), where a single component fire can trigger a chain reaction. FR raw materials are designed to resist combustion: they either self-extinguish within 10 seconds after leaving the fire source (meeting the UL94 V-0 flame retardant standard) or do not produce dripping molten materials (avoiding secondary ignition). Unlike non-flame retardant materials (such as ordinary epoxy resin), which burn continuously and release toxic gases (e.g., carbon monoxide, hydrogen chloride) when heated, FR materials can reduce the fire spread rate by 80% in case of a short circuit or overload—critical for protecting expensive electronic equipment and ensuring personnel safety.

Stable Insulation Performance: Guaranteeing Signal Transmission Accuracy

Electronic components rely on insulation materials to prevent current leakage and signal interference. FR raw materials have excellent dielectric properties: their volume resistivity is usually ≥10¹⁴ Ω·cm (100 times higher than that of non-FR insulating materials), and the dielectric loss tangent (tanδ) is ≤0.02 at 1MHz. This means they can maintain stable insulation even in high-frequency signal environments (e.g., 5G base station components, aerospace electronic devices), avoiding signal attenuation or crosstalk. For example, in a high-speed circuit board, FR materials ensure that the voltage drop between adjacent circuits is less than 0.1V, meeting the precision requirements of electronic signal transmission.

Environmental Adaptability: Withstanding Harsh Working Conditions

Electronic components operate in diverse environments—from high-temperature automotive engine compartments (ambient temperature up to 125℃) to humid outdoor communication cabinets (relative humidity >95%). FR raw materials have strong environmental resistance:

• High-temperature resistance: Most FR materials can maintain structural stability at 130-180℃, with glass transition temperature (Tg) ≥130℃ (Tg refers to the temperature at which the material transitions from a rigid state to a flexible state). For example, in automotive electronic control modules, FR materials do not soften or deform even when the engine temperature rises to 150℃.

• Moisture resistance: FR materials have low water absorption (≤0.15% after 24 hours of immersion in 23℃ water), preventing insulation performance degradation caused by moisture absorption. In coastal areas with high humidity, FR-based circuit boards can maintain normal operation for more than 5 years without leakage.

• Chemical resistance: They are resistant to common industrial chemicals (e.g., engine oil, cleaning agents) and do not react with these substances to produce harmful by-products—ensuring long-term reliability in automotive, industrial control, and other fields.
  
  

Cost-Effectiveness: Balancing Performance and Budget

While FR raw materials are slightly more expensive than non-flame retardant materials (cost increase of 10%-20%), their comprehensive cost advantage is obvious. First, they reduce the need for additional fire protection measures (such as installing fire barriers in electronic cabinets), saving 30%-40% of auxiliary material costs. Second, their long service life (5-10 years, twice that of non-FR materials) reduces the frequency of component replacement and maintenance. For example, in a large data center, using FR-based circuit boards can reduce maintenance costs by 25% over 5 years compared to non-FR alternatives.

2. What Is FR4 Material? Why Is It the Most Widely Used FR Raw Material in Electronic Components?

FR4 is a type of glass fiber-reinforced epoxy resin composite material, and its name comes from the NEMA (National Electrical Manufacturers Association) standard—"FR" represents flame retardant, and "4" indicates the fourth type of flame retardant material. It has become the most mainstream FR raw material in the electronic component industry due to its balanced performance and mature manufacturing process.

Composition of FR4: The "Three-Core" Structure Determines Performance

FR4 is composed of three key parts, each contributing to its overall performance:

• Reinforcement layer: Made of glass fiber cloth (usually E-glass fiber), which provides structural strength. The glass fiber cloth has high tensile strength (≥3000MPa) and low thermal expansion coefficient (≤15×10⁻⁶/℃), ensuring that FR4 does not warp or deform during processing (e.g., circuit board drilling, soldering).

• Matrix resin: Epoxy resin modified with flame retardant additives (e.g., brominated epoxy resin, phosphorus-based flame retardants). The resin binds the glass fiber cloth into a whole and provides insulation and flame retardancy.

• Filler: Optional components such as silica powder, which can adjust the material's thermal conductivity and dimensional stability. For high-power electronic components (e.g., LED drivers), adding high thermal conductivity fillers can improve heat dissipation efficiency by 20%-30%.
  
  

Performance Advantages of FR4: Meeting the Multi-Dimensional Needs of Electronic Components

Compared with other FR materials (such as FR1, FR2), FR4 has obvious comprehensive advantages:

• Higher mechanical strength: Its flexural strength is ≥450MPa (30% higher than FR2), making it suitable for load-bearing electronic components (e.g., printed circuit boards for industrial robots, which need to withstand mechanical vibration).

• Wider temperature adaptation range: The continuous use temperature of FR4 is 130-150℃, and the short-term resistance temperature can reach 260℃ (meeting the lead-free soldering temperature requirements of electronic components). In contrast, FR1 can only be used below 105℃, limiting its application in high-temperature environments.

• Better processability: FR4 can be processed into thin sheets (minimum thickness 0.1mm) or thick plates (maximum thickness 50mm) and supports precision operations such as laser drilling (hole diameter ≥0.1mm) and surface mounting—adapting to the miniaturization and high-density trends of electronic components.
  
  

Application Scope of FR4: Covering the Entire Electronic Industry Chain

FR4 is widely used in almost all types of electronic components:

• Printed Circuit Boards (PCBs): The core material of single-sided, double-sided, and multi-layer PCBs, accounting for 90% of the raw material consumption of rigid PCBs.

• Electronic Enclosures: Used to manufacture insulating enclosures for power supplies, connectors, and sensors—preventing electric shock and electromagnetic interference.

• Insulating Spacers: In high-voltage electronic components (e.g., transformers, inverters), FR4 spacers are used to isolate different voltage levels, ensuring insulation safety.

• Heat Sinks: Modified FR4 with high thermal conductivity (thermal conductivity ≥1.5W/(m·K)) is used as a heat dissipation substrate for LED chips and power semiconductors, replacing traditional metal heat sinks in some scenarios to reduce weight.
  
  

3. How Does FR4 Balance Flame Retardancy and Insulation? The Core lies in Material Formula and Process Control

Flame retardancy and insulation are sometimes mutually restrictive—some flame retardant additives may reduce the insulation performance of the material. FR4 solves this contradiction through precise formula design and strict process control, achieving "double excellence" in both properties.

Formula Design: Selecting Flame Retardant Additives That Do Not Affect Insulation

The key to balancing flame retardancy and insulation lies in choosing the right flame retardant additives and controlling their dosage:

• Brominated Flame Retardants (BFRs): Traditional FR4 uses brominated epoxy resin as the matrix, where bromine atoms can capture free radicals generated during combustion (inhibiting the chain reaction of combustion) and form a dense carbon layer on the material surface (blocking oxygen and heat transfer). Brominated flame retardants have high efficiency (adding 15%-20% can meet UL94 V-0 standard) and good compatibility with epoxy resin—they do not destroy the resin's molecular structure, so the insulation performance of FR4 is barely affected (volume resistivity remains ≥10¹⁴ Ω·cm).

• Phosphorus-Based Flame Retardants (Non-BFRs): For environmentally friendly requirements (e.g., RoHS 2.0 standard), phosphorus-based flame retardants (such as red phosphorus, phosphate esters) are used instead of brominated ones. Phosphorus-based flame retardants work by generating phosphoric acid during combustion, which promotes the material to form a carbon layer and releases non-flammable gases (e.g., nitrogen) to dilute oxygen. To avoid phosphorus-based additives reducing insulation, manufacturers use "micro-encapsulation technology"—coating phosphorus-based particles with a thin layer of epoxy resin, which isolates the flame retardant from the insulation matrix and ensures the volume resistivity of FR4 is still ≥10¹³ Ω·cm (meeting the insulation requirements of most electronic components).

• Synergistic Flame Retardancy: By combining two or more flame retardants (e.g., bromine + antimony trioxide), the flame retardant efficiency is improved while reducing the total additive dosage. For example, adding 12% brominated resin + 3% antimony trioxide can achieve the same flame retardant effect as adding 20% brominated resin alone—less additive means less impact on insulation performance.
  
  

Process Control: Ensuring Uniformity of Material Structure to Avoid Insulation Weak Points

Even with a reasonable formula, improper processing can lead to uneven distribution of flame retardants or defects in the material structure, resulting in local insulation degradation. FR4 manufacturing strictly controls the following processes:

• Glass Fiber Impregnation: The glass fiber cloth is fully impregnated with flame retardant epoxy resin, and the impregnation speed (1-2m/min) and resin viscosity (500-800cP) are controlled to ensure that the resin penetrates every fiber gap. This avoids "dry spots" (areas without resin) in the material—dry spots have poor insulation and are prone to ignition.

• Hot Pressing Forming: The impregnated glass fiber cloth is pressed into sheets at high temperature (160-180℃) and high pressure (20-30MPa). The hot pressing time (30-60 minutes) is adjusted according to the thickness of the sheet to ensure that the resin is fully cured and the flame retardants are evenly distributed. Over-curing will make the material brittle (reducing mechanical strength), while under-curing will leave unreacted resin (reducing both flame retardancy and insulation).

• Surface Treatment: After forming, the FR4 sheet is polished to remove surface defects (e.g., burrs, resin nodules). These defects are easy to accumulate dust and moisture, which will reduce the surface insulation resistance. The polished surface has a roughness (Ra) ≤0.8μm, ensuring stable insulation performance.
  
  

Performance Verification: Dual Testing of Flame Retardancy and Insulation

To ensure that FR4 meets both performance requirements, manufacturers conduct strict testing before leaving the factory:

• Flame Retardancy Test: According to UL94 standard, the FR4 sample (127mm×12.7mm×3.2mm) is vertically burned with a 10mm flame for 10 seconds, then the flame is removed. If the sample self-extinguishes within 10 seconds and no molten material drips, it meets the V-0 standard.

• Insulation Test:

• • Volume Resistivity Test: Measure the resistance between two electrodes in the material (applied voltage 500V DC), requiring ≥10¹³ Ω·cm.

• • Dielectric Strength Test: Apply AC voltage (50Hz) to the FR4 sample until breakdown occurs, requiring the dielectric strength ≥20kV/mm (ensuring no breakdown in high-voltage electronic components).

• • Tracking Index Test (CTI): Measure the voltage at which the material surface forms a conductive path under the action of a solution (0.1% ammonium chloride solution), requiring CTI ≥175V (avoiding surface leakage caused by moisture and dust).
    
    

4. What Factors Should Be Considered When Selecting FR4 for Different Electronic Component Scenarios?

Not all FR4 materials are the same—different grades of FR4 have differences in flame retardancy, insulation, and temperature resistance. Selection must be based on the specific requirements of electronic components.

Selection Based on Flame Retardant Level: From Basic Protection to High Safety

FR4 has different flame retardant grades according to UL94 standards, and the selection depends on the fire risk of the application scenario:

• UL94 V-2 Grade: Suitable for low-risk scenarios (e.g., household electronic appliances with low power, such as remote controls). The sample self-extinguishes within 30 seconds after leaving the fire, and molten material can drip (but does not ignite the cotton below).

• UL94 V-1 Grade: For medium-risk scenarios (e.g., office equipment such as printers). The sample self-extinguishes within 30 seconds, and no molten material drips.

• UL94 V-0 Grade: For high-risk scenarios (e.g., server circuit boards, automotive engine compartment components). The sample self-extinguishes within 10 seconds, and no molten material drips—this is the most widely used grade of FR4.

• UL94 5VA Grade: For extreme-risk scenarios (e.g., aerospace electronic components). The sample is burned with a 50mm flame for 5 seconds, self-extinguishes within 60 seconds, and no holes are formed (higher flame retardant requirements than V-0).
  
  

Selection Based on Insulation Performance: Adapting to High-Frequency and High-Voltage Environments

For electronic components with strict insulation requirements, higher-grade FR4 should be selected:

• General Insulation Requirements (e.g., low-frequency circuit boards): Ordinary FR4 (volume resistivity ≥10¹⁴ Ω·cm, dielectric strength ≥20kV/mm) is sufficient.

• High-Frequency Environments (e.g., 5G antenna components): High-frequency FR4 with low dielectric loss (tanδ ≤0.015 at 10GHz) is required. This type of FR4 uses low-loss epoxy resin and high-purity glass fiber cloth, avoiding signal attenuation caused by high dielectric loss.

• High-Voltage Environments (e.g., power supply transformers): High-voltage FR4 with dielectric strength ≥30kV/mm is selected. The material has fewer internal defects (e.g., bubbles, impurities) to prevent breakdown under high voltage.
  
  

Selection Based on Temperature Resistance: Matching the Operating Temperature of Components

The glass transition temperature (Tg) of FR4 determines its high-temperature application range:

• Low Tg FR4 (Tg = 130-150℃): Suitable for normal-temperature environments (e.g., household electronic components, office equipment), where the operating temperature does not exceed 100℃.

• Medium Tg FR4 (Tg = 150-170℃): For medium-temperature environments (e.g., automotive on-board electronic components, industrial control systems), where the operating temperature is 100-125℃.

• High Tg FR4 (Tg ≥170℃): For high-temperature environments (e.g., engine compartment components, LED high-power lamps), where the operating temperature is 125-150℃. High Tg FR4 uses modified epoxy resin (e.g., novolac epoxy resin) to improve the glass transition temperature.
  
  

5. What Common Misunderstandings Should Be Avoided When Using FR4 Material?

Misunderstanding 1: "FR4 Is Non-Flammable"

FR4 is "flame retardant" rather than "non-flammable". It can self-extinguish after leaving the fire source but will still burn when continuously exposed to high-temperature flames (e.g., a 1000℃ acetylene flame). Therefore, in extreme fire scenarios (e.g., large-scale circuit short circuits), additional fire protection measures (such as fire-resistant cables, fire extinguishing systems) are still required, and FR4 cannot be relied on alone for fire prevention.

Misunderstanding 2: "Higher Flame Retardant Grade Means Better Performance"

Blindly pursuing high flame retardant grades (e.g., using UL94 5VA grade FR4 for ordinary household remote controls) is unnecessary and increases costs. The 5VA grade FR4 is 30%-50% more expensive than the V-0 grade, but for low-risk scenarios, the V-0 grade is sufficient to meet safety requirements. The correct approach is to select the flame retardant grade based on the application's fire risk assessment.

Misunderstanding 3: "FR4 Insulation Performance Does Not Degrade Over Time"

Although FR4 has good environmental resistance, its insulation performance will gradually degrade under long-term harsh conditions (e.g., high temperature + high humidity). For example, FR4 used in outdoor communication cabinets for 8 years may have a volume resistivity reduced from 10¹⁴ Ω·cm to 10¹² Ω·cm (still meeting the minimum insulation requirement of 10¹⁰ Ω·cm for electronic components, but requiring regular inspection). It is not advisable to use FR4 beyond its design service life (usually 5-10 years) to avoid insulation failure.

Misunderstanding 4: "All FR4 Can Be Used for Lead-Free Soldering"

Lead-free soldering requires the material to withstand 260℃ high temperature for 10-30 seconds. Only medium and high Tg FR4 (Tg ≥150℃) can meet this requirement—low Tg FR4 (Tg = 130℃) will soften and deform under 260℃, leading to warping of the circuit board or detachment of components. For example, if a low Tg FR4 circuit board is used in lead-free soldering of a smartphone motherboard, the board may bend by more than 1mm after soldering, causing short circuits between adjacent circuits. Therefore, when designing components that require lead-free soldering (now the mainstream in the electronics industry), it is necessary to clearly specify the Tg grade of FR4 and avoid using low Tg products.

Misunderstanding 5: "FR4 with the Same Grade Has Consistent Performance"

Even for FR4 of the same grade (e.g., UL94 V-0, Tg 150℃), there may be performance differences between different batches or manufacturers. This is because the quality of raw materials (e.g., purity of glass fiber cloth, type of epoxy resin) and process control accuracy (e.g., impregnation uniformity, hot pressing temperature stability) vary. For example, two batches of V-0 grade FR4 may have volume resistivity of 10¹⁴ Ω·cm and 10¹³ Ω·cm respectively—the latter is at the lower limit of the standard and may not be suitable for high-precision insulation scenarios. Therefore, before mass production, it is necessary to sample and test the FR4 of each batch, verifying key indicators such as flame retardancy, insulation, and temperature resistance, rather than relying solely on the grade label.