How to Select Isola PCB Materials by Operating Frequency: A Selection Guide from 1GHz to 77GHz

Why Operating Frequency Determines Material Selection

In PCB design, signal frequency is the primary factor determining substrate selection. As frequency increases, electromagnetic wave propagation loss in the dielectric grows exponentially, making the material's dissipation factor (Df) the critical bottleneck limiting system performance.

Total signal loss in PCB traces consists of three components:

• Dielectric Loss: Proportional to Df and frequency, dominant at high frequencies
• Conductor Loss: Proportional to the square root of frequency (skin effect), affected by copper foil roughness
• Radiation Loss: Becomes significant in mmWave bands

Simply put: the higher the frequency, the stricter the Df requirement. Over-specifying materials wastes cost; under-specifying degrades signal quality. Isola offers a complete product line from standard to extremely low loss, enabling designers to precisely match each frequency band's needs.

Isola Materials Recommended by Frequency Band

Tier 1: ≤1GHz — FR408HR

Applications: Industrial control, consumer electronics, low-speed digital circuits

FR408HR is Isola's entry-level low loss material, reducing loss by over 50% compared to standard FR-4 (Df≈0.020). Suitable for PCIe Gen3, USB 3.0, Gigabit Ethernet, and other mid-speed digital interfaces.

Tier 2: 1-6GHz — 370HR / I-Speed

Applications: WiFi 6/6E, Bluetooth, GPS, 4G/5G Sub-6 base stations

While 370HR has higher Df, its exceptional thermal reliability makes it suitable for scenarios where reliability outweighs signal performance (e.g., automotive electronics). I-Speed is the performance choice for this band with Df of only 0.0070, ideal for 5G Sub-6 GHz base stations and high-speed backplanes.

Tier 3: 6-30GHz — I-Tera MT40

Applications: 5G mmWave base stations, satellite communications, high-speed SerDes (112Gbps PAM4), AI server interconnects

I-Tera MT40 is Isola's flagship ultra-low loss material with Df of only 0.0031 at 10GHz, making it the gold standard for high-speed digital and mid-frequency RF applications. Its excellent Dk stability and standard FR-4 processing compatibility make it the preferred material for data center switches and AI servers.

Tier 4: 30-77GHz+ — Astra MT77

Applications: 77GHz automotive radar, 60GHz WiGig, satellite Ka-band, mmWave 5G

Astra MT77 is Isola's ultimate solution for mmWave frequencies. Its extremely low Df and excellent Dk temperature stability enable acceptable insertion loss at 77GHz. More importantly, it is PTFE-free and fully compatible with standard PCB processing.

Full Series Parameter Comparison

Material Selection Decision Tree

Follow this process to quickly determine the most suitable Isola material:

• Step 1: Determine Maximum Operating Frequency

  • For digital signals, take 5x the Nyquist frequency (e.g., 28Gbps NRZ → 70GHz)
  • For RF signals, use the carrier frequency

• Step 2: Determine Loss Budget

  • Calculate maximum allowable insertion loss (dB/inch)
  • Subtract conductor loss to get dielectric loss budget

• Step 3: Determine Reliability Requirements

  • Automotive/aerospace grade → prioritize Tg, Td, CAF
  • Consumer/commercial grade → can relax somewhat

• Step 4: Determine Cost Constraints

  • Material cost: Astra MT77 > I-Tera MT40 > I-Speed > FR408HR
  • Processing cost: All Isola materials are compatible with standard processes, minimal difference

• Step 5: Consider Hybrid Stackups

  • Use premium materials for RF layers, economical materials for digital layers
  • Isola's full product line has well-matched CTE, ensuring hybrid lamination reliability

Hybrid Stackup Strategy: Optimal Balance of Performance and Cost

A major advantage of the Isola material system is that all products are based on similar resin chemistry with close CTE and processing parameters, making them ideal for hybrid stackup designs:

• RF + Digital Hybrid: Astra MT77 for antenna layers, I-Tera MT40 or I-Speed for digital layers
• High-Speed Backplane: I-Tera MT40 for signal layers, FR408HR for power/ground layers
• Automotive Radar: Astra MT77 for RF front-end, 370HR for signal processing board

Hybrid stackups can reduce overall material costs by 30-50% without sacrificing signal performance on critical layers.

Common Material Selection Mistakes

• Mistake 1: Always choosing the lowest Df material — Over-engineering increases cost; select based on actual frequency and loss budget
• Mistake 2: Only looking at Dk/Df while ignoring reliability — In automotive and industrial applications, Tg, CAF, and thermal cycling are equally critical
• Mistake 3: Using 1GHz data to evaluate high-frequency performance — Must reference measured data at the target frequency
• Mistake 4: Assuming low-loss materials are difficult to process — All Isola materials are compatible with standard FR-4 processes, no special equipment needed
• Mistake 5: Ignoring copper foil contribution to total loss — At high frequencies, conductor loss can account for 40-60% of total loss; HVLP foil is essential

Sunking PCB Isola Material Processing Capabilities

Sunking PCB has established a long-term partnership with Isola and offers PCB manufacturing services for the full range of Isola materials:

• Full inventory of FR408HR, 370HR, I-Speed, I-Tera MT40, and Astra MT77
• Extensive hybrid stackup lamination experience
• High-frequency impedance control accuracy ±5% (including 77GHz verification capability)
• Free material selection consultation and stackup design recommendations
• Signal integrity simulation support (SI/PI co-design)
• Full-process service from prototype validation to volume production