Description
High Frequency PCB is a kind of printed circuit board specially designed for processing high frequency signals, its operating frequency is usually above 1GHz, mainly used for high frequency (frequency greater than 300MHz or wavelength less than 1 meter) and microwave (frequency greater than 3GHz or wavelength less than 0.1 meters) application scenarios.
High Frequency PCB Material Selection Guide
1. PTFE (Polytetrafluoroethylene) Substrates
The material of choice for high-frequency applications, PTFE offers excellent performance advantages due to its unique molecular structure:
Extremely low dielectric constant (Dk) and loss factor (Df) to ensure signal transmission integrity.
Excellent chemical inertness and weatherability for harsh operating environments
Wide operating temperature range (-200°C to +260°C)
Excellent mechanical toughness for multilayer board processing
Typical applications: millimeter wave radar, satellite communications, aerospace electronics.
2. Limitations of FR-4 Materials
Although FR-4 dominates common PCBs due to its cost advantages, there are significant shortcomings in its high-frequency performance:
Dielectric constant fluctuates significantly with increasing frequency (4.3-4.8@1GHz)
High loss factor (0.02-0.025), resulting in severe signal attenuation.
Poor temperature stability, affecting the reliability of high-frequency circuits
Scenario: limited to low-frequency circuits below 1GHz.
3. High Performance High Frequency Laminates
Composite material system optimized for high frequency:
Matrix resin: modified polyimide (PI), liquid crystal polymer (LCP)
Reinforcement system: Ultra-fine glass fiber/ceramic powder filling
Typical parameters: Dk=2.5-3.5, Df<0.005@10GHz
Advantage: Excellent Z-axis CTE consistency, suitable for HDI design
Application areas: 5G base station AAU, automotive 77GHz radar, high-speed backplanes
4. Special advantages of ceramic substrates
Core features of Aluminum Oxide (Al₂O₃) and Aluminum Nitride (AlN) substrates:
Ultra-high thermal conductivity (up to 170 W/mK for AlN)
Near-zero coefficient of thermal expansion (6-8 ppm/°C)
Laser Direct Writing Process Compatibility
Co-firing process compatibility with gold/silver conductors
Typical Configurations: Thin Film Ceramic Circuits (TFCC), Low Temperature Co-fired Ceramics (LTCC)
Selection Recommendations
A systematic approach to evaluation is recommended:
1. Electrical performance matrix: establish Dk/Df versus frequency curve
2. Reliability verification: Perform a 1000 thermal cycle (-55°C~+125°C) test
3. Processability evaluation: Examine drill roughness, plasma treatment effect
4. Cost modeling: Calculate full life cycle cost (including RF test loss)
Core features of high-frequency PCBs
1. Ultra-low Loss and Efficient Transmission
High-frequency PCBs utilize substrates with low dielectric constants (Dk<3.0) and ultra-low loss factors (Df<0.005), which significantly reduce signal transmission losses and improve energy conversion efficiency. This feature makes it excellent for applications such as induction heating and RF energy transfer, and is especially suitable for industrial scenarios where energy efficiency is critical.
2. Fast Signal Transmission
By optimizing the substrate’s dielectric properties (e.g., PTFE or modified ceramic filler materials), the propagation delay of high-frequency PCBs can be reduced to less than 5.6ns/m@10GHz. This meets the needs of applications with high signal integrity requirements, such as 5G communications, high-speed SerDes (56Gbps+), and millimeter-wave radar.
3. Precise Energy Control
The electromagnetic field distribution of high-frequency PCB is highly controllable and supports:
Three-dimensional gradient heating (e.g., selective heating at different depths in metal heat treatment)
Localized focused energy delivery (targeted therapy for medical RF ablation devices)
Dynamic impedance matching (VSWR < 1.2 by optimizing the transmission line structure).
4. Adaptability to harsh environments
Humidity resistance: water absorption <0.02% (much lower than FR-4’s 0.1%), suitable for high humidity environments
Chemical inertness: resistant to acid and alkali solvents and oxidizing environments (IPC-4103 compliant)
Temperature stability: dielectric constant temperature drift coefficient <50ppm/°C (-40°C~150°C)
High-frequency PCB manufacturing process analysis
High-frequency PCB manufacturing is a complex process that integrates material science and precision machining technology, the core of which is to achieve excellent signal integrity and stable high-frequency performance. The following are the technical points of the key manufacturing processes:
1. Special base material selection
Preferred international, well-known high-frequency material system:
PTFE substrate: Rogers RT/duroid series (Dk=2.2- 10.2)
Ceramic filled composites: Taconic RF-35 (Df<0.0015@10GHz)
Modified epoxy system: SangYi S7136H (for 77GHz vehicle radar)
Selection should consider the Dk/Df temperature coefficient, Z-axis CTE matching,g and processing window.
2. Precision Molding Processing
Laser microfabrication:
UV laser drilling (hole diameter ≤75μm)
Picosecond laser cutting (kerf roughness Ra<5μm)
High precision lamination control:
Vacuum hot pressing process (pressure 30-50kg/cm²)
Rising temperature slope ≤3℃/min (to prevent PTFE phase change)
Multi-layer interconnection process
Mixed pressing technology:
PTFE and FR-4 mixed lamination needs to be used:
Specialized bonding sheets (e.g. RO4450B)
Stepped ramp-up profile (peak temperature 280±5°C)
Back drilling technology:
Use of depth-controlled drilling rigs (accuracy ±25μm) eliminates stub effect
4. Line graphing
Modified Semi-Additive Process (mSAP):
Chemical copper plating thickness control (0.5-1μm)
Differential line width tolerance ±8% (@100Ω impedance)
Plasma treatment:
Activation of PTFE surface using CF4/O2 gas mixture
5. Functional surface treatment
| Surface Finish |
Technical Specifications |
Key Applications |
Performance Advantages |
| ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold) |
– Ni: 3.0±0.5μm
– Pd: 0.1-0.2μm
– Au: 0.05-0.1μm |
– RF connectors
– High-frequency interconnects
– BGA packaging |
– Excellent corrosion resistance
– Superior solderability
– Long shelf life (12+ months) |
| Chemical Silver Immersion |
Ag: 0.2-0.5μm
Surface roughness: ≤0.3μm Ra |
– Millimeter-wave antennas (24- 77GHz)
– High-speed digital circuits |
– Low insertion loss (<0.1dB@10GHz)
– Cost-effective solution
– Excellent high-frequency performance |
| Electroplated Hard Gold |
– Au: 1.0±0.2μm
– Hardness: 180- 220HK
– Underlayer Ni: 2-5μm |
– RF switches
– Test points
– Wear-contact components |
– Superior wear resistance
– >10,000 mating cycles
– Stable contact resistance |
6. Full Process Quality Verification
Online Inspection:
Time Domain Reflectometer (TDR) impedance test (±5%)
Infrared Thermal Camera (ITC) to detect lamination defects
Reliability Verification:
1000 thermal cycles (-55℃~125℃)
85℃/85%RH high temperature and high humidity test
Process control points:
1. Ambient temperature and humidity control (23±2℃, 45±5%RH)
2. Dielectric layer thickness tolerance ≤ ± 8%
3. copper foil surface roughness Rz<2μm (HVLP copper)
4. Plasma de-drilling treatment (required for PTFE materials)
Topfast — Your High-End PCB Manufacturing Partner
Company Profile
Topfast was founded in 2008, as a professional PCB manufacturer with 17 years of industry accumulation, we have always been committed to providing global customers with high-end circuit board total solutions. Through continuous technological innovation and strict quality control, Topfast has become a trusted PCB service expert in the electronics industry.
Core Competencies
Full range of product lines:
✓ High-frequency/high-speed PCBs (up to 77GHz applications)
✓ High Density Interconnect (HDI) boards (minimum line width/space 2/2 mil)
✓ High Power Thick Copper Boards (up to 20oz copper thickness)
✓ High multilayer backplanes (up to 40 layers)
✓ Semiconductor test probe boards
✓ Rigid-flex boards
Certification System:
▶ UL Safety Certification
▶ IPC Class 2/3 Standard
▶ ISO9001:2015 Quality Management System
▶ RoHS/REACH Environmental Compliance
Technical Advantages
1. High Frequency Board Specialized Capabilities:
Adopting Rogers/Taconic and other top high-frequency materials
Impedance control precision ±5% (@50GHz)
Specialized PTFE processing technology
2. Intelligent manufacturing system:
Equipped with LDI laser direct imaging equipment
Adopt a fully automatic AOI inspection system
Introduction of high-precision flying probe tester
3. Value-added services:
Pre-DFM design optimization
Signal integrity analysis
Thermal management program design
Quality Commitment
We establish a perfect quality assurance system:
100% incoming inspection of raw materials
CPK≥1.33 for key processes
100% electrical performance test
FA full inspection for shipment
Service Concept
Topfast adheres to the business philosophy of “Technology Leadership, Quality First” through:
✔ Professional FAE team for full technical support
✔ Flexible and fast response mechanism
✔ Customized solutions
To create maximum value for customers, help customers achieve product success.
Contact Us
Welcome to visit our company’s official website or call our customer service hotline. Our technical team is always ready to provide you with professional advice and project support. Let’s work together to create a better future for electronic technology!