High Frequency (HF) PCBs
The definition of High Frequency PCB may vary by different industries, but HF PCB is evolved from antenna. Different from traditional wire antenna or loop coil antenna, two or more antennas are embedded into a circuit board as etched copper structures, we can call this type of circuit board as high frequency PCB, which performs the functionality of an antenna for generating, evaluating, emitting and receiving radio frequency signals of over 1 GHz.
High Frequency PCBs can transmit electromagnetic waves in the frequency of GHz with minimal loses, which also contain Radio Frequency (RF) PCBs and Microwave (MW) PCBs. They can be widely used in wireless products from handed devices for medical and industrial applications to advanced communication systems for base stations, radars and global positioning etc. And for some special fields like military and aerospace, High Frequency PCBs are also crucial components for these advanced and complicated applications.
Characteristics of High Frequency PCBs
High Frequency PCBs take place of common FR4 PCBs to be used on many high-tech applications are based on their special advantages:
- Lower and More Stable Dielectric Constant (DK) : High Frequency PCBs have lower and more stable Dielectric Constant, which improves frequency transmission and reduces signal delay.
- Lower Dissipation Factor (DF) : High Frequency PCBs have a lower dissipation factor than common PCBs do, which helps to ensure the signal transmission rate and minimize signal loss.
- Lower Moisture Absorption: High Frequency PCBs have lower rate of humidity absorption, so they can withstand a humid environment without affecting frequency transmission quality.
- Smaller Coefficient of Thermal Expansion (CTE): The smaller CTE of High Frequency PCBs ensures better thermal resistance and reduce the impact on RF performance caused by high temperature.
- Stronger Chemical Resistance Ability: Due to special materials used, High Frequency PCBs have excellent chemical resistance and they are less likely to get corroded.
Materials Used for High Frequency PCBs
The great characteristics enable High Frequency PCBs can be utilized for many high-tech and high-value applications. Actually the secret behind the excellent performance and expensive price of HF PCBs is the base materials used.
For normal applications, standard FR4 materials (FR4 is a composite material composed of woven fiberglass cloth with an epoxy resin binder that is flame resistant. “FR” stands for “flame retardant” and indicates that the material is compliant with the UL94V-0 standard on plastic material inflammability.) with heat resistance between TG135 to TG150 will be good enough. But for some circuit boards like High Frequency PCBs need to work under extreme circumstances, higher grade materials should be selected instead of common FR4 materials..
The ideal base materials for High Frequency PCBs are PTFE, Ceramic, Low Loss / Low DK & Higher Performance FR4, PI, Ceramic-Filled PTFE, Ceramic-Filled Hydrocarbon, Polyphenylene Oxide and E-Fiber Glass etc.
The table below shows the optional base materials for High Frequency PCBs:
|Material for HF PCBs||DK||DF||TG||TD||Z CTE||Surface Resistivity||Thermal Conductivity||Peel Strength|
|Rogers RO4003C||3.38||0.0027||>280||425||46||4.2 x 109||0.71||1.05|
|Rogers RO4350B||3.48||0.0037||>280||390||32||5.7 x 109||0.69||0.88|
|Rogers RO3003||3||0.0013||–||500||25||1 x 107||0.5||2.2|
|Rogers RO3006||6.2||0.002||–||500||24||1 x 105||0.79||1.2|
|Rogers RO3010||10||0.0022||–||500||16||1 x 105||0.95||1.6|
|Isola IS620||4.5*||0.008||220||–||55||2.8 x 106||–||1.2|
|AGC Taconic RF-35||3.5**||0.0018||315||–||64||1.5 x 108||0.24||1.8|
|AGC Taconic TLX||2.5||0.0019||–||–||135||1 x 107||0.19||2.1|
|AGC Taconic TLC||3.2||–||–||–||70||1 x 107||0.24||2.1|
|ARLON 85N||4.2*||0.01||250||387||55||1.6 x 109||0.2||1.2|
Design Considerations for High Frequency PCBs
Before and during the design of a High Frequency PCB, design engineers should take these factors into consideration:
– Determining PCB Signal Frequency
– Planning Board Stack-up
– Determining Power and Ground Planes
– Determining Routing Methods and Length
– Plan Number of Vias
– Avoiding Crosstalk
– Adding High-Frequency Decoupling Capacitors
– Isolating the Ground of High-Frequency Digital Signals and the Ground of Analog Signals
– Adopting Fly-by Topology for DDR4
– Adopting the 20H Rule to Minimize Plane Coupling
– Making Proper Signal Impedance Matching
As a professional PCB design engineer with good expertise and experience on designing High Frequency PCBs, these tips are common sense. Among them, we’d like to talk a little bit more about controlled impedance design.
Any mismatch on impedance will lead to signal reflections in the transmission channel. So it’s very important to know how to design controlled impedance transmission lines – Microstrip and Stripline.
In X-Parts, our experienced engineers will be happy to provide impedance control advice along with stack-up adjustment suggestions as per your requirements. We can also provide Testing Controlled Impedance Coupons and testing reports for your verification.
Please feel free to require engineering support from our team during your High Frequency PCBs design and require a quote from us for your finished design.
X-Parts High Frequency PCBs Manufacturing Capabilities
|Technology Highlights||Controlled Impedance, Low Loss Materials|
|Materials||PTFE, Ceramic, Low Loss / Low DK & Higher Performance FR4, PI, Ceramic-Filled PTFE, Ceramic-Filled Hydrocarbon, Polyphenylene Oxide and E-Fiber Glass|
|Board Thickness||0.2 MM – 3.2 MM|
|Dielectric Thickness||0.1 MM – 3.0 MM|
|Copper Thickness||0.5 OZ – 10 OZ|
|Minimum Track / Spacing||0.075 MM / 0.075 MM|
|Metal Core Thickness||0.4 MM – 2.0 MM Post Bonded|
|Maximum Dimensions||580 MM x 1080 MM|
|Surface Finish||ENIG, Immersion Tin, Immersion Silver, Electrolytic Gold, Gold Fingers (HASL / HASL LF Not Recommended)|
|Minimum Laser Drill||0.1 MM Standard, 0.075 MM Advanced|