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- November 28, 2022
- PCB knowledge
- (0)
- 06 mins
What is high frequency PCB and its features and applications
Worried about getting desired output in high-speed electronic instruments? High frequency PCB can handle high-speed components with superior efficiency.
Do you have an in-depth idea of these circuit boards?
If negative, nothing to worry about. This article will let you know the ins and outs of high-frequency circuit boards. So, let’s dig deeper.
What is a high frequency PCB?
High frequency PCB is a kind of circuit board that deals with signal frequencies 500MHz to 2GHz. But it is compatible with more than 2GHz frequency in some cases.
This is a must-have component of high-speed signal transmission in radio frequency, mobile, microwave, etc.
What are the features of high frequency PCBs?
High frequency PCBs offer notable features that include:
Low loss tangent
The loss tangent or dissipation factor indicates the rate of deficiency and signal loss with respect to the frequency. High frequency circuit boards ensure a low dissipation factor (0.0019-0.25). That means this PCB offers commendable performance during its operation.
Low dielectric constant
Dielectric constant (DK) tells you the ability to store the charge of a material. Its higher value indicates the high signal delay with the low-frequency transmission which is not expected at all in high-speed and high-frequency applications.
This circuit board consists of such materials that offer DK value within 4.8-5.4 which is superb, without any doubt.
Standard dimensional stability
HF (High-Frequency) PCBs remain almost the same under high temperatures and mechanical stress. These properties indicate their standard dimensional stability.
Besides, its chemical resistance is also high, which keeps the board durable in different environments.
Improved impedance matching
This PCB ensures impedance control in signal transmission applications.
Low moisture absorption
Its moisture absorption rate is almost 0.012%, which is very low. It means you can use HF PCB in intense humid conditions.
Applications of high frequency PCB
The most notable applications of a high frequency PCB includes:
●Communication: Mobile, amplifier, radars, booster, E-Band point-to-point Microwave links, high-speed interconnects, millimeter-wave applications, etc.
●Medical industry: Diagnostic devices, monitoring equipment.
●Military industry: Firearms, Ammunitions.
●Space-satellite transceivers
Materials used for high frequency PCB
The major materials of High frequency PCBs are:
●Rogers 4350B, Rogers 3003, Rogers 3010
●FR4
●CEM
●Taconic ceramic (RF-35), Taconic TLX
●Isola Fiberglass (IS-620)
●PTFE (Poly Tetra Fluoro Ethane)
●Arlon 85N
Which transistor is most suitable for high frequency circuits
A grown Junction transistor, which is a kind of BJT (Bipolar Junction Transistor) is the most suitable for high-frequency circuits. Its other name is the Grown Diffusion Transistor.
Usually, an NPN Grown Junction transistor is more widely used than a PNP transistor. It has a specialty in dealing with high-frequency signals in high-speed applications.
How to design a high frequency PCB?
As high frequency PCB deals with a signal frequency of more than 1 Hz, you have to face some challenges while designing this circuit board Along with maintaining IPC standards to achieve reliability and improved functionality, you must consider the following factors in this case:
• Signal degradation
• Parasitic capacitance
• EMI radiation
• Impedance matching
• EMI absorption
• Harmonic distortion
• Surface tracking
• Common mode noise, etc.
That’s why you have to follow some reliable guidelines in terms of material selection, component placement, grounding, routing, shielding, and so on.
Feeling puzzled?
Don’t be so. Here, we are going to share a flawless guideline with you so that you can optimize your high frequency PCB design to deal with high frequencies. Let’s have a look.
PCB materials selection
This is a crucial part of PCB design. You need to ensure the use of:
●Solder mask to decrease the loss tangent
●Materials with DK value compatible with high frequency
●Copper materials with a low profile
Component placement
In this section, it is necessary to keep the components responsible for high radiation like the antenna, alienated.
Besides, place the components in a group concerning their signal type.
Most noteworthy, don’t forget to maintain the same distance between all differential traces.
Routing
Make sure that:
●Trace length becomes minimum
●Space between traces remains maximum
●Different signal types get routed on separate layers
You can apply 3W rules (Trace distance = 3*Trace Width) to decrease the trace coupling.
Besides, 20H rule (Distance between the Ground and adjacent power = 20*Power Plane) is useful to reduce the plane coupling in high-frequency circuit design.
Grounding
●Different signal types should be placed on different grounds
●Don’t use splitting ground planes with signal layers
Shielding
You must use EMI shields for high-radiation components.
Stackup
In this case, a symmetric PCB stack up is preferable on any day.
Moreover, you can apply high-pass and low-pass filters to avoid excessive noise and EMI.
Last but not the least, maintain the standards of clearance and creepage.
After managing these issues, it is required to set up and manage the constraints through PCB design software. Cadence, Altium Designer, etc are worthwhile software to handle the electrical, thermal, and mechanical constraints properly.
Then, the last thing is the design verification so that you can avoid minute defects.
Design verification
Most of the reputed design software offer design verification. You can be sure that the design is compatible with DFM capabilities, without any violation of the rules.
Besides, you can check the thermal state, signal flow, packet data network, etc through simulation.
Fabrication process for high frequency PCBs
The entire fabrication process consists of several steps that are listed below for your convenience.
●First, you need to make a blueprint of your PCB design by using software.
●Send the blueprint to the manufacturer for fabrication.
●Next, print the PCB design through a plotter printer that acts as a negative of the design.
●Print the copper for the inner layers.
●The next thing is layer alignment which is done by using optical punches. This punch actually applies force to the pins so that they get fit into the holes. You have to check whether the layers are in order or not.
●Then, lamination comes to the place that is basically binding the inner and outer layers through metal clamps.
●Now, the fabricator conducts an Automated X-Ray Inspection to determine suitable spots for drilling and starts drilling both manually or using computers.
●Then, erase the unnecessary copper so that the PCB surface becomes plain.
●Clean the entire board properly.
●Then place the board in a chemical that is named the plating of circuit boards.
●Again, clean the PCB.
●Now, use the solder mask and film with Epoxy inks on the panel.
●Then, apply a suitable surface finish like HASL, ENIG, etc to protect the board from oxidation and corrosion.
●Silkscreen the circuit board. It helps print all necessary texts. Such as warnings, manufacturer’s name, etc.
●Check the functionality of the PCB through a manual or automated test. Numerous automated tests like AXI, AOI, Flying Probe Test, etc are reliable in this case.
●At the end of testing, the fabricator cuts the circuit board via a V-groove or a CNC machine.
You can check this video to get a better understanding.
Considerations when choosing high frequency PCB substrate
It will be beneficial for you to consider some subjects when you intend to choose a high-class high frequency PCB substrate:
●Manufacturer
●Frequency Range
●PCB materials selection
●Impedance matching
●Coefficient of Thermal Expansion
●Ground Plane Design
●Component sourcing
●DK value
●Dissipation Factor
●Moisture Absorption Rate
●PCB via placement to get an idea about the bending force
High frequency PCB is a kind of circuit board that deals with signal frequencies 500MHz to 2GHz. But it is compatible with more than 2GHz frequency in some cases.
A grown Junction transistor, which is a kind of BJT (Bipolar Junction Transistor) is the most suitable for high-frequency circuits. Its other name is the Grown Diffusion Transistor.
- Low loss tangent
- Low dielectric constant
- Standard dimensional stability
- Improved impedance matching
- Low moisture absorption
Final thoughts
These are the main points about high frequency PCB. IBE is a dependable PCB manufacturer in China that also offers reliable ODM and OEM services. It delivers PCBA manufacturing services for around 17 years.
So, contact us to experience the excellence in high-frequency PCB assembly.
