Blog  /  High-Frequency PCB: A High-Speed Circuit for Signal Transmission

High-Frequency PCB: A High-Speed Circuit for Signal Transmission

Are you a technician dealing with signal transmission or wireless networking equipment? One of the critical components in these devices is a high-frequency PCB.

These circuits are also vital in electronics like cell phones because they are responsible for data transmission.

We have looked at these PCBs in detail below, including the high-frequency designs, so read on to learn more.

 

What is a High-Frequency PCB?

 

High-frequency printed circuit boards are electronic devices used to transmit electromagnetic waves with a frequency range of between 500MHz to 2GHz.

 

A high-frequency PCB

A high-frequency PCB

 

Since the circuit board has fast signal flow rates and high signal sensitivity, manufacturers build them using high-frequency laminate materials. These end up reducing the dissipation factor and stabilizing the dielectric constant.

 

The Features of High-Frequency PCBs

 

  • Low and stable Dk (Dielectric Constant)
  • Small Df (Dissipation Factor)
  • High heat resistance
  • Impact endurance
  • Chemical resistance
  • Peel off resistance
  • Low water absorptivity
  • Similar thermal expansivity to copper foil
  • Low dimensional stability
  • Adequate board spacing

 

Advantages of High-Frequency PCBs

 

  • Reduced moisture rate
  • Excellent thermal management
  • Impedance control
  • Dimensional/mechanical stability
  • Excellent signal performance with reduced signal loss

 

Applications of High-Frequency PCBs

 

  • Automotive, Airborne, and Ground-Based Radar Systems

 

Radar Systems

Radar Systems

 

  • Global Positioning Satellite Antennas
  • Cellular Telecommunications Systems
  • Direct Broadcast Satellites
  • Missile Guidance Systems
  • RFID Tags (Radio-Frequency Identification)

 

A sticker with an RFID chip

A sticker with an RFID chip

 

  • Millimeter-Wave Applications
  • Space Satellite Transceivers
  • E-band Point-to-Point Microwave Links
  • Personal or Healthcare Monitors
  • Medical Scanners (MRI, Ultrasound, CT, and more)
  • Power Indicators and Control Devices
  • Industrial and measuring equipment
  • Scientific instruments (photometers, microscopes, and control systems)

 

Laboratory microscope

Laboratory microscope

 

Materials Used For High-Frequency PCBs

 

High-frequency boards require unique PCB materials to produce the high-speed signal output. Some of these unique materials include:

  • FR4: The least expensive laminate material and is easy to fabricate. However, it has relatively poor electrical performance, especially when the signal speed goes past 1.6GHz.
  • Rogers 4350B HF: Like FR4, this material has a low fabrication cost, a competitive price, and offers excellent dimensional stability.
  • ISOLA IS620 E-fiberglass: Although challenging to fabricate, this material provides excellent thermal properties and electrical performance.
  • Taconic RF-35 Ceramic: This is a low-cost material consisting of ceramic-filled PTFE with woven glass. It is moderately easy to fabricate the material, but it has excellent peel strength, good electrical performance, and low dissipation.
  • Taconic TLX: Consisting of PTFE fiberglass, TLX is a dimensionally stable material with excellent mechanical, thermal, and electrical properties. However, it is challenging to fabricate.
  • Rogers RO3001: A bonding film with a low loss tangent and dielectric constant. It is also resistant to chemicals and high temperatures.
  • Rogers RO3003: The RO3003 consists of PTFE glass materials that provide low Dk loss and economical pricing.
  • ARLON 85N: A pure polyamide resin with high thermal resistance

Different manufacturers offer varying material combinations for high-frequency applications, but generally, they are either:

  • FR-4
  • Ceramic-filled PTFE
  • PTFE with woven glass
  • Ceramic-filled hydrocarbon
  • PTFE with micro-glass fiber
  • Ceramic-filled hydrocarbon with woven glass
  • Ceramic-filled PTFE with woven glass

 

Issues With Manufacturing HF Boards

 

Printed circuit board manufacturing

Printed circuit board manufacturing

 

Weak Binding Force

 

Since there is a dense placement of buried vias covered in resin in the PCB, there is usually a low binding force between the reinforcing prepreg sheet and the resin.

As a result, some surfaces may experience delamination, especially after soldering at high temperatures.

Manufacturers usually use resins with a comparable Tg and CTE to the substrate material to prevent delamination.

The goal is to make the two layers contract and expand at a similar rate to ensure they remain bound together even as the temperature fluctuates.

 

Drilling

 

High-frequency multilayer boards need multiple through holes for efficient heat dissipation, but this is not easy during the PCB fabrication process.

Drilling generates heat, and the melted debris from this process can solidify on the hole walls, resulting in dismal heat dissipation performance, which affects the high-frequency circuit.

The solution is to use a resin cover instead of an aluminum one, which absorbs heat better when drilling. It also helps to increase the suction and vacuuming pressure to improve the hole quality.

 

PCB drilling

PCB drilling

 

Back-Drilling

 

While the through holes help with heat dissipation, they can affect the integrity of the high-frequency signals. The extra stub acts as a reflecting path, which increases the insertion loss.

The only way to work around this problem is by drilling a wider hole on the reverse side to get rid of the extra stub.

However, the issue comes from the burrs that remain after drilling. Manufacturers can avoid them by drilling the holes before etching.

 

Surface Finish Selection for High-Frequency PCBs

 

Surface finishing gives the PCB extra strength and appeal. The options to use include:

 

HASL

 

HASL (Hot Air Solder Leveling) involves dipping the PCB in a melting solder bath, then placing it on a path with hot wind. The airflow smoothens and brightens the coat while also making it more uniform.

It is the most commonly used surface finish method due to its low cost and high shelf life.

However, the method increases the chances of solder bridging in fine pitch PCBs, while the lead component makes it a health risk. There is also the issue of thermal shock.

 

ENIG

 

Like HASL, ENG is an abbreviation, standing for Electroless Nickel and Immersion Gold, and it involves depositing gold and nickel layers on the copper PCB.

The chemical electroplating method creates a coat with a long shelf life and is perfect for plating through holes. Also, it complies with RoHS regulations, so it is safe to use.

However, it is expensive and can increase signal losses if not applied correctly.

 

A multilayer PCB with a copper-gold ISA

A multilayer PCB with a copper-gold ISA

Source: Wikimedia Commons.

 

ENEPIG

 

Electroless Nickel Electroless Palladium and Immersion Gold is similar to ENIG but eliminates the creation of a metal compound (black pads) between the gold and nickel layers. It does so by introducing a stable palladium layer.

The finish also results in better soldering, makes the surface smoother, and enhances oxidation & heat resistance.

 

Immersion Tin (IT)

 

Immersion Tin is one of the more traditional methods and involves depositing tin on the circuit board base via chemical displacement. The deposited layer protects the copper underneath from oxidizing and does not have any lead, so it is safe.

However, the process is prone to creating tin whiskers. While IT is ideal for press-fit insertion PCBs, it is unsuitable for multiple assembly processes.

 

An Immersion Tin PCB

An Immersion Tin PCB

 

OSP

 

OSP (Organic Soldering Preservative) uses a water-based organic compound to prevent copper oxidation.

The process applies a thin, flat layer cost-effectively, but the finish has a short shelf life, and it is impossible to measure its thickness. OSP is also not ideal for board layouts with plated through holes.

 

High-Frequency PCB Design Guidelines

 

PCB design

PCB design

 

As a circuit designer, you need to follow these guidelines:

 

Plan Your Design

 

Before beginning the process, lay out your ideas on a checklist to avoid forgetting vital aspects that might cause drawbacks later.

 

Determine the PCB Signal Frequency

 

Note down the power and voltage requirements for the integrated circuits, and determine if you will be dividing any power planes.

Try to accommodate all the different signals, trace lengths, and controlled impedance while minimizing the noise of the HF signals.

 

Draw Up Board Stack Up Plan For Production

 

After planning the board design, note down the requirements of the stack-up layer while consulting your PCB manufacturer to determine the specific materials.

 

Plan the Floor

 

Next, plan the floor by dividing the PCB into logical sections and decide whether to place the sub-circuits into a larger layout or make them separate.

This step is vital if you have analog and digital signals that should remain isolated to reduce interference.

 

Determine the Power and Ground Planes

 

After defining the board layout, examine it to understand the ground plane and check whether it is complete.

If not, you must divide the ground plane by including a resistor along the signal trace. The goal is to have a bridge to enhance the return path.

 

Prototype printed circuit design isolated

Prototype printed circuit design isolated

 

Minimize the Size of Land Patterns

 

One characteristic of HF boards is small pads, so the next step is to minimize the size of the land patterns.

While other PCBs have a capacity of 30% of the component pins, HF PCBs usually have 0 - 5%, so reduce its size to make it more useful. A smaller board is also mechanically more robust and minimizes parasitic capacitance.

 

Route the Frequency Signals

 

High-frequency signals emit high radiation, so routing them increases the shielding benefits of your PCB, which helps to reduce interference.

 

Design an Efficient Current Return Path

 

Each signal in a high-frequency board needs a route, which starts at the source and terminates at the sink. In between the two should be a smooth path with minimal obstruction.

 

Use 3W Rule to Reduce Trace Coupling.

 

Line coupling can severely affect signal integrity, but the 3W rule can help by increasing the distance between the lines. It states that the distance between the traces should be 3X the width of one line.

 

Apply 20H Rule to Reduce Plane Coupling

 

Coupling between the ground and power planes can damage your HF circuit board.

The 20H rule helps solve this problem because it suggests you keep the dielectric thickness between the ground and adjacent power 20X thicker than the power plane. 

 

Fabrication Process for High-Frequency PCBs

 

After designing, the next stage is PCB fabrication, which involves these steps.

 

Make a PCB Design

 

Begin by laying out the PCB blueprint on your preferred design software. You can use Extended Gerber to encode the blueprint, then send the file to the fabricator for manufacturing.

 

A Gerber project

A Gerber project

Source: Wikimedia Commons

 

Print the PCB Design

 

Also, print the PCB design, and you can use a plotter printer to produce a PCB film, which is a negative for the blueprint. It has two inks: black shows the conductive copper lines while clear ink indicates the non-conductive sections.

 

Print Copper for the Inner Layers

 

Manufacturing begins at this stage, and after printing the PCB on the laminate, copper gets pre-bonded on the same laminate, which acts as the PCB structure. Next, engrave the copper to reveal the initial blueprint.

 

A PCB copper layer electroplating machine

A PCB copper layer electroplating machine

Source: Wikimedia Commons

 

Alignment of Layers

 

Since a high-frequency PCB has different layers, manufacturers usually use optical punches to align them by forcing pins down the holes. Another machine checks whether the layers are in order, without defects.

 

PCB Layers Lamination

 

If there are no defects, the next stage involves fusing or laminating the layers and layup steps. Prepare both the inner and outer sections, then use a metal clamp to help join them.

 

Drilling

 

Use a computer-guided drill with the guidance of the Extended Gerber design to do the drilling. But before that, use an X-ray machine to determine the drilling spots. After drilling, file off the excess copper to leave the surface smooth.

 

A homemade PCB drilling machine

A homemade PCB drilling machine

 

Plating of PCB

 

Plating involves joining the layers together using chemicals. But first, you must clean the boards thoroughly before dipping them in the chemicals.

 

 

Solder Masking

 

Next, clean the panels again before applying the solder mask, then use epoxy ink with the solder film. Expose the board to UV light to expose the solder mask parts to remove.

 

PET solder tape mask on a PCB

PET solder tape mask on a PCB

Source: Flickr

 

Screening and Finishing of Silk

 

As described earlier, the finishing process involves plating the board with gold, silver, or HASL to prevent oxidation. Afterward, silkscreen the PCB to print all the essential details, such as the manufacturer name and warning labels.

 

Testing

 

This process checks the circuit isolation and continuity to ensure no shorts or disconnections exist.

 

PET solder tape mask on a PCB

An operator checks a finished PCB

 

Cutting

 

The last step is cutting the PCB either using a CNC machine or a V-a groove.

 

PCB cutting on a CNC machine

PCB cutting on a CNC machine

 

Your Expert High-Frequency PCB Manufacturer: Our Capabilities

 

Our Capabilities

 

Summary

 

As you can see, high-frequency printed circuit boards are critical components in modern electronics, and we make them using the highest standards. If you need such a circuit for your project, contact us to place your order today.

 

 

Blog  /  High Frequency PCB

High Frequency PCB

Professional engineer review; strict quality control for each process.

Advanced Testing Technology To Ensure the Quality such as AOI Test, E-Test, X-RAY, Impedance Control.

We committed to helping customers get the highest quality products and services with competitive prices (especially multilayers PCBs).

ABOUT HIGH FREQUENCY PCB?

You’re dealing with wireless networks or applications that include particular signal transmission amid objects? Consider getting a high-frequency PCB.

These PCBs come in a wide range of frequencies, starting at 500MHz and going all the way up to 2GHz. If you need high-speed design applications, they are perfect for that use case! You can also find them on microwaves or cellular devices if you’re looking for something more specific like that as well.

This type of PCB has a lot more signal sensitivity than most. That’s why it needs high-frequency laminates to help sustain the thermal heat transfer for your application.

The type of high-frequency board you choose will determine the overall performance, which can be affected to a degree by any change in the material’s dielectric constant.

The materials used for your signal boards are important because they’ll affect its impedance and how well it performs.

KEY FEATURES OF HIGH
FREQUENCY PCB

Small and stable. Besides, no delay in signal transmission.

Ideal for signal transmission. And reduce signal wastage effectively.

No copper foil separation with temperature changes.

HF boards with low water absorptivity.

Impressive properties like impact endurance, heat resistance, peel-off resistance, and chemical resistance. Plus, High peel-off resistance improves the PCB's signal quality.

Adequate spacing for boards. And It also has smaller diameter vias and invariably low conductance.

THE REQUIRED MATERIALS FOR HIGH FREQUENCY CIRCUIT BOARD

A higher frequency metal’s circuit boards are more demanding on the materials, and so one of its best features is a better permittivity.

We also have other needs similar to construction with reduced tolerance in DK and insulation thickness. It also includes a reduced attenuation for competent signal transmission.

We know how to pick out the perfect padding for all of our projects and use FR4, a material that is strong enough for most requirements. We also make sure to control high-frequency materials with enhanced dielectric properties.

And so it might be worth considering this new development in technology. This material is just what you need for your next project because, as I mentioned earlier, it has a low DK and loss factor, which will save on energy costs while also being durable enough to withstand high temperatures without melting or cracking!

Some of the materials we use are Taconic TLX, Rogers, ISOLA IS620 E-fiber glass, etc.

Here’s a table that explains each of the material’s properties:

Materials for HF circuit boardsTg (℃)CTE-z (PPM/℃)Peel Strength(N/mm)Td Value (℃)DK Loss TangentThermal Conductivity (W/m*K)Surface Resistivity(M)Electric Strength (KV/mm)Ԑr (@10GHz
ARLON 85N250551.23870.01000.201.6 x 10^9734.2
Rogers 4350B280320.93900.00370.695.7 x 10^9313.5
Rogers RO3010161.65000.00220.951 x 10^510
ISOLA IS620220541.20.00802.8 x 10^64.5
Rogers RO3006241.25000.00200.791 x 10^56.2
Rogers RO3003251.25000.00130.501 x 10^53.0
Rogers RO30011602.10.00300.221 x 10^9982.3
Taconic TLC702.10.241 x 10^73.2
Taconic TLX1352.10.00190.191 x 10^72.5

ourPCB- YOUR HIGH-FREQUENCY PCB MANUFACTURER

OurPCB has a wealth of experience in the field of PCB production. So, you can trust that you’ll get remarkable performing high-frequency PCB fabrication services. And our board usually ranges from 500MHz to 2GHz.

Here’s a table to give you an idea:

 

HF MaterialsDk
RO30033.00±[email protected] GHz
RO4350B3.48±[email protected] GHz
RT58802.20±[email protected] GHz
RO4003C3.38±@10 GHz
RO301010.2±[email protected] GHz
Properties
Capacity
Thickness of board:
0.4 – 5.0 mm
PP:
Domestic- (6700), Rogers 4450F, etc.
Silkscreen sides:
It depends on the file.
Number of layers:
2 – 32 layers
Alternative methods:
Countersink holes, Gold fingers, Peelable solder, mask Carbon oil
Silkscreen color:
Black, yellow, white
Surface finish:
Immersion tin – RoHS, ENIG – RoHS, Organic solderability preservatives – RoHS, Immersion silver – RoHS
Build time:
It depends on the project (2 days to 5 weeks)
Minimum tracing:
3mil/3mil
Material:
RO3010, RO4350B, RT5880, RO4003C, RO3003
Order quantity:
1 – 10000+pcs
Solder mask color:
Blue, red, yellow, green, white
Quality grade:
Standard IPC 2
Board size:
0.4-5.0 mm
Min drill hole diameter:
6mil
Finished copper weight:
0.5 – 2.0 0z
Min annular ring:
4mil
Impedance tolerance:
±10%

HIGH FREQUENCY PCB CASE STUDY

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