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The types of RF PCBs are as follows:

● Two-Sided PCB

They have two conductive layers. This is the most simple form of RF PCB. Like other standard PCB, you will not find any single-sided PCBs.

Two-sided RF PCB

● Multilayer PCB

You will find more than two conductive layers in a multilayer RF PCB. The number of layers can be up to 20. This type of PCB provides more freedom to the designers.

Multilayer PCB

Radio Frequency PCBs can transmit communication signals efficiently because of their advanced components. RF PCB assemblies for communications and networking use high-frequency materials and are capable of providing various benefits to GHz and MHz applications. Here are some benefits that you will get from an RF PCB:

• The stable Er and low tangent provide high-frequency signals to go through the printed circuit board quickly and with less impedance.

RF PCB Layout

• You can combine the materials in the Multilayer circuit board stack-up. This reduces assembly costs and ensures the highest performance.
• The structure of RF PCB is highly stable in a high-temperature situation. This PCB can operate at 40 GHz if used in analog applications.
• You can pace the delicate pitch components onto the board without too much trouble and optimum efficiency.
• Because of the CTE materials used in this PCB, engineers can design complex layouts with multiple layers.
• You can stack these materials in this PCB more uniformly than other PCBs, increasing performance and reducing production costs.

The manufacturing process of RF PCB is more complex than an RF or Microwave PCB. Many problems can occur while receiving and transmitting radio signals. Therefore, strict rules need to be applied in the manufacturing process of RF PCBs.

RF PCB signals are noise sensitive compared to standard PCBs. Consequently, they require tighter impedance tolerance.

They are not really limitations of RF PCBs, but you have to consider those things when the manufacturing process.

As modern devices and applications largely depend on radio frequencies, the use of RF PCBs and Microwave PCBs are plentiful. We have listed some technologies that use RF PCBs at their core.

Wireless Technologies

TV remote, AC remote, and many other wireless applications depend on radio frequency to communicate between devices. Walkie-talkies are another excellent example of applications of RF PCBs.

Wireless Communication

In the Police and the defense department, radiofrequency is the primary source of sending and receiving communication signals using radiofrequency. Therefore, RF PCBs are widely used to develop various communicative devices in those departments.

Smart Phones

Most probably, you are reading this article using your smartphones. This is the age of smartphones, and they have overtaken many other technologies over the last decade.

Smart Phones

Smartphones are dependent on multiple wireless applications. You can share information between two mobile phones or even connect to a PC or Laptop using hotspots. RF PCBs are required for such applications that depend on radio frequency in your mobile phone.

Sensors

These days you will find sensors in various applications. From automated doors, gates to the digital indoor system, sensors are necessary to function those technologies properly.

Sensors

Those sensors you see in your everyday life are developed from RF PCBs.

Robotics and Security

Military-grade security and robotics both technology depend on RF PCB.

Robotics

Those technologies are based on radio communications, and without RF and Microwave circuit boards, you can not achieve such equipment or applications.

When you are manufacturing RF PCBs, you have to be cautious and need to make several considerations. We have told you earlier that the RF PCB manufacturing process is more complicated than standard PCB. You also have to follow those standards when selecting materials for RF PCB manufacturing.

The materials you will use must include dissipation factor, dielectric constant, and coefficient of thermal expansion.

Considering the thermal conductivity and temperature coefficient of the dielectric constant would also be helpful.

High-frequency materials such as PTFE or polytetrafluoroethylene are ideal for RF PCBs for getting desirable dielectric properties.

The most reliable RF materials are the combination of PTEF, hydrocarbons, and ceramics. Sometimes different types of glasses are also applied on RF printed circuit boards. In the best quality RF PCBs, you would find a combination of PTFE and micro-glass fiber.

Though this has high CTE it comes with outstanding electrical properties. You can also achieve similar results from the combination of woven glass and PTFE.

However, you can minimize cost at the same time retaining the quality by utilizing ceramic-filled PTFE. Ceramic filled with hydrocarbons makes the manufacturing process more straightforward. However, the reliability of the signal will be less in this case.

Apart from that, the PTFE ceramics come with less moisture absorption rate. After incorporating the woven glass, the moisture level increases.

After adding hydrocarbons to the PTFE ceramic, the moisture absorption level will increase. That is the reason why this is an excellent choice to balance between humid surrounding resistance and the cost.

Using FR4 in your RF PCB manufacturing has several controversies. However, FR4 is the least expensive material to manufacture RF PCBs. Some engineers think this is an unstable one.

FR4 for RF PCB

There is a running debate whether FR4 can be used to manufacture RF PCBs that will be used in low-frequency and less demanding applications.

FR4 is the worst loss tangent (tan δ) material and unsuitable for both broadband and high-power applications. If your budget is highly compact and the planning device has low frequency and low power, you can consider FR4. Otherwise, it would be a poor material selection.

Ceramic-filled PTFE and FEP are the most common materials that you would find in RF PCB because of their low lamination temperature.

One last thing, you should also consider the re-melt temperature if the board you are developing has the chance to work in tremendous thermal conditions.

The RF PCB is also manufactured from copper like other printed circuit boards in the market. At first, copper is coated to PTFE and then sliced away, which exposes the design of your RF PCB.

The below steps are essential in the manufacturing process of RF PCB.

1^st Step: Designing The Board

This is the first step of manufacturing RF PCBs. You have to create the blueprint of the circuit board you are going to manufacture. You have to use capable computer software to design the board.

You can use a trace width calculator for achieving precise details of both external and internal layers.

2^nd Step: Printing Out The Design

After designing, you have to print out the design of your RF PCB. You can print the design using a plotter printer. The printed film comes with every detail of all the layers you are going to use on your board.

You need to use various colors for the inner and outer layers of the board. The standard rule is to represent the non-conductive with clear ink. Make sure you use black ink to indicate conductive circuits and copper traces.

You will use similar colors for the external layers, but the meaning will be the opposite.

3^rd Step: Substrate Creation

This is the step where your RF printed circuit board starts to take shape. As it is an RF PCB, you will use PTFE or polytetrafluoroethylene as the insulating material to lock up the components on the structure.

To start the formation, you have to pass the materials alongside an oven and semi-cure the content. You can pre-bond copper from any side of the layer.

Now you can etch away to unveil the design of your printed circuit board.

4^th Step: Inner Layers Printing

As you have obtained the design from the previous steps, you can now print it onto the laminate.

You have created a photo-sensitive film using photo-reactive chemicals earlier. This is the time to use that film. When you expose that to UV light, that will harden automatically. The process is called resist. You can align the actual print and the blueprint easily with that.

In the alignment process, drilling vias is an essential step. Now you can proceed with that.

5^th Step – Ultraviolet Light

You have to pass both the laminate and the resist between ultraviolet lights when the alignment is done. This process hardens the photoresist.

Moreover, the light helps to determine copper pathways. Black ink protects those areas you will remove later from hardening. Use an alkaline solution to wash the board. This process also eliminates excess photoresist.

6^th Step: Clearing Unwanted Copper

There is still some unwanted copper, and you have to remove those from the board. You will need a chemical solution to perform this procedure. As a result of this process, all the unwanted copper will be gone from your board, remaining the hardened photoresist intact.

7^th Step: Inspection

Before alignment, you have to inspect the layer you cleaned in the previous step. You must rely on the vias or holes you drilled initially for both outer and inner layers alignment.

You can drill the pins into the holes with the help of an optical punch machine. Thus you can align the layers perfectly.

You have to use another machine to perform further inspection to identify any defects in the board. You have to correct every possible mistake in this step, or you won’t be able to perfect that later and ruin the entire manufacturing process.

RF Hardware and design tips

8^th Step: Laminating

Now it’s time to join all the layers. You will need to adjust different layers with metal clamps.

You have to place the epoxy layer into the alignment basin followed by a substrate layer. The following layer is built with copper foil, and then you have got another layer of epoxy resin.

And the press plate is the final layer built with copper.

9^th Step: Layers Pressing

You have to put the layers together by using a mechanical press and punching the pins into the layers. The pins should align the board appropriately. After finishing this process, it’s time to use the laminate press.

10^th Step: Drilling

You have to use a computer-supported drilling machine to complete the drilling process of your RF PCB. The copper traces from this step will be removed.

11^th Step: Plating

When the drilling is done, it’s time to plate the board. You have to use chemical solutions to connect every layer.

Then you have to use various chemicals to coat the panel with a light layer of copper.

12^th: Imaging The Outer Layer

Apply a photoresist layer as you have applied in the 3^rd step. Then you have to use UV light to harden the photoresist. The UV light will also remove unwanted photoresist from this step.

13^th Step: Plating

This is a repetition of the 11^th step, and you have to plate the panel using a thin copper layer. This step protects the external layer from etching.

14^th Step: Etching

You can use the chemical solution when you perform etching earlier to remove additional copper. The tin guard layer protects the copper, and you can establish the connection to your PCB board at this step.

15^th Step: Solder Masking

Before applying solder masking, make sure you have cleaned all the panels perfectly. Generally, a green solder mask is used. Use ultraviolet light to remove unwanted solder masks.

16^th Step: Silkscreening

You will print every crucial information about the board in this step. From here, the PCB board will be delivered for the last cutting and curing process.

17^th Step: Surface Finishing

You should palate the RF Printed circuit board with a solderable finish.

18^th Step: Testing

This is a vital test before using your RF PCB for application. An electrician is an ideal person to test your RF PCB. That person will check the final product following the blueprint of your design.

Learn the design guideline of RF PCB

You can use two methods to mount components on RF PCBs. These are:

• Surface mounting technology (SMT)
• Through Hole Mounting. (THM)

In recent times through-hole technology is widely used. Connecting all the components to tracks in the inner layer of RF printed circuit boards is easy with this process.

PCB components

In this process, the components are easier to replace. However, you will need ample space to mount components using this technology, and placing the components manually is impossible.

With surface mounting technology, you don’t have to drill holes on the board for electrical connections. The connection between the component’s lead and the tracks is direct. Pick, and Place machines are used to achieve this connection.

Using the SMT method makes RF PCBs denser, and you can place components on any side of the board.

• The first distinctive difference between RF PCBs and standard PCBs is that RF printed circuit boards can operate more than 1000MHz, and standard PCBs can not operate under such conditions.
• The voltage and current requirements of the RF circuit boards are significantly different from standard PCBs.
• There is no single-sided RF PCB. This type of PCB has a minimum of 2 and a maximum of 20 layers.
• radio frequency PCBs are impedance and noise sensitive. Moreover, they are more at risk when exposed to electromagnetism if we compare them to standard PCBs.
• The manufacturing process of RFPCB is far more complicated than standard PCB.

These PCBs have recommended thickness. You have to limit the thickness within that range.

The most effective range of thickness for RF PCB is between .1 mm to 3.0 mm.

Unlike standard PCBs, you can not make an RF printed circuit board with one layer. The lowest layer you can use to build an RF PCB is two. And the highest number of layers that you can use in your RF PCB design is 20.

Incorporating vias in the RF PCB makes the transmission more effective between the layers.

Types of Vias

Using at least two vias for each transition point is the most effective mechanism of using vias.

For effectively designing our RF PCB, you ought to follow some design considerations. Here are the references you should follow:

Dielectric Constant

The Dielectric dynamic constant of a material indicates how much electrical energy you can store in an electrical field.

You must find out the frequency ranges of the material you will use. The testing method and available values for frequency ranges also should be considered. You should also consider the conditions of the application you are designing for.

Coefficient Of Thermal Expansion or CTE

From this, we can determine how much an object will change its shape in the changing temperature. It is crucial for both assembly and drilling of the RF PCB. You will use different materials with different CTE rates while designing your RF PCB.

The upper layer should grow faster than the lower layer. If by any chance, the opposite happens, that will destroy the balance of the board.

Loss Tangent

For lower frequency design, you don’t have to consider this factor, but when you are designing for high-frequency, you have to take it seriously.

You have to determine the loss tangent from the material’s molecular structure you will use in the manufacturing process. Materials can be burned off with heat at high frequency. You can overcome this problem by making the components dense.

Spacing

In RF applications, spacing can be a complicated process for skin effect and crosstalk. In crosstalk, boards can be responsible for coupling. And additional heat can be generated for skin effect.

There are many reasons that can create such problems, such as trace length and width. You can minimize the distance to resolve this issue.

Moisture Absorption

This is based on the device’s surrounding environment. If the board you are designing will stay in an air-conditioned room, there is no need to worry. But if the device can face a variety of environmental fluctuations, that should be a top priority in your design.

Performance Vs. Cost

You can find materials with a high-performance quality, but the price is also too high. You have to balance between the cost and performance of your RF PCB design.

This number describes how an object will change in different thermal conditions. You can also measure the thermal robustness from CTE, which significantly impacts the assembly and drilling stage.

In multilayer boards, there must be different materials with multiple CTEs, and some layers must grow quicker than other layers. Any misplacement here will endanger the board’s stability.

The use of FR4 in the RF PCBs is controversial and considered less effective. FR4 is not capable of handling the temperature that high frequency can produce. Moreover, the loss tangent of FR4 is the worst among materials used in RF PCB.

However, some manufacturers suggest that you can use FR4 for those devices that won’t be exposed to high frequency, but still, many engineers disagree with that.

You can not complete a board without using bonding materials. There are many bonding materials that you can use for your RF PCB.

LCP and Ceramic-filled PTFE these two bonding materials are used in some RF PCBs. FEP is another bonding material you would see in many RF PCBs.

Before choosing your bonding material, you have to consider several factors, such as low lamination temperature, re-melt temperature, etc.

Manufacturers prefer both LCP and FEP for their low laminate temperature and lamination. The worry of thermal stressing and soldering are gone with these two materials.

Looking for something more robust? There is a ceramic-filled PTFE for you.

You would find a lot of software for designing your radio frequency PCBs. We can recommend Altium, but there are many, and you can choose any from them.  RF PCB software should provide all the necessary tools and options to design RF PCBs perfectly. Intelligent software will help to reduce the time you have to spend designing the PCB.

Before picking up an RF PCB, you should consider the following:

• First, you have to consider the material’s impedance stability.
• You have to consider the signal loss tolerance.
• The operating temperature of the board is also a crucial consideration. You should consider both the stability and temperature expansion under different temperatures.
• The heat sinking ability is also a vital consideration point.

Yes, you can use them for high voltage devices.

RF PCB’s substrates are not built with FR4 like the other standard PCBs. PCB can not sustain high temperatures.

The substrates of RF PCB are built with many considerations, including dissipation factor, dielectric constant, electrical strength, coefficient of thermal expansion, and thermal coefficient.

RF PCBs are in high demand these days. The ever-changing modern technologies are responsible for this increasing demand. And the demand will not decrease in the near future as the technology is evolving more and more.

Therefore, this is high time to invest in RF PCBs. But not every manufacturer is capable of producing high-quality and efficient RF PCBs because of their complexity. We are a leading radio frequency PCB manufacturer in China and deliver quality RF PCBs all over the world.

Want to learn more about RF printed circuit boards? Just tell us what you want to know. Our PCB experts will answer your every question on demand.