RF PCB Design

For a successful Radio Frequency (RF) PCB manufacturing process, you should adopt strict design, fabrication and assembly procedures.

It is the only way to avoid possible crosstalk, maintain signal integrity, prevent possible component failure, and many more.

Today’s guide captures all the basic and advanced aspects of RF PCB design and fabrication.

Let’ get started.

RF PCB Design Basics

RF PCB

What is Radio Frequency Printed Circuit Board?

We can generally define RF PCB as printed circuit boards designed to operate on medium to extremely high frequencies.

Any high frequency printed circuit board which operates above 100MHz, therefore, falls in the category of radio frequency PCB.

However, when talking about RF PCBs, the actual frequency range of reference is usually from 300MHz and above.

RFs PCBs operating above 2GHz are known as Microwave PCBs.

PCB Design for RF Applications

There are several applications that depend on RF PCB design.

You can attribute this to the unique capabilities that the RF PCBs have. Here are some of these applications.

i. Security Systems

Radio Frequency circuit boards are widely used in security systems and devices.

RF security system

These devices usually depend on RF PCBs for effective functioning and endurance to fluctuating thermal and environmental conditions.

This helps in ensuring that security is not compromised regardless of the environmental or thermal condition.

Devices such as full body scanners, backscatter scanners and metal detectors use RF PCBs.

ii.Communication Industry

Radio frequency printed circuit boards are also able to sustain high bandwidth transmission of data systems. This makes them a favorite in the communication industry.

RF PCBs are also used in the manufacture of remote controls which aid in wireless communication.

Communication satellites are also manufactured using RF PCBs. Usually, they are used in conveying information in thermally and environmentally unfriendly conditions.

With RF PCB, there is the assurance that such fluctuations will not affect performance.

Another common area of application of RF PCBs in this industry is in the manufacture of smart-phones

 iii.Consumer Electronics

Radio frequency circuit boards also come handy in the production of consumer electronics. This is mainly due to their thermal and electrical performance.

Again, RF PCBs tend to be comparatively cheaper, hence affordable to most consumers.

Devices such as smartphones, smart watches, microwaves and radios are manufactured using RF printed circuit boards.

Microwave

iv. Military Applications

Military applications are often exposed to fluctuating weather and thermal conditions. As such, RF PCBs are widely used in their manufacture.

This preference is based on its ability to endure thermal and environmental fluctuations.

Military communication equipment

Such military applications include satellites, radio phones, security scanners, military planes and vehicles.

v.Medical Applications

Radio frequency PCBs have time over been used in the medical industry. Usually, medical devices such as x-ray machines and medical scanners are manufactured using RF PCBs.

The same can be said of medical implants such as pacemakers.

X ray machine

vi.Automotive Industry

Motor vehicles need improved electrical performance. The automotive industry is also regulated to ensure that it complies with the set manufacturing standards.

RF PCBs makes these set standards achievable.

Fully automatic vehicles assembly plant

vii.Industrial Applications

In the industries, there is usually the desire to manufacture effective and dependable products.

This means that the demands for products that can endure both thermal and environmental fluctuations are high.

RF PCBs effectively meet these conditions.

RF detector

In short, all these electrical electronic gadgets use RF PCB circuits to transmit signals.

Benefits of RF Printed Circuit Boards

That these PCBs’ design uses high-frequency materials gives them several advantages for MHz and GHz applications.

It is because of the following benefits that RF PCBs are ideal for applications like military radar, telecommunications, and computer networking systems.

RF printed circuit board

• Stable PCB structure-they have a PCB structure that presents excellent stability, even in high-temperature environments. They can operate at up to 40GHz when working with analog applications.
• Low loss tangent- Because of the low loss tangent and stable dielectric constant (Er), high-frequency signals can travel through the PCB with minimal impedance and at high speed.
• Lower Assembly costs-Because of the possibility of developing a multilayer board stack-up, the materials are easily combined in one stack-up. This leads to smaller and less-costly PCBs that have optimal performance.
• these PCBs, multiple boards can easily be aligned in a complex layout.
• Assembly of fine pitch components onto the board is also easy

Challenges in RF Printed Circuit Board Design

The following problems are common when designing RF PCBs, calling for a lot of preventive work during the design process.

• Sensitivity to noise-RF PCBs incur ringing and reflections. You will, therefore, need to treat them with utmost care
• Impedance matching-high frequency PCBs are known to have minimal tolerance, thus necessitating the need to control the impedance. This is especially necessary for larger trace lengths.
• Return loss-return signals can be a big problem, especially for high microwave frequencies. It is essential to have a good design for the PCB that considers this.
• This is to ensure that the return signal does not go through power planes or the multilayers. If this happens, impedance control is hampered
• Crosstalk-Crosstalk is another common problem for RF PCBs. This problem is usually worse when the board density is higher.

RF PCB Layout Guidelines

RF PCB Design

RF Transmission Lines

The impedance transmission lines are useful for transferring power to and from IC pins.

Here, we will look at the different types, including microstrip, suspended stripline, and grounded lines.

1.Microstrip

Microstrip transmission lines have fixed-width metal routing and unbroken ground plane that is placed on the next layer.

The characteristic impedance will depend on the type and thickness of the dielectric layer. It usually ranges between 50O and 75O.

2.Suspended Stripline

This one is made up of an inner layer and a routing with of fixed width. It has solid grounds over and under the center conductor, usually in the middle of the ground planes or offset.

3.Coplanar Waveguide (Grounded)

When designing RF PCB, a coplanar waveguide helps you to better isolate between RF lines and other signal lines.

It has a center conductor and ground planes on one side. Also, it should have via fences on both sides.

Characteristic Impedance

There are different ways when it comes to calculating and accurately setting the width of the signal conductor line for target impedance.

Only note that the dielectric constant for the outer laminate layers is usually lower because of lower glass content.

You should, therefore, be cautious when entering the dielectric constant of the layers to achieve an optimal balance.

Corners and Bends

The corners and bends of the transmission lines should never be at right angles. All cornered transmission lines should have rounded edges.

Sharp (right angle) cornered transmission lines are prone to higher losses.

The bend radius for the round edges should be at least 3 times the width of the center conductor. This helps to ensure steadiness of impedance while current passes through the bend.

In cases where, for whatever reason, you cannot come up with a curve, you can use an angled meter to reduce impedance fluctuations.

Layer Changes for Transmission Lines

To help reduce inductance loading, use at least two via holes for every transition of a transmission line between two layers.

Use the largest diameter via compatible with the width of the transmission line.

You can as well use three vias if you are not able to use the largest diameter vias due to space limitations.

Signal Line Isolation

Keep the transmission lines as far apart as possible. Never route them close to one another for long distances as that can also increase coupling.

Ensure there is a ground plane to keep apart any lines that cross on separate layers. Keep away high-power signal lines from all the other lines.

Ground Planes

Use a continuous ground plane for layer 2. Strip lines and offset striplines will require that you have ground planes over and below the center conductor.

Do not use these planes for signal or power nets.

If you have to use partial ground planes, they must be below the components and transmission lines.

Never break ground planes or place them under the transmission lines.

To avoid ground return paths that can cause parasitic ground inductance to increase, add enough ground vias between layers.

This will also help in preventing cross-coupling.

Selection of Decoupling or Bypass Capacitors

Any capacitor operating above the self-resonant frequency (SRF) is inductive.

They, therefore, cannot be effective in decoupling. SRF means the capacitors have limited capacity ranges.

If you need broadband decoupling, use many capacitors with higher capacitance.

Bypass Capacitor Layout Considerations

The parasitic inductance on the AC ground path must be minimized because the supply lines must be AC ground.

Parasitic inductance usually occurs based on the choice of component orientation.

Grounding of Shunt-Connected Components

An example of these components is a power-supply decoupling capacitor.

For each of these components, use more than one grounding via to reduce the impact of parasitic inductance. For a collection of shunt-connected components, you can use via ground islands.

RF PCB Design Considerations

From the onset, you must have realized that RF Printed Circuit Boards are quite different from the other types of PCBs.

They rely on special materials and special considerations, as outlined below.

RF Printed circuit board

1)Scaling

As the PCBs are cured during heat lamination, the internal layers will lose quite some mass. Because of this anticipated loss, it is crucial to scale up the circuitry by a certain percentage.

This ensures that when the layers lose weight, they come to their desired dimensions.

The high-frequency materials used in RF PCBs usually behave differently. This means scaling is very difficult because you will need to understand the specific material.

Calculating the scale factor for the particular material that you are using is a challenge that you have to take.

Failure to do this, you will end up with boards with bad registration from drill to pad and layer to layer. Such boards will not perform correctly.

Over time, however, you should be able to determine consistent scale factors for the materials, making it easier.

2)Surface Preparation

PTFE types are very sensitive when it comes to multilayer surface preparation.

A very aggressive preparation can deform the material because it is relatively softer. Significant deformation will render the PCB scrap.

During deburring, the substrate can end up getting polished, which badly affects adhesion. It requires that you always anticipate the need for special handling.

3)Hole Preparation

Because of the different nature of the materials used in RF PCB, you will need to use different methods in hole preparation.

Therefore, you must adjust drill machine parameters to ensure there is no surface smearing.

Again, different gases than the usual ones are used in treating the holes after drilling. You must, therefore, plan all the necessary steps to ensure that the holes will come out clean.

4)Thermal Expansion Rates

If you are designing a hybrid multilayer PCB by combining high-frequency materials with FR4, you must properly match the materials.

This is because if the material characteristics fail to match, the expansion rates of the layers will be different.

You will also need to match the hole fill materials you use to plug the vias with the other materials in the stack.

If you are an expert designer and fabricator, this should not be a big problem. You have most likely had to analyze these material characteristics before.

5)Machining

The behavior of RF materials when subjected to different machines usually differ from FR4 laminates.

During drilling, for example, ceramic impregnated materials can prove very hard on drill bits.

In such cases, the RPM and spindle infeed should be customized based on the specific characteristics of the material. This will also help you to avoid fibers that usually remain inside the hole walls

To avoid poor quality of the edge, use special bits that are developed for RF laminates. If you use a wrong type of router, the tool is likely to pill against the board’s fibers, giving it a furry edge.

V-scoring may also damage the RF material, and is not recommended unless very necessary. The blade of the v-scoring machine is likely going to pull off the copper from the surface.

6)PCB Material

As we already saw in the earlier sections of this guide, RF PCBs are very “choosy” when it comes to base materials.

Materials such as FR4 are of very low quality when it comes to manufacturing RF PCBs.

The danger with choosing the wrong material is that the problems are mostly realized after production, leading to extreme losses.

If you are hiring a PCB manufacturer, you may have to inspect samples if you doubt the choice of materials. Otherwise, you risk getting a whole order of scrap.

7) Choice of Transmission Line

Choosing the right transmission line is critical for the performance of your RF PCB.

There are two main options when choosing transmission lines for RF PCB: Grounded coplanar waveguides (GCPW) and Microstrip.

If your design is more compact, a GCPW will give better performance because:

• They are characterized with unbroken ground plane
• The grounded layers enable greater isolation for transmission lines. This minimizes losses and reflections.

Despite these strengths, most designers prefer microstrip because most programs do not support the GCPWs.

8)Dimensions of the Transmission Lines

The dimensions of the transmission lines usually affect PPCB performance. All transmission lines and components should be at an impedance of 50 O or very close thereabout.

Again, using very thin transmission lines are likely to lead to lousier performance.

9)Via Spacing and Placement

Via spacing must always be appropriate because the vias are essential for RF PCB performance. It is the vias that help in reducing ground inductance in the RF PCB.

They also help in solving the problems that come with unwanted coupling.

10)Routing on Bias and Ground Layers

In RF PCB design, the system bias layers’ return current path should be well checked.

Signal layers between bias and ground layers lead to larger return paths. This causes noise coupling on signal layers.

For a good layout, there should be no signal line between the ground layers and the bias.

RF PCB Design Software

As an RF or microwave design engineer, designing a well-functioning RF PCB can be such a difficult task. What you don’t want is to finish the long and tedious process, only to realize you have to start it all over again.

Well, the secret is in automation, and you will need to get the correct software for the job. Below are some of the best tools to help you with great RF PCB design.

 PCB Designs software

· Advanced Design System

ADS is mostly considered the leading software for RF PCB design. It is highly popular because of the simple interface and highly innovative technology.

Because of these strengths, ADS is used by most leading communication, networking, aerospace and defense companies to design RF PCBs.

·Microwave Office

This is another design software with a very interactive interface.

It comprises an integration of very innovative tools and technology with the partner company’s tools (specific to the particular application).

The result is a superb software system that easily produces highly-frequency designs. It is fast emerging as the future of RF PCB design.

·Altium

Altium is widely considered as one of the most stress-free PCB design software. It incorporates engineering and PCB design tools into one interface, thus simplifying the entire process.

Altium designer enables a smooth and coherent flow from the concept development, to designing the PCB.

It guides a smooth process all the way through 3D modeling until you have the final manufacture.

The clarity and coherence are critical in RF design to avoid making even the slightest mistake. Remember, RF PCB design requires accuracy because any simple mistake leads to a huge loss.

Altium also allows gerber file like reviews on the PCB files.

· Ansoft Designer

The special feature about Ansoft Designer is that it enables a hierarchical and direct simulation of complex distributed networks. This leads to a circuit like (in functionality) high-frequency design, leading to excellent RF PCBs.

·Eagle

Eagle is a very popular PCB design software, especially for the other common PCB types. It has a well-organized set of tools, including a schematic editor, layout editor and the autorouter.

This enables a highly integrated PCB design process.

The list of design software that you can use to design RF PCBs is a long one. Apart from the ones we’ve discussed above, others are:

6. KiCad
7. Autocad
8. OrCard
9. MATLAB
10. Micro-Cap
11. Calibre
12. HSpice
13. Microwave Soft
14. S-Edit
15. L-Edit
16. HFSS
17. Cadence
18. Electronic Workbench

As you can see, there are several software options to choose from. So how do you choose which one to go for?

A good PCB design software is that which is easy to use. Consider going for widely used software to enable easy collaboration with other players in the industry.

Although some software options are very expensive, some cheap, while others even come free, price should not be the main factor.

It is also critical for you to ensure that the software enables you to review the files once you are through with the design. To achieve this, the storage format must enable such reviews.

Gerber files enable you to visually review key aspects of your RF PCB design, such as the transmission lines.

Programs such as ViewMate also allow you to review the files.

RF PCB Material

RF PCB Material

There are a number of factors you must consider when choosing an RF PCB material. They include:

Important Characteristics

RF PCBs are quite different from the other PCBs. This is especially evident in the special materials that you will need when making RF PCBs.

Before we look at these materials, let us first focus on some critical characteristics that they need to have.

·Dielectric Constant (Er)

This refers to the measure of the ability of the material to store electrical energy in an electric field.

The axis of the material affects the dielectric constant (Er) because Er is direction-dependent.

The range of frequency under which the material is tested is usually very important. This, together with other factors at testing, must always match those of the target application.

·Coefficient of Thermal Expansion (CTE)

Simply put, CTE explains the impact of temperature change on an object’s size. CTE is therefore very important when the board comes to the drilling and assembly stages.

This is because accuracy is very important during the positioning of the holes and components.

A slight change in the size of an individual material in the stack can lead to a huge alignment error.

Materials such as PTFE can smear during drilling if the heat is too much.

A material with poor CTE can prove very costly because it can break at the latter stages of production like component soldering.

Manufacturers prefer materials with lower CTE because they are able to handle the heat during drill and assembly.

·Loss Tangent

Loss tangent is usually highly dependent on the molecular structure of the base material.

While it is not always an issue for the low-frequency PCBs, loss tangent is a critical consideration for RF PCBs.

This is because there is always signal loss as the frequency increases.

Complex multilayer PCBs are even more sensitive. They generate additional heat during operation, which needs to be controlled to avoid losing frequency.

·Moisture Absorption

Always consider the working environment of your intended device. PCBs for devices designed to work under water or high moisture environment will need special characteristics to counter the implications.

·Cost vs. Performance

Whereas the other characteristics are of critical importance, it is always necessary to balance between the performance and the cost.

Always try to get what is affordable, while ensuring that the material meets your needs for Er, CTE and Loss tangent.

Common RF PCB Materials

Having looked at these characteristics, which are the most common materials for RF PCBs?

In most cases, RF PCB materials are achieved by combining PTFE, certain forms of glass, hydrocarbons and ceramics.

·PTFE with Woven Glass

One of the best quality combinations usually comprises of PTFE with either woven glass or microglass fiber.

However, this combination is more costly, and only goes where the pursuit for quality far much outweighs cost considerations.

Despite having great electrical properties, it has a high CTE, which is a weakness.

PTFE with microglass fiber or woven glass has excellent electrical properties, but a high CTE.

·Ceramic-filled PTFE

A combination of PTFE and ceramic comes at a relatively lower cost but is still of good quality.

This is primarily because manufacturing RF PCBs with this material is easier than the PTFE-microglass combination.

This option comes with the strength of good electrical characteristics. It also has low CTE, meaning it is thermally stronger.

This material usually has a lower moisture absorption rate as opposed to when woven glass is added, which increases moisture absorption.

·Ceramic with Hydrocarbon

Another simpler to manufacture option is ceramic that is filled with hydrocarbon. It has the benefit of having very low CTE.

However, the resulting PCBs are usually characterized by weaker electrical characteristics and present less reliable signals.

PCBs made from PTEF ceramic with hydrocarbon presents just a slight increase in moisture absorption. This means it is a better choice if you aim to strike a balance between cost and moisture resistance.

The most important aspects that you will to consider when selecting one of these options include price and electrical performance.

However, if there is going to be soldering stress at the assembly stage, then thermal robustness is critical.

This also matters a lot if the device is destined to work in environments like the aerospace industry, which are very demanding.

·FR4

This is a very common material, but equally a controversial one when it comes to manufacturing RF PCBs.

It is mostly regarded as absolutely unsuitable for RF PCBs, although some manufacturers think it should be given a chance.

When it is the only available, affordable option, it may be considered. Still, you should expect that it may only function for RF PCBs meant for very low frequency applications.

Although FR4 is very cheap compared to the other materials for RF PCB, it is less likely to achieve good performance.

Its loss tangent is obviously going to be an issue, making it inappropriate for high-power applications.

Component Sourcing for RF Printed Circuit Board Design

The first step in RF PCB component sourcing is the preparation of a bill of materials (BOM). This is a well-detailed list of all the components that you will need in the manufacture of your RF PCB.

BOM

Include the part numbers in the list and information on the manufacturer of each of the parts. This will give you a clear insight during the whole process.

Normally, you may not be in a position to manufacture all these components on your own. As a result, you will have to outsource them from the manufactures.

Manufactures depend on your BOM to get you the components that you need for your RF PCB.

Component sourcing

·Considerations in RF PCB Components Sourcing

When outsourcing from a manufacturer, there are a number of factors that you will have to put into consideration.

• First, assess the services offered by the manufacturer.
• You should also evaluate the expertise of the manufacturer. In most cases, having qualified staff are indicators of expertise. This assures you of flawless components.
• You may also have to look out for the experience that the manufacturer has had in the fabrication of RF PCBs. With such a manufacturer, you will be assured of fewer difficulties when outsourcing from them.
• Another vital factor to look out for is certification by the authorizing bodies. Certification implies compliance with the set standards. As such, you adequately are assured of the quality of components that you are buying.
• A good component manufacturer or supplier should also be able to give you the appropriate quotation for the materials needed. The manufacturer will be guided by the bill of materials presented.
• Shipment-Usually, components are delicate, and they require specialized transportation. Manufacturers that pack and ship components are likely to consider the safety of the components.
• Warrantee is also another essential consideration.

When all these factors turn out to be positive, then you are assured that the components sourced will meet your needs.

·Precautions when Sourcing for RF PCB Components

There are also quite a number of precautionary measures that you should take when deciding on the manufacturer to source components from.

• You should first avoid making a rushed decision when choosing the manufacturer. A rushed decision is likely to hamper your analysis of advantages and disadvantage from the list of manufacturers.
• You will be taking too much risk if you fail to make the objective of the project clear. When sourcing for the RF PCB components, what you intend to make out of the PCB must be clear.

If this is not done, then the manufacturer is likely to exclude some components or add irrelevant ones. This will ultimately lead to flaws in the final application if the wrong components are used.

• When outsourcing, it is also important that you trust the manufacturer with the production. This means giving them the freedom to be innovative enough when getting you the components. As such, when there is no trust, then there is no need to continue working with a particular manufacturer.
• It is not wise to source for the best bargain. Quality usually comes at a cost.

When the prices are too low, then the assumption is that the quality of the components will be compromised. This will also compromise the general performance of the RF PCB.

• Do your research and ensure that you have a rough idea of the market prices of the components.
• If possible, avoid outsourcing overseas. Usually, the costs tend to be higher when you source for the components overseas. Shipping at times leads to the destruction of the components leading to the poor performance of the RF board.

 Classification of Radio Frequency Printed Circuit Board Design

Radio frequency printed circuit board

There are different types of multilayer printed circuit board, depending on the intended application. Based on the types of RF PCBs that the design intends to come with, RF PCB design can be classified as:

1.Multilayer RF PCB Design

In multilayer RF PCB, the board has more than two layers. The least number of conductive layers in this kind of board is three. These conductive layers are buried in the center of the material.

Usually, you are supposed to do the alternation of the layers of prepreg and core materials. You will then proceed to laminate them together under high temperatures and pressure.

The result will be a multilayered PCB.

This procedure is important because it will help you in expelling trapped air between the layers. It further encapsulates the conductors with resin.

The adhesive holding the layers together are then melted and cured.

There are a number of materials combinations at your disposal when fabricating your multilayered RF PCB. You can use basic epoxy glass or even exotic ceramic.

Another option is to use Teflon materials.

2.Rigid RF PCB Design

Rigid RF PCBs are those that are made using solid substrate material. These prevent the board from twisting hence the term “rigid.”

FR4 stiffener is the most commonly used material in the stiffening process. It is also made up of copper trances and paths.

These are usually incorporated into the single board to provide room for connecting various components.

Traditionally, these rigid RF PCBs are the most commonly used compared to their flex PCB counterparts. This is mainly informed by the costs involved in using the latter.

Rigid RF PCB design requires the use of appropriate design software. Some preferred options here are Altium, Proteus, or EasyPC.

Rigid RF PCBs are composed of a number of layers. These layers are combined using heat and adhesive. This gives the board a solid shape.

The substrate layer is made of fiberglass. Note that additional heat will be required to laminate the copper layer onto the.

For insulation purposes, the design must incorporate adding a layer of solder mask above the copper layer.

Also, add silkscreen above the solder mask layer.

3.Single-Sided RF PCB Design

This is the simplest form of RF PCB board. The design has only one conductive material.

Single-sided PCBs are usually preferred for low-density designs.

Remember there is no plaiting through the holes on this board.

Single-sided RF PCBs mainly use materials for single-sided RF PCB include FR4, Aluminum and Copper base.

4.Double-Sided RF PCB Design

In this type of RF PCB, there are two conductive copper layers. This means that the board is designed with traces or paths on both sides. It means there is a connection between the two sides.

This is made possible by the holes that are drilled on the board. Mounting of components onto the board are done using through hole technology and surface mount technology.

This design provides for the lamination of layers on both sides of the board.

Glass epoxy resin is used as an insulating material at the base of the design. Copper foil is also laminated onto either sides of the substrate.

For protection, you will need to have soldermask above both sides of the RF PCB design.

RF Printed Circuit Board Manufacturing Process

Below is an elaborate outline of the entire process of RF PCB design, from fabrication, assembly, to quality tests.

Step 1 PCB Design and Layout

The design marks the first step in the manufacture of RF PCB. First, design the layout for the RF PCB. The design can be emulated from the prototype using one of the RF PCB design software we have already discussed.

Step 2 Production Preparation

Cut Lamination-From the design, proceed to cut laminate in the same size as the board or the panel’s size.

Drying

The drying is done to prevent the board from warping when processing. This should be done at around 150? for about 3 to 4 hours.

Step 3 Inner Layer Imaging

Inner Film

Apply a dry film to the bare copper core board. Proceed to perform photo imaged reactions on the dry film.

Inner layer development

When this is done, you will have exposed the core plate. The dry film that had not been exposed before is revealed. This will reveal the original copper skin exposing retained dry film. Use photo-imaging in this step.

Step 4 Inner Layer Etching

Etching

Through the etching line, you will be able to protect the copper skin with a dry film. Proceed to etch away copper skin that is not protected by the dry film. This will expose the patterns that are supposed to be retained.

Unloading the film

Proceed to retreat the dry film of the copper sheet on the core board. When this is done, the line pattern that should be retained will be formed.

Step 5 Inner Layer AOI

Automatic optical inspection is the first inspection step. It will enable you to check whether there is short-circuiting or opening of the core plate. It will also help you in inspecting whether the etching is clean or not.

Step 6 Lamination

Use an insulating medium to press copper foil to one board in between the layers.

Step 7 Drilling

Proceed to drill the laminate plate. At the time of doing this, there should be no metal in the hole. This helps in ensuring that the layer is not connected to another layer.

Step 8 Electroless copper deposition

Next, coat the hole with a very thin layer of copper. This is achieved through a chemical reaction.

Step 9 Horizontal Electrolytic Plating

Use electrotransfer reaction to thicken the hole. The thickness should be between 5-8µm. This is made possible owing to the existence of an already thin layer of metallic copper in the hole.

Step 10 Outer Layer Imaging

Outer Layer Film

Onto the bare copper core board, apply a dry film. This dry film is necessary for performing all photoimaged reactions.

The difference between this inner layer and the outer layer is the drilling on the plate. Attachment of the dry film to the plate will offer protection to the hole.

Outer layer development

After you have developed the inner layer, the copper that is under the dry film is retained. However, after the outer layer’s development, it is etched. The copper that should be preserved is then left exposed.

Step 11 Graphic Plating

Thick copper plating

Plate the bare copper to the finished copper thickness. This thickness should measure between 18 and 25µm.

Ensure that you plate the surface of the copper thickness and the copper holes thickness together. You will have achieved the recommended copper hole thickness.

Tin plating

To protect the copper foil, proceed to thicken copper’s surface with a layer of white metallic tin.

Getting rid of the film

You can now get rid of the dry film that is attached to the board. Etch away the copper that is under the dry film.

The tin used in the previous sub-step will help in ensuring that the needed copper is retained.

Step 12 Outer Layer Etching

Etching

Tin will offer protection to the desired copper in this stage. When you etch the line, the copper you had exposed will be etched away. In the meantime, the copper that you had been protected with tin will remain.

Tin Removal

Proceed to remove the tin used to protect the copper. As a result, the copper intended to remain will be exposed. At this point, all outer patterns will have been completed.

Step 13 Solder Masking

Deep the panel into the liquid soldermask. Proceed to expose the board to high-intensity ultraviolet rays.

The application of soldermask is done to offer oxidation protection to the copper circuitry.

Step 14 Silkscreening

In this step, you will be printing information on the board. This makes it a crucial step in PCB manufacturing.

Step 15 Surface Finish

This step will ensure that the board’s surface is protected and can be soldered.

After the profile process, you can also opt for other surface finish processes. These include V-CUT and gold finger.

V-CUT

In this option, you will cut the panel into specific sizes and shapes, depending on the intended applications of the board. You can achieve this using a router or a v-groove.

When you intend to leave small tabs, then a router is the best option for you. V-groove, on the other hand, will enable you to cut diagonal channels on either sides of the board.

Gold Finger

This simply refers to plating connectors using gold. As such, the durability of the edge connectors will be assured. This goes a long way to protect the RF PCB from malfunctioning.

Step 16 Electrical Testing

It is important to conduct electrical tests on the board. This will help you in ensuring that it is functional.

Usually, there are two main tests done: isolation tests and circuit continuity tests.

Step 17 Final Visual Inspection (FQA&FQC)

After the fabrication process, visual inspection can be conducted on the finished RF PCB.

If a correctable anomaly is detected, it is corrected. Otherwise, if the anomaly is adverse, the board is discarded. This will help in ensuring that the intended applications function effectively.

RF PCB Design Quality Standards and Regulations

Some many standards and regulations govern the design of RF PCBs. By observing these standards, manufacturers globally are able to arrive at quality RF PCB designs.

It also enhances the compatibility of the design with the components and production procedures of relevant companies.

Some of these standards and regulations are:

Quality inspection process

§CGMP

When identifying a manufacturer of RF PCB, one of the quality standards to check out on is CGMP.

CGMP stands for Current, Good Manufacturing Practice regulations. It is a set of regulations that are set by the Food and Drug Administration.

As such, these regulations ensure that the design of your RF PCB is monitored. It also regulates the manufacturing processes and the facilities within which the production process is done.

When designing an RF PCB, you will have to comply with these standards.

§IEEE

This refers to the Institute of Electrical and Electronics Engineers.

It is a professional society that promotes the development and even application of electrotechnology.

Subscription to this body will enable you to use current technology in RF PCB design and manufacture.

§CE

This is the mark of certification in the European Economic Area. It ensures that your RF PCB design complies with a number of set standards.

It also the quality of components that are manufactured in or imported for use in the EU region

As such, they include health standards, user-safety standards, and even environmental protection standards.

When purchasing components for your RF PCB within the European market, ensure that they bear this mark.

Components manufactured out of Europe but due to be sold within the community also bear this mark.

§RoHS

This standardization mark restricts hazardous substances. It is largely used in the European Union.

It is more focused on restricting the use of hazardous substances on both electrical and electronic products.

The validity period for this standardization mark is five years.

Restrictions are imposed against products such as led, mercury, chromium and cadmium. PBBs and PBDEs also restricted.

Your design must be restricted within the confines of these rules.

You will also have to check on this standardization mark before you get to purchase components of RF PCB.

This is a universally accepted standardization mark, so you should expect it on most products.

§ CCC

This refers to the Chinese certification mark. It is a mandatory mark for products that are imported and sold or even used in China.

When purchasing your RF PCB components from China, check out this mark to ascertain quality standards.

§ISO

ISO 9000 is a standardization mark to aid organizations in making sure that consumer needs are met.

As the needs are being met, quality is expected to be at par with the set production regulations.

It is one of the most common standardization marks. This certification on the company and the components you are purchasing is a confirmation of quality.

§ASTM

This is also an international standardization organization. Its function is to develop and make publications of mutually agreed standards for both materials and products.

This also applies to systems and services.

Check out on the components of your RF PCB to be assured of a quality product.

Conclusion

RF Printed Circuit Boards are an exceptional category of PCBs, going by the materials used and the unique design requirements.

This is because of the frequency requirements that make them undesirable for common materials and designs.

After going through this guide, you now know what informs all these special characteristics.

You are also well versed with all the guidelines and considerations for RF PCBs.

You can always check here for more elaborate guides like this.