The demand for RF PCB is growing in the electronics industry. PCBs have been existing for a while now. They remain the core material used in electronics production. There are different types of PCB and the RF PCB is one of them.
RF PCBs have got some unique features that make them relevant in the electronics industry. A lot of electronic devices use RF PCB. In this article, we will discuss the essential facts you should know about RF PCB. This article aims to give answers to questions like what is RF PCB? What is RF PCB design? What are the properties of RF PCB? Why is it important in electronic manufacturing?
What is RF PCB?
RF PCB means Radio Frequency Printed Circuit Boards. This is a type of circuit board that operates at a higher frequency than other types of PCBs. RF PCBs operate above 100MHZ. This board operates at high frequencies. A radio frequency PCB is commonly used in applications that require high speed. Since these circuit boards have a higher frequency, they are more complex to design.
RF board has a frequency that usually falls between 300 MHZ and 3GHZ. If the frequency range is above 2GHz, it is a microwave PCB. Therefore, RF PCB manufacturers can’t use FR4 boards for the production of this board. The production of RF PCB requires the use of special materials. RF circuit boards are suitable for use in applications like sensors, wireless controls, and more.
In today’s world, more new technologies use RF PCBs. New technologies like robotics also use RF PCBs. The manufacturing of RF PCBs is a very complex one. These boards need to be fabricated with high-quality materials. Therefore, a professional PCB manufacturer is required.
RF PCB Materials
RF materials are a combination of hydrocarbon, ceramics, and PTFE. The most common material for RF PCB is PTFE with woven glass. This is a perfect combination when quality is necessary. However, if budget is a concern, ceramic-filled PTFE is a better option. This material is much easier to produce and as such, reduces cost.
It is important you also consider thermal robustness as a determinant. This will be a huge concern for applications that expose devices to fluctuating temperatures. Ceramic-filled PTFE features a low CTE and excellent electrical properties. PTFE with woven glass also features great electrical properties but has a high CTE. Ceramic-filled PTFE is a more preferred option due to its properties.
Ceramic -filled hydrocarbons also feature a low CTE. As regards moisture, PTFE ceramic features a low moisture absorption rate. However, the moisture level rises when woven glass is used. RF PCB manufacturers can add hydrocarbons to PTFE ceramic. This can increase moisture absorption and as such, balancing cost and resistance to moisture.
FR-4
FR4 is a common material in the PCB industry. This material has some controversies as regards its use. There are mixed reactions about FR4. However, this material remains the cheapest option for RF PCB. Some engineers disregard it as an ideal material for RF. The loss tangent of this material is poor. Therefore, it isn’t an ideal option for broadband or high-power applications.
Bonding materials
These materials make a board complete. LCP, FEP, and ceramic-filled PTFE are examples of bonding materials. Most times, materials with lower lamination temperatures are ideal. LCP and FEP feature lower lamination temperatures and lower re-melt temperatures. There are some ceramic-filled PTFE materials with higher reflow temperatures. These materials are ideal for more thermally robust applications.
Properties To Consider When Choosing RF PCB Material
RF PCBs feature some properties that make them ideal for use in some applications. This circuit board works beyond a particular frequency. There are some properties responsible for this. These properties are responsible for the performance of RF boards.
Coefficient of thermal expansion
CTE measures how the size of a material changes with temperature. The coefficient of thermal expansion measures the thermal robustness of a circuit board. This measurement plays a significant role in the assembly process of PCB manufacturing. Some materials experience changes in size at different temperatures.
PTFE is a good example of a material that can smear at drill if the temperature is hot. Material with high CTE can result in a broken board during the final stage of the PCB production. Therefore, a material that features lower CTE is best used for RF boards.
Moisture absorption
This is another important property an RF PCB material should have. The ability of the material to tolerate moisture is a huge concern. However, the type of environment an RF device will be operating matters. If the board will be indoors, you don’t have to worry. But, if the board will be exposed to several environmental conditions, a material with low moisture absorption is ideal.
Dielectric constant
This refers to the ability of a material to save electrical energy in an electric field. The dielectric constant of a material always depends on its direction with the axis. It is very important one understands the material’s frequency range.
Spacing
Skin effect and crosstalk can make spacing complex in RF applications. Crosstalk refers to when the board interacts with itself. This results in signals bleeding into components. The skin effect happens when a trace’s resistance begins to rise, resulting in resistive losses. Factors like trace length and width can cause this. The best way to address this problem is to minimize distances.
Loss tangent
Loss tangent is an essential property in RF material. This is a major concern for high-frequency designs. The molecular structure of the material determines the loss tangent.
Applications of RF PCB
An RF PCB has some unique properties. This type of PCB is ideal for use in high-frequency applications.
Security systems
RF PCBs are commonly used in security systems. Security devices often feature RF PCBs. This is because of their effective functioning and resistance to varying environmental conditions. RF PCBs can withstand any thermal or environmental condition. RF PCBs play a vital role in the manufacturing of security devices. Backscatter scanners, metal detectors, and robotics feature RF PCBs.
Wireless technologies
RF PCBs are present in remote controls. Wireless applications depend on RF boards to help transmit commands. Walkie talkies, TV remotes, and more feature RF PCBs. These devices receive and transmit data and as such use, RF PCBs.
Communication industry
RF PCBs are very essential in the communication industry. For example, communication satellites feature RF boards. Satellites help convey information in any type of environment. With the use of RF PCBs, environmental fluctuations won’t impact performance.
Sensors
These days, sensors are commonly used in different applications. Automated gates and doors have become the order of the day. These doors can’t function without sensors. RF PCBs are used in the manufacturing of these sensors.
Consumer electronics
RF PCBs are ideal for use in consumer electronics manufacturing. Consumer electronics like radios, smartphones, microwaves, and smartwatches feature RF PCBs.
Types of RF PCB Design
Radiofrequency PCBs are available in different types. The intended application of the RF PCB will determine the type to use. It is important you go for the RF PCB type that meets the requirement of the intended applications.
Single-sided RF PCB design
The single-sided RF PCB features one conductive material. This is the simplest type of RF board. This type of board is ideal for low-density designs. These boards require no plating through the holes. The common materials used for this RF PCB type are copper base, aluminum, and FR4.
Double-sided RF PCB design
There are two conductive copper layers present in this RF PCB type. This RF board features paths or traces on the two sides. There is a connection between both sides. For this type of RF, manufacturers use mixed technology to mount components on the circuit board. This RF PCB design uses glass epoxy resin as the insulating material.
Multilayer RF PCB design
There are more than two conductive layers in this type of RF PCB design. These layers are in the center of the material. This design entails alternating the layers of the core materials and prepreg. After that, you will laminate these layers under high pressure. The manufacturer melts the adhesive between the layers.
Rigid RF PCB design
This is a type of RF PCB design that uses solid substrate material. Rigid RF PCB uses FR4 stiffener to make the board rigid. This circuit board features several layers. Adhesive and heat are used to hold these layers together. Doing this makes the RF board solid. RF PCB designers utilize design software for this type of board.
Advantages of RF PCB
RF PCBs have continued to grow popular in the PCB industry. This can be attributed to a lot of benefits they offer. Below are some advantages of RF PCB;
High tolerance power
RF PCBs have the ability to tolerate high power. While some PCBs fail to function in high-temperature settings, RF PCBs function properly. These PCBs were designed to withstand varying temperatures. This is a major reason this rigid flex PCB is used in high-end applications. RF PCBs tolerate thermal stress, which makes them a blessing for most industries.
Faster working capacity
RF PCBs have faster interconnection between materials. Their rapid signal travel makes them work faster than other PCBs. These boards can supply the signal in a circuit quickly.
Cost-effective
RF PCBs are the best way to reduce cost. The multilayer RF PCB helps to minimize the cost of circuits. The circuit cost decreases when the weight and size reduces.
RF PCB Manufacturing Process
The manufacturing process of RF PCBs is a complex one. This process will be discussed below.
The design
This step involves designing a blueprint of the circuit board. The PCB manufacturer can use computer software to achieve this. There are several computer software available to help you create the perfect design. You can get correct details for the external and internal layers by using a trace width calculator.
Design printing
Once the design has been created, the next step is to print the design. You can use a plotter printer for this. The external and internal layers of the circuit board require different colors. For the non-conductive path, you will use clear ink. The black ink indicates circuits and copper traces.
Substrate creation
The next step here is to create the substrate. You can make your insulating material PTFE since it is an RF PCB. This material holds components firmly on the structure. You will have to bypass the materials via an oven. After this, you pre-bond copper on any of the sides of the layer.
Inner layers printing
Here, the PCB manufacturer will print the design on the board. You can use a photo-sensitive film for this process. When you expose this to ultraviolet light, it will become hard. You can arrange the actual print and the blueprints.
Unwanted copper removal
After everything has been done, you will have to clean up unwanted copper on the board. You can use a chemical solution to get rid of the unwanted copper.
Alignment
The PCB manufacturer will use the drilled holes to align the outer and inner layers. The optical punch machine will help you drill the pins via the holes. Doing this will align the layers.
Layers lamination
This process involves fusing the layers. Here, you will use metal clamps to hold the different layers. The first thing that goes into the alignment basin is the epoxy resin layers. After this is the layer of substrate. The copper foil is the next layer and then the epoxy resin.
Drilling
This involves generating holes with the use of a computer drill. These holes will expose the inner panels and the substrate. You will have to remove any traces of copper here.
Plating
At this stage, you will have to plate the circuit board. This can be achieved by using a chemical solution. This solution will help you join all the layers. The circuit board will then pass through different chemicals. Thin copper will pass through the drilled holes.
Outer layer imaging
This step involves the use of a photoresist. You will apply the photoresists on the outer layer. Then the photoresist will harden up when exposed to ultraviolet light. This will help get rid of unwanted photoresist.
Etching
This step involves using a chemical solution to remove unwanted copper under the resist layer. . The unwanted copper is the non-circuit copper. Etching helps to create the copper traces on the board.
Solder Masking
Here, you have to apply a solder mask on the panels. Start by applying epoxy and solder mask film. The green color of a circuit board is a result of a solder mask.
Silkscreening
This process involves printing all necessary information on the board. The fabricator prints the text and graphics on the board using non-conductive epoxy ink. The silkscreen is the uppermost layer of a circuit board. It serves as the reference indicator for mounting components on a board. The information on the board includes symbols, marks, logos, and more.
Surface finish
In this stage, the manufacturer puts a coating between the circuit board and the component. Surface finish helps to shield exposed copper circuitry and ensure solderability. There are different types of surface finish for radiofrequency PCBs. OSP, HASL, and ENG are common surface finish options.
Testing
This is the last stage of the manufacturing process of RF PCBs. A PCB goes through this stage when it has passed through all the steps outlined above. There are different types of testing. Electrical testing, visual testing, and X-ray testing are the common types of testing methods employed by PCB manufacturer.
RF PCB Shielding-What is it?
In wireless technology, most wire becomes a receiver or an antenna. The signals these wires transmit or receive can reduce the general performance of the radiofrequency subsystem. RF PCB shielding techniques can help to reduce electromagnetic interference and provide reliable systems. The use of RF PCB shielding can help to reduce electromagnetic interference (EMI).
Electromagnetic or RF interference is electromagnetic energy that can influence circuit performance. This energy is generated by a part of the circuit and gets to other parts of the circuit through radiated or conducted paths. The major goal of any RF design is to minimize the level of emitted radiation.
It is important to shield critical parts of the PCB to avoid emissions. RF PCB shielding is a kind of conductive barrier housing an electrical circuit to prevent EMI from leaking. Shielding is more cost-effective when you employ other techniques like filtering and grounding.
PCB designers often consider RF PCB shielding as the last option since they can install RF shields when the design is completed. Employ shielding from the start of the design process will help designers to provide a cost-effective system design. The capability of the RF shield to block RF signals depends on a number of factors. The material thickness, the material conductivity, and the material permeability are factors responsible for this.
Furthermore, the conductivity and permeability of the material control the material’s ability to reflect signals. Some shields use apertures in their structure. This enables air to flow through, reducing the buildup of thermal in circuit sections.
What is the Difference between Microwave PCBs and Normal PCBs?
RF and microwave PCBs feature high speed and clear signals. These boards have great thermal, electrical, and mechanical properties. RF/ microwave PCB is ideal for use in wireless circuit applications. The difference between a microwave PCB and other types of PCB is in their properties. Normal PCBs feature RF that ranges between 500 MHz and 2 GHz. An RF PCB features a layout above 100 MHz. While a microwave PCB has a frequency range above 2 GHz.
RF and Microwave PCB design require special material. These PCBs are an innovative circuit board designed to operate within some frequency ranges.
Factors to Consider When Choosing RF PCB Manufacturer
It is very important you consider some factors when choosing an RF PCB manufacturer. Your manufacturer will determine the effectiveness of your board. Therefore, ensure you put some factors into consideration when selecting one.
Experience
Experience indicates how skillful and knowledgeable your manufacturer is. You wouldn’t want to choose a manufacturer with no experience in RF PCB manufacturing. Choosing an experienced manufacturer helps to reduce the chances of failure in your board.
Prototyping
You need to ask if the manufacturer designs prototypes. Prototyping is an important step in the fabrication process. This helps to prevent any loss or mistake in the final PCB.
Cost
Cost is an important factor you should always take into consideration. Ensure you have an idea about the price your manufacturer charges. You can check out the websites of these manufacturers to know more about market prices.
Customer service
Don’t overlook this factor. It is very important. You definitely want a manufacturer that is responsive to your needs. A good manufacturer will work according to your requirements. A good RF PCB manufacturing company should have a good support system.
Packaging and shipping
Ensure you consider this factor. Know the shipping and packaging policy of your manufacturer. RF PCBs require extra care since they are sensitive. They can malfunction when they are not properly handled.
Frequently Asked Questions
Can RF PCBs be used in the manufacturing of high voltage devices?
Yes, RF boards are ideal for use in high voltages applications. The substrate of RF PCBs is produced from FR4 and as such, they can withstand high temperatures.
What is the difference between high frequency PCBs and RF PCBs?
High frequency PCBs feature high frequency signals above 1GHz. RF PCBs feature frequency signals greater than 100 MHz.
Why do manufacturers use filler materials for RF PCBs?
RF PCB manufacturers use filler materials often. This is because they offer extra materials to fill up gaps during RF PCB fabrication.
Conclusion
By now, you should have known much about the radio frequency PCB (RF PCB). This PCB operates at high frequency signals as well as small wavelengths. Any laminate material utilized in the building of Microwave and RF PCB comes with specific characteristics. These include coefficients of thermal expansion, loss, tangent, and dielectric constant. It’s clear that RF printed circuit boards play a very significant role in the electronics industry today. The great news here is that we have covered everything necessary about the RF PCB. Manufacturing one shouldn’t be a problem too. Please contact us if you have any problems.
