With the advancement of technology, the urge for faster data transfer and wireless devices is increasing, leaving behind high-frequency and high-speed signals.
High-frequency signals in a PCB cause signal loss and crosstalk among the signal traces.
A high-frequency printed circuit board helps in reducing signal loss and provides a lower dielectric constant (DK) and dissipation factor (DF). Compared to a standard PCB, high-frequency PCBs provide controlled impedance and robust thermal resistance with a very low coefficient of thermal expansion and water absorption.
You cannot win a sports car race with your average car, though it drives you to the office and helps fulfilling other daily tasks. The Same as the most widely used PCB substrate, FR-4 cannot carry out the desired results for a high-frequency circuit. That is where we need high-frequency substrates to minimize signal loss and enhance performance. A wide range of high-frequency substrates with different properties is accessible. Some materials are more appropriate than others. However, the choice among these materials depends on the electrical specifications and budget of the PCB.
Rogers is a big name in the production industry of high-frequency PCB laminates. The brand produces the best quality high-frequency laminates that are used worldwide. For high-frequency compatibility Rogers use a hydrocarbon ceramic and PTEF (Polytetrafluoroethylene) base in the middle instead of glass fiber. That's why Rogers laminate provides a higher dielectric constant and heat dissipation with the lowest dissipation factor. The Rogers has different series of high-frequency laminates, which can handle signal frequencies of up to +6GHz without any significant signal loss. Some of its widely used series of high-frequency laminates are
Rogers RT Duroid 5880
Rogers RO4000 hydrocarbon ceramic laminates and prepregs
Rogers CuClad® Series Laminates
The application area of Rogers High-frequency laminates include:
Teflon is a brand that uses PTEF (Polytetrafluoroethylene) as the base material to produce high-frequency PCB laminates that fulfill the need for rising speed and frequency. Due to its lower prices than the Rogers PCB laminates, Teflon is the second most used High-frequency PCB substrate. The Teflon laminates transmit signals of +5GHz with exceptional thermal resistance.
Teflon has a wide area of application. They are primarily used in
Panasonic is a PCB substrate and prepregs manufacturer. Megatron 6 is one of its high-frequency PCB substrates that uses hydrocarbon resin as the base material. This material possesses almost the same properties as Rogers. The specialty of Megatron 6 is that, unlike Rogers, this material matches the manufacturing process of FR-4 substrate, so no extra effort is required to get the Megatron 6 PCB manufacturing done, which reliefs the manufacturing cost.
Megatron 6 has a wide application in different areas, such as:
Ceramic printed circuit boards use any one of the three materials, Aluminum Oxide, Aluminum Nitride or Silicon Nitride, as the core/base material, which has many advantages, including compatibility with high-frequency signals, high thermal conductivity and minimum coefficient of thermal expansion (CTE). The dissipation factor (Df) of Ceramic PCB is really low at 0.002, which makes this material perfect for high-frequency devices working in high-humid environments as ceramic PCBs are completely water resistant. Another advantage of Ceramic PCB is that they are lower in cost than Rogers and Teflon.
The material selection for individual boards is different and based on the electrical and environmental conditions of the board. But, some factors may help to conclude a perfect material that matches your requirements.
For a high-frequency circuit, the dissipation factor of a board at 10GHz should range somewhere between 0.002 to 0.0032. Because the dissipation factor of a material determines the signal loss in a circuit, and a lower dissipation factor means slighter signal loss during the transmission. The dissipation factor of each material is not fixed and is determined by different tests. While selecting the material for your project, do check the dissipation factor and the type of test which concluded it to find a suitable material according to the conditions of your board.
The high-frequency boards produce and experience more heat during their life cycle, which raises various issues on manufacturing, assembling and operating levels. As we know, excessive heat drives up the dielectric constant and dissipation factor, which can cause an unexpected signal loss in a circuit. So, in general, the overall goal of finding a suitable high-frequency material concerning heat should be a substrate with a lower coefficient of thermal expansion (CTE), as it can handle heat stress during assembly and operation more diligently than a material with higher CTE. The moisture absorption property of the material also affects the dielectric constant and dissipation factor of the board, especially in high-humidity areas.
The manufacturing requirements of material are one of the major factors that determine the cost of the PCB. As high-frequency PCBs are not a norm, the manufacturers have to take a non-standard way to fabricate them, for which they charge more. When deciding on the high-frequency material, always make sure that it matches the manufacturing process of FR-4. Otherwise, ask your manufacturer what the manufacturing process will be and the price according to that. However, in general, Rogers PTFE-based laminates are compatible with the manufacturing process of FR-4, whereas ceramic-based PCB has a totally different fabricating process.
The specifications state the minimum to maximum details of a high-frequency circuit that are necessary to understand the complexity of the board and select base material. The specifications of a circuit include electrical and environmental factors. As both work together to determine the performance of the PCB.
Laminate is the base material of the PCB, pre-coated with copper on both sides. The signal traces are oriented on each side of the laminate. So, the thickness and material of the laminates are crucial to consider as it determines the shielding between two layers. In an ideal condition, the thickness of the laminate should increase with frequency to provide maximum shielding and reduce crosstalk and EMI issues.
The number of layers and their arrangement depends on the unique requirements of the individual circuit boards. But in the case of high-frequency circuits, each signal layer should have a ground or power plane adjacent to it to maximize the shielding and minimize the volt drop, crosstalk and electromagnetic interference among the signals.
Loss tangent refers to the loss of a signal throughout its transmission. Since high-frequency waves influence the penetration of the signals into the conducting lines, high-frequency circuits experience a high signal loss. To minimize the signal loss in a high-frequency circuit, it is necessary to make sure that the base material has a minimum dissipation factor and dielectric constant.
The material has some unique identification, one of which is its properties. Except in some severe circumstances, the properties of the material never change; for a better understanding of a high-frequency PCB, let's have a look at its properties.
The capabilities of a high-frequency PCB are twice more than the capabilities of a standard FR-4 PCB.
High-frequency PCBs are more robust against thermal resistance. The thermal coefficient of a high-frequency PCB is more than the standard PCB. Hence, high-frequency PCBs are more capable of handling high temperatures without any significant change in signal quality.
A high-frequency PCB has the capability of providing markable performance against humidity. The water absorption property of a high-frequency PCB is negligible.
High-frequency PCBs, especially ceramic PCBs, provide exceptional resistance against chemical erosions. Hence, they have more capability to perform under chemically affected environments such as in chemical laboratories and field areas.
If appropriately stacked up, the electromagnetic compatibility and isolating properties of a high-frequency PCB are always excellent. High-frequency PCBs can provide ideal performance under highly radiated environments. These capabilities of a high-frequency PCB make it superior to use for medical and communication devices, satellites and antennas and power amplifiers.
The frequency of a high-speed PCB ranges from 2 Ghz to 100 Ghz. The PCBs with a frequency of 1-2Ghz can provide ideal output with standard FR-4 material, but high-frequency PCBs require high-frequency laminates to deliver the expected performance.
Until now, Rogers has delivered the best high-frequency laminates with a range of variations that can meet the needs of individual boards. Rogers has a collection of laminates and prepregs divided into multiple series. This series used different base materials for high-frequency laminates, such as ceramic-filled hydrocarbon material with woven glass, Polytetrafluoroethylene (PTEF) and ceramic.
Please keep in mind that there is nothing like “the best material” because a circuit chooses its substrate by itself. Let me elaborate on my point. The material selection of a PCB depends on its specification. For example, if a circuit is operating signals with a frequency range between 2-3 GHz, we can still choose to go with standard FR-4 material, but in this case, we will need a precisely done stack-up and layout. Or otherwise, we can use Teflon PTFE-based laminates instead of Rogers to minimize the budget while keeping the integrity.
NextPCB is one of the experienced manufacturers of high-frequency PCBs around the globe, providing high-quality PCB products with dedicated customer service. We have been manufacturing high-frequency PCBs RF 6-24Ghz, RF 77Ghz and antenna-embedded high-frequency PCBs for a long time. Besides these mentioned PCBs, NextPCB is also ready to meet your custom requirements. At NextPCB, we are willing to help you with your next high-frequency PCB project.
The other services of Next PCB include components sourcing, PCB prototyping/PCB manufacturing, PCB assembly, quality testing, and the final shipment. Briefly, NextPCB can meet all your PCB requirements, from PCB prototyping to small or mass PCB production.
To get a quick online quote within 24 hours, visit the link.
Designing a high-frequency PCB is complex, while following some guidelines always eases the process and provides better opportunities to make the most out of a circuit.
Before starting to dive into the actual designing stuff, you should always make a go-to plan. This plan should include a rough draft of your PCB, the number of sub-circuits you want to have and the number of PCB layers. In most cases planning before starting work aids the speed of the project and eliminates any potential backtracks.
2. Know the Signal Frequency of your PCB and Draft the Stack-up
To know the frequency of a circuit, we need to conclude the voltage and resistance requirements of the components as both influence the frequency. As soon as we have estimated the frequency, it is better to finalize the number of layers and decide the stack-up (arrangement of the layers).
This stage of PCB designing involves the material selection for the PCB. For instance, FR-4 is a standard base material for a normal PCB, but in other cases, such as if a PCB utilizes high-frequency signals or has other specifications; the selection of the PCB substrate for these circuits should take time and meet the requirements of the circuit to achieve the ideal performance.
Along with the process of material selection for the PCB, the designer should also pay attention to the stack-up design of the board, as the arrangements of the PCB layers are somehow a factor in the determination of a board's material.
The ground and power plane ensure the power supply in a circuit and influence its properties. For example, a ground plane kept adjacent to the signal layer provides shielding that prevents cross-talk among high-frequency signals. And if ground and power planes are stacked adjacent, they provide interplane capacitance, which is beneficial for high-speed circuits.
Understanding the ground and power plane and deciding whether to dedicate separate layers for ground and power planes before floor planning can help you achieve more by doing less.
A single PCB has multiple sub-sections. The arrangement of these interconnected sub-sections refers to floor planning. In the initial stage of designing, Floor planning should be the first priority. Floor planning is necessary to follow the size guidelines of the PCB and manage other electrical properties of the circuit. Especially when working with mixed signals, Floor planning is crucial, as it allows placing both analogue and digital sections in a way that they do not create interference and EMI issues.
While designing a high-frequency PCB, minimizing the size of holes and pads will create more space to place other component leads and help to reduce the parasitic capacitance, which occurs due to closely placed conductive elements.
The high-frequency signals are more challenging to route and require several considerations before routing. When routing the high-frequency signals, ensure they are perfectly shielded and not parallel to the signal tracks on their adjacent layers.
For better signal transmission, keep the length of the high-frequency signals short, and if possible route them on a whole different layer adjacent to the ground or power plane (in case there is a layer dedicated to the ground or power plane).
Every independent circuit needs a current return path to prevent the circuit from getting a permanent electric charge. The current return path requires minimum obstruction. While defining the current return paths, place vias wisely. Otherwise, they can cause the current to split on the ground plane. To avoid signal delays when placing the vias, keep the coupling tight.
The closely routed signals, especially high-frequency signals, cause coupling and noise that disturb the rest of the signals. To avoid coupling, the designers use a basic rule called the 3W rule, which states that the gap between two signal traces, when measured from the center of trace one to the center of trace two, should equal the thrice width of the signal trace.
If the PCB is operating extremely high-frequency signals, the designers can increase the distance between the traces from 3 times to as many times as they consider necessary.
Closely placed power and ground planes possess a risk of coupling. The coupling between the adjacent planes is more critical than the signal coupling, as in this case, the ground starts absorbing fringing instead of radiating it out.
In a high-frequency PCB, the designers can tackle plane coupling by following the 20H rule. The 20H rule emphasizes that the thickness of dielectric material between adjacent power and ground plane should be 20 times the thickness of the power plane.
Once you have taken all the above stated measures into the account, it's time to kick start the layout designing. But, be mindful of general PCB routing tips and guidelines to ensure maximum electrical properties and ideal output.
The fabrication process of high-frequency PCBs involves several steps. Each of these steps is crucial to getting the ideal output from the PCB. The process remains the same for all kinds of PCBs but what actually changes is the curing temperature, pressure, the amount of electroplated material and the time of pressure washing. These changes totally depend on the requirements of the individual boards. For example, the boards with thicker copper layers require more time to dissolve the copper in the etching process and also require more time in the process of electroplating to deposit the required amount of conducting material on the walls of drilled holes.
Maybe this information is a little bit more before having a good knowledge of the PCB fabrication process. But no worries, here we have explained the high-frequency PCB fabrication process in-depth.
The stack-up of a board is the first condition that makes sure the ideal performance of the printed circuit boards. The process of stack-up design involves the arrangement of the board layers according to the requirements of the PCB. As soon as the stack-up is finalized the process of layout design starts. The layout design of a PCB involves the routing of the signal tracks through software. After finishing the Blueprint of your PCB, deliver it to your PCB manufacturer to start the fabrication process, which involves several steps.
Layout printing is the step of converting digital layers into solid films through a plotter printer; these films can be considered the negatives of the PCB layers.
To print the blueprints plotter uses two types of inks, black and transparent. The black ink prints the conducting traces of the PCB, while the transparent ink prints the non-conducting areas. Whereas on the outer parts of the PCB, the function of the inks changed, the black ink indicates the non-conducting area, and the transparent ink represents the conducting part of the layer. This inverse function of inks will later help to etch the excess copper from the laminates.
Each layer of the PCB requires a unique blueprint layer. After printing the layers, these layers go through a process of punching holes into them to make them align with other layers of the PCB in the process ahead.
The preparation of inner copper layers is the process of converting blueprints on the copper-clad laminates. This process of printing inner layers starts with cleaning laminates to wipe off any dust, which can later cause shorts and open circuits. The laminates are the cores of the PCB, as in the case of high-frequency PCBs, any high-frequency material (Rogers, Teflon, and Ceramic) pre-coated with copper on both sides.
After cleaning the laminates, the manufacturer applies a coat of photosensitive material called “photoresist” on the laminates. Then, on the surface of the UV printer, the laminates are aligned through the punching holes with the blueprints in a manner that the laminate is sandwiched between the blueprints of the PCB. The UV light hardens the transparent area and leaves the dark area unhardened.
The next step is to wash the laminates with a strongly alkaline material to remove the unhardened photoresist.
The etching means the removal of exposed copper. The process of dissolving and removing the exposed copper is a slow, pressure-washed process done with an alkaline solution. This process only leaves the traces of copper that were hardened in the previous step and completely vanished from all the exposed area (unhardened photoresist area from which the photoresist material was removed in the previous step).
As soon as all the inner cores are ready, an automated punching machine drills the registration holes into the cores later; these registration holes help align the inner and outer PCB layers. Further, an Automatic Optical Inspection (AOI) machine cross-checks the cores against the original layout files to find errors in the cores. If there is no error in the laminate, the process stays continued.
In the binding process of the PCB, for example, consider a 4-layer PCB. On a plate of steel, the different layers are stacked as Copper foil/Prepreg(s)/Core/ Prepreg(s)/Copper foil. Then the steel base has another top steel plate which is placed and pressed. After this, the stack is put under a high temperature to melt the Prepreg, which binds the cores and copper foils together to make a firm structured PCB.
However, the alignment of the layers is the most crucial part of this whole process, as a tiny mistake can later ruin the whole PCB in the drilling process. That is why in the previous process, registration holes were drilled to keep all these layers aligned.
The manufacturer X-rayed the PCB to mark the hidden holes and vias before drilling. This is an automatic process to avoid errors.
In this step, the PCB stack is put into the big tanks for electroplating, which is the process of depositing conducting material to the walls of drilled holes and vias.
The preparation of outer layers repeats the same process as the preparation of inner layers.
After finalizing the outer layers, the manufacturer applies a coat of solder mask, a liquid epoxy, and cures it in the ovens to make it stick to the surface. The solder mask prevents the oxidation of outermost copper tracks and shorts on the outer layers.
Silk screening is a process of printing information regarding components and brands on the Outermost layers of the PCB.
Testing the PCB after its completion is the most important step. The testing of the PCB mainly involves two types of testing continuity and the isolation levels of the PCB layer as it makes sure that there are no shorts in the circuit. This process is mostly automatic.
After all this, the PCB is cut into the required size and delivered to the customers.
Due to its robust nature against high temperatures and compatibility with high-speed technology, high-frequency PCBs have a wide range of applications in different industries. They include
Medical devices that use high-frequency signals and radiations such as X-rays, Gamma-rays and ultrasonic waves create an electromagnetic environment in their surroundings. As we know, high-frequency PCBs provide electromagnetic compatibility; these PCBs have a number of applications in these medical devices.
Military devices usually operate under rough environmental conditions and are highly sensitive to minor errors. The mechanical properties and minimal loss tangent of a high-frequency PCB makes it more reliable to use for sensitive devices such as firearms, missiles and aircraft.
With the revolution of technology, the industry is civilizing and changing expeditiously. This revolution is driving the demand for faster machinery with more accuracy and increased operational time. As per the scenario and rising demand for reliability and performance, high-frequency PCBs are replacing standard PCBs due to their limitations. These days high-frequency PCBs have vast applications in measuring equipment, heavy machinery, power indicators and electromechanical devices.
The communication systems are under high electromagnetic waves and cause electromagnetic interference among signals. Further, on these devices, the frequency is super high, which can cause crosstalk if not appropriately treated. In this field, the transmission and receiving devices are usually placed at a distance and communicate through frequencies. Thus, even a minor signal loss is not tolerable. To transmit signals without a significant loss on larger distances, the signal requires amplification and minimum loss tangent. Due to the precise requirements of this field, there is a non-other option than a high-frequency PCB. The power amplifiers and other communication devices, such as satellites, and radio transmitters, utilize high-frequency PCBs on a big scale.
The difference between a high-speed and high-frequency PCB relies on the basic concept of time. A high-speed PCB transmits data at a very fast rate, whereas a high-frequency PCB ensures shorter circuit cycles.
In-depth, a high-speed PCB allows the transmission of a large amount of data through analogue or digital channels. On the other hand, a high-frequency PCBincorporates some special features that reduce the signal loss during transmission.
But the debate on the difference between high-speed and high-frequency PCB does not stop here. Because there is not a reliable difference between them (at least in terms of electrical properties and material) it is hard to prove them different or alike.
Here we are discussing some basic information about the high-speed and high-frequency PCBs so that you can have a better understanding of both.
By this time, I hope you have understood that there is no factual difference between both and when you will have to design a high-speed or high-frequency PCB, instead of being stressed about the material and its properties, you will work hard on routing signals appropriately to achieve your ideal performance.
The features of a product describe its main characteristics. Understanding the features of high-frequency PCBs may aid your knowledge about high-frequency PCBs and will help you to choose between the two.
The NextPCB manufactures three main types of high-frequency PCBs. They include
RF 6-24Ghz PCBs can handle signals of the frequency range between 6-24Ghz without significant signal loss. These are the most commonly used high-frequency PCBs and are capable of making a stable connection within the limit of 30 meters.
An extremely high-frequency board, with a wavelength of two third of RF 6-24Ghz PCBs,
and a higher range of detection areas.
Antenna-Embedded PCBs is a modified type of high-frequency PCBs, particularly used for communication devices. These PCBs have small conductor width, conductor spacing and conductor tolerances. Antenna-Embedded PCBs possess round corners, higher and improved radio frequency performance and reduced power consumption.
To get a quote on any of these PCBs, contact us.
If compared to the standard PCB, the advantages of a high-frequency PCB are numerous.
A high-frequency PCB operates at a frequency of more than 2Ghz. The role of high-frequency PCBs in the rapidly changing world of technology is vital to meet the demands of higher temperature resistance and faster transmission rate.
A good selection of materials and considering some important designing aspects of PCB while designing the PCB can help you achieve lower signal loss and prevent crosstalk and EMI issues.
Understanding the properties, features and capabilities of a high-frequency PCB can help you determine the type of high-frequency PCB you need for your project, which may help you cut down your budget.
The high-frequency PCBs have a wide application in mainstream areas and industries. Due to their reliability and exceptional performance against harsh environmental conditions, they have wide application in aircraft, missiles, firearms, medical instruments, communication systems, power amplifiers and so on.
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