High frequency PCBs are one of the widely used boards in the engineering world. These PCBs are known for their wide range of features and properties. PCBs are an integral aspect in the production of any electronics.
The use of a high frequency PCB can’t be underestimated. This circuit board has been used for the production of various electronics. In this article, we will be discussing important things you need to know about this PCB.
High Frequency PCB – What is it?
High frequency printed circuit boards transmit electromagnetic waves with minimal losses. This type of PCB is commonly utilized in applications where transmission of signals between objects is required. In the fabrication of a high frequency PCB, the use of specific materials is required.
This board features faster rates of signal flow. Its frequency range is about 100 GHZ. High frequency boards offer low levels of thermal expansion, lower DF, and lower DK. These circuit boards are commonly used for HDI technology.
Properties of High Frequency PCB
High frequency PCBs offer a wide range of properties. Understanding these properties helps you to understand these PCBs. These printed circuit boards are called high frequency PCBs because of the properties they offer. Let us have a look at the properties of these PCBs.
Dissipation factor: HF PCBs have a low dissipation factor which falls between 0.0019 and 0.025. This value helps to ensure that the signal transmission rate isn’t affected. Low dissipation factor also enables improved signal transmission. A lower dissipation factor can help to minimize signal loss.
Low and stable dielectric constant: The dielectric constant of a high frequency PCBs is lower and stable. This helps to ensure frequency transmission. This also ensures less signal delay. Lower dielectric constant leads to higher rate of frequency transmission.
Chemical resistance: High frequency PCBs can withstand chemicals. These boards can survive chemical attack when exposed to one. Due to this property, these circuit boards are less likely to corrode.
Low moisture absorption: These PCBs have a low rate of water absorption. It doesn’t absorb moisture and as such, it can withstand a humid environment.
Low dimensional stability: High frequency PCBs feature low dimensional stability. These PCBs maintain their size irrespective of the temperature they are exposed to. Even when they are exposed to heat, their size remains the same.
Guidelines for Designing High Frequency PCBs
PCB designers need to take some steps when designing high frequency PCB material. Below are steps that need to be taken;
Plan your design: Before you commence with the PCB design, it is vital you have a design in mind. Doing this will help you to prevent anything that might cause setbacks for your design. Having a checklist is an important way to go about this.
Determine the PCB signal frequency: Make sure you determine the voltage and power demands for the integrated circuits. Decide if you will be dividing any power planes. You also need to check if different signals can be accommodated. The manufacturer helps to ensure what the requirements for minimal tolerance are. It is important you have a plan of how to reduce the noise level on your high-frequency signals.
Draw up board stack up plan for production: Immediately you plan how to design the PCB, it is important to write down the demands for the stack up layer. You can seek the help of the manufacturer to know the specific material for your PCBs. It is important you understand the specific constraints and materials for your circuit board.
Plan the floor: When it comes to floor planning, you have to divide your PCB into sections. You need to determine if you will be placing your subcircuits into a bigger design. This is important when there are digital and analog sections that need to be carefully isolated to reduce interference.
Determine the power and ground planes: This is an important step. After you have defined the PCB layout, you need to examine your design. You need to understand the ground plane. You may not have to divide the ground plane using a routed signal.
Dividing the ground plane indicates that you need to rotate the void. This may influence the signal timings and EMI. Dividing the ground plane is necessary. Make sure a resistor is included along the signal trace. This will help the signal have a gap which enhances the return path.
Reduce the size of land patterns: High frequency PCBs often feature small pad. Their pads are smaller than that of other PCBs. Reducing the PCB space helps to ensure the PCB is useful. You can also maintain the pad size to match the component pins size.
Reducing space comes with several benefits. This will minimize the parasitic capacitance and increase the mechanical strength. If you reduce the space, there will be more space for various pairs.
Route the frequency signals: If you want to get more shielding benefits of this board, you need to route your frequency signals. High-frequency signals produce high radiation. There can be interference between two separate signals due to this. Routing the frequency signals can help you prevent this from happening.
Design a good current return path: For high frequency PCB, every signal needs a route. The route begins from the source ending at the sink via the path. Minimal obstruction is required by the path. This is an integral part of the design and fabrication of high frequency substrates.
In some cases, you might need to utilize a via to make sure the path remains smooth. The currents will likely spread over divisions on your ground plane if you don’t do this.
Use 3W rule to reduce trace coupling: When it comes to signal integrity during transmission, line coupling may result in a serious challenge. The 3W rule will help you to reduce this. Applying this rule will ensure there is increase in the distance between the traces and as such, minimizing the coupling effect.
Apply 20H rule to reduce plane coupling: When there is coupling between ground and power planes it can be a threat to your PCB design. According to the 20H rule, you need to make sure the thickness between the adjacent power and ground plane is much thicker than the power plane.
Fabrication Process for High Frequency PCBs
The fabrication process of high-frequency circuit boards is a straightforward one. It is very easy to fabricate a PCB if you can understand some considerations.
Make a PCB design: This is the first thing you do. Here, you have to plan where the PCB blueprint will be placed. You can utilize Extended Gerber, designer software, to help with your design.
Print PCB design: Here, you print your PCB design. A plotter printer is used for printing. This printer produces a PCB film. This film has two ink types, the black ink and the clear ink. The clear ink shows the non-conductive areas of the PCB. The copper and the circuit of the board use the black ink.
Print copper for the inner layers: In this stage, the PCB manufacturing starts here. After printing the PCB on the laminate, the copper will be pre-bonded on the exact laminate that serves as the PCB structure. To unveil the initial PCB blueprint, the copper can be engraved.
Layers alignment: In high frequency PCB manufacturing, the layers have to be aligned. The holes can be used to arrange both the outer and inner PCB layers.
PCB layers lamination: Here, you laminate the PCB and the lay-up steps. Prepare the outer and inner layer and then join them. A metal clamp can help you join the layers.
Plating of PCB: For PCB plating, you will need chemicals. These chemicals will help you sandwich the layers together. Ensure you clean the board before using different chemicals on it.
Solder masking: Here, the panel has to be cleaned before applying the solder mask. An epoxy ink and the solder film will be applied.
Screening and finishing of silk: The PCB will be either plated with HASL, silver, or gold. This will provide shielding to the copper and the pad. Silk screen the PCB after it has been plated.
Testing: To ensure your circuit board functions well, you are required to test it. The isolation and circuit continuity tests are an example of these tests.
High Frequency PCB Applications
High frequency PCBs are used in various applications. These boards are specially fabricated to meet the requirements of high temperature applications. They are used in applications like;
Advanced communication system: These boards are used in the communication systems. They are commonly used in filtering devices, amplifiers, booster stations, and receivers.
Military industry: High frequency PCB materials are used in the production of ammunition and firearms.
Radar systems: These PCBs play a vital role especially in the marine and aviation industries. Radar systems prevent ships from obstacles like icebergs in marine application. The radar system guides aircraft and as such prevents accidents.
Medical systems: These boards are used in the manufacturing of medical electronics like monitoring and diagnostic devices.
High frequency PCBs offer great features that make them suitable for use in different applications. They meet the demands of high-frequency and high-performance applications. These boards are popular in the electronics industry.