Designing of High Frequency PCB
While designing high frequency PCB material, PCB designers need to follow some guidelines. The steps that are need to be taken are mentioned below :
Planning of your Design:
It is very important to have a design in your mind before you begin with the PCB design. This step will help you to prevent anything that might cause setbacks for your design. The best way to go about this is to have a checklist.
Calculate the PCB signal frequency
In this step, you need to determine the voltage and power required for the integrated circuits. Decide whether you will be dividing any power planes. You also need to check if different signals can be accommodated. The manufacturer helps to ensure the requirements for minimal tolerance.
Draw up board stack up plan for production
As soon as you plan the design of the PCB, it is important to write down the demands for the stack up layer. You can ask the manufacturer to know the specific material for your PCBs. It is important that you understand the specific constraints and materials for your printed circuit board.
In floor planning, the PCB is divided 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
After defining the PCB layout, it is important to examine the design. For this 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, which may influence the signal timings and EMI. It is necessary to divide the ground plane. Make sure a resistor is included along the signal trace as this will help the signal have a gap which enhances the return path.
Reducing the size of land patterns
High frequency PCBs often feature small pad (smaller than that of other PCBs). Reducing the PCB space helps to ensure the usefulness of the PCB. You can also maintain the pad size to match the component pins size. Reducing space comes with several advantages such as, minimizing the parasitic capacitance and increase the mechanical strength. Reducing the space, gives more space for various pairs.
Route the frequency signals
High-frequency signals produce high radiation. Hence, there can be interference between two separate signals. Hence, it is important to route the frequency signals. Routing the frequency signals help you prevent this.
Design a good current return path: For high frequency PCB, every signal needs a route which begins from the source and ends at the sink via the path. There should be minimal obstruction in the path. This is an integral part of the design and fabrication of radio frequency substrates.
In some cases, via is utilized to make sure that the path remains smooth. If you don’t do this, the currents will likely to spread over divisions on your ground plane.
Using 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 have to make sure that the thickness between the adjacent power and ground plane is much thicker than the power plane.
Fabrication of High Frequency PCBs
The fabrication process of high-frequency PCBs is quite easy . For this you need to follow some considerations :
1. Make a PCB design: Before going for the fabrication you need to plan where the PCB blueprint will be placed. You can use Extended Gerber, designer software, to help with your design.
2. Print PCB design: In the second step, you need to print your PCB design using a plotter printer. 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.
3. 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.
4. 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.
5. PCB layers lamination: In this steps the PCB is laminated. The outer and inner layer are prepared and then joined. A metal clamp is used to join the layers.
6. Drilling: Here, An X-ray machine is used to determine the drilling spots. Then holes are drilled to secure the circuit board. The extra copper can be filed off after completing the drilling.
7. Plating of PCB: For PCB plating, chemicals are used. These chemicals help you sandwich the layers together. You have to ensure that your board is clean before using different chemicals on it.
8. Solder masking: Here, the panel needs to be cleaned before applying the solder mask. An epoxy ink and the solder film are then applied.
9. Screening and finishing of silk: The PCB will be either plated with HASL, silver, or gold to provide shielding to the copper and the pad. Silk screen the PCB after it has been plated.
10. Testing: To ensure the functionality of the PCB, you need to test it. Example : The isolation test, circuit continuity test.
11. Cutting: Once you have tested your PCB, you can make some cuts from your PCB panel. The PCB cutting can be done through a CNC machine or a V-a groove.
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