High frequency PCBs are used in embedded systems. These PCBs enable the transmission of high frequency (GHz) electromagnetic waves. These PCBs are complex in design and require high integrations and high layer density. Owing to such complexities involved, the design and fabrication of these PCBs require several critical considerations. This post discusses different layout tips that would lead to effective high frequency PCB design.
Challenges Associated with High Frequency PCB Designs
The common challenges associated with the design and fabrication of high frequency PCBs are listed below.
- Component placement for isolation between the analog and digital sections of PCBs
- High impedance
- Maintaining power integrity across all layers
- Complex wiring through multi-level stack up
All the above-mentioned challenges are commonly faced by PCB designers while designing a high frequency PCB. The next section offers few proven layout tips that will help reduce the complexity of high frequency PCB design.
Layout Tips to Make High Frequency PCB Design
The following techniques can enhance the design and fabrication process of high frequency PCBs.
Material Selection: Material selection is a crucial factor, as different materials possess react differently to electromagnetic frequencies. High frequency PCBs require robust construction and good dielectric properties. The following are a few common materials used for making these PCBs.
- Taconic TLX
- Rogers 4350B HF
- Rogers RO3001
- Rogers RO3003
- ISOLA IS620 E-fiber glass
- ARLON 85N
Multi-Layer Stacking: Multi-layer design supports the integration of high density wiring. The strategic stack-up of PCB layers can enhance the frequency of transmission. The multi-layer design contributes to design efficiency in the following aspects.
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Multi-layer stack up assures uniform distribution of components, and wiring to reduce the complexity on each layer.
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It reduces the interference.
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It offers better heat dissipation.
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It generates lower noise and vibrations due to uniformly placed components.
Reduce Number of Alternating Leads: Having a fewer number of alternating leads can enhance the frequency. Each alternating lead adds on one via. Each via offers 0.5pF of distribution capacitance. Therefore, reducing the number of leads can result in a reduction of capacitance and enhanced frequency tolerance.
Shorten the Lead Length: The lead length between the PCB pin and high-frequency circuit must be short. This is recommended due to the directly proportional relationship between the routing distance and radiation intensity. The longer the routing length higher will be the radiation intensity and therefore the electromagnetic frequency transmission may reduce. Also, if routing wires are kept straight, better efficiency can be achieved.
Prevent Crosstalk Between Parallel Leads: Crosstalk between the parallel leads on a PCB can reduce the frequency tolerance. Crosstalk is the action of coupling or signal interference without direct contact between the two leads of PCB. The distance between two parallel leads must be kept maintained to certain recommended inches to prevent crosstalk in high frequency PCBs.
Route the PCB with Section Isolation: High frequency PCBs consist of two sections, namely, an analog ground line and a digital ground line. The interference of electromagnetic signals between these two sections can damage the high frequency PCBs. That is why during the design and fabrication, both sections should be isolated. Also, if interconnection between both sections is required, then a high frequency choke magnetic connection link can be established.
Prevent Lead Looping: Loops formed during establishing circuit connections can result in short circuits or the generation of heated zones. Therefore, lead looping should be prevented. If it cannot be prevented, the loop area should be made as small as possible.
High frequency PCBs can be designed and fabricated effectively by following the above-mentioned tips. However, it is important to acknowledge that the design and manufacturing of such PCBs require expertise, therefore, these fabrication services should be sourced from reliable manufacturers like Accelerated Assemblies. The company offers high quality customized PCB fabrication services. Their high frequency PCBs are assured for quality as they are certified with Quality Assurance Systems (QAS) International.
