Introduction
The deployment of 5G networks is rapidly accelerating globally, with the new technology promising faster data speeds, lower latency, and the ability to connect massive numbers of devices. A key component that enables the functioning of 5G networks is the 5G printed circuit board (PCB). 5G PCBs facilitate the transmission of 5G signals and help achieve the high frequencies needed for 5G.
However, designing 5G PCBs comes with unique challenges compared to previous generations of wireless technology due to the higher frequencies used. New PCB materials and careful design considerations are required to account for signal loss, impedance control, thermal management, and more.
This comprehensive guide will provide electronics hardware designers and engineers with an overview of key considerations and best practices for designing 5G PCBs. Topics covered include:
- 5G frequency bands and data rate requirements
- Selection of PCB materials and properties to consider
- Layout techniques for improved signal integrity
- Strategies for thermal management
- EMI and signal loss mitigation techniques
- Testing and validation methods
By the end of this guide, you will have a solid understanding of how to design and optimize 5G PCBs to fully take advantage of 5G capabilities.
5G Frequency Bands and Data Rates
The frequencies used for 5G networks are a major difference compared to previous generations of wireless technology. 5G uses frequency bands in the high-frequency millimeter wave (mmWave) ranges between 24 GHz to 52 GHz, as well as some sub-6 GHz frequencies.
The advantage of mmWave frequencies is the availability of large amounts of contiguous spectrum which enables very high data rates. The mmWave bands currently defined for 5G use include:
- n257 (28 GHz)
- n258 (26 GHz)
- n261 (27.5 GHz – 28.35 GHz)
Some of the key 5G frequency bands and corresponding data rates include:
| Frequency Band | Data Rate |
|---|---|
| 600 MHz | 100 Mbps |
| 2.5 GHz | 1 Gbps |
| 4.7 GHz | 1.3 Gbps |
| 24 GHz | 3 Gbps |
| 28 GHz | 5 Gbps |
| 39 GHz | 7 Gbps |
However, the higher frequency mmWave signals also have much shorter wavelength and cannot penetrate obstacles as well. This leads to higher path loss and requires more advanced antenna technologies like massive MIMO and beamforming.
When designing a 5G PCB, the frequency bands and data rate requirements need to be carefully considered to ensure the board can support high frequency signals with adequate gain and minimal loss.
PCB Substrate Materials for 5G
The selection of the appropriate PCB substrate material is critical for 5G design. The dielectric substrate material separates copper layers in the PCB and impacts loss tangent, dielectric constant, thermal conductivity and other properties. Some key considerations for 5G PCB substrate selection include:
Dielectric Constant
A low dielectric constant (Dk) helps reduce signal loss and cross talk. Common low Dk substrates for 5G PCBs include fluoropolymers like PTFE (Dk of 2.1) and liquid crystal polymers (LCP) with Dk between 2.9-3.3.
Loss Tangent
The loss tangent indicates the material’s inherent signal loss due to dielectric absorption. Lower loss tangent values below 0.005 are desirable for mmWave 5G boards. Rogers RO3000 series laminates have loss tangents between 0.0021-0.0027.
Thermal Conductivity
The high power density of mmWave circuits leads to substantial heat generation. Using thermally conductive substrates like ceramic aluminum nitride (170 W/mK) and liquid crystal polymer (0.67 W/mK) helps dissipate heat.
Coefficient of Thermal Expansion (CTE)
Matching CTE between PCB and components prevents solder joint failure and pad cratering during thermal cycling. Glass reinforced hydrocarbon laminates offer CTE compatibility with common components.
Moisture Absorption
Materials like PTFE have very low moisture absorption, helping maintain stable electrical performance. High moisture absorption of substrates should be avoided.
Thickness
Thinner dielectrics help reduce loss at mmWave frequencies. While thickness depends on layer count, substrates between 0.1mm to 0.3mm thickness are typical for 5G.
Here is a comparison between some popular 5G PCB substrate materials and their properties:
| Material | Dk | Loss Tangent | Thermal Conductivity | CTE | Moisture Absorption |
|---|---|---|---|---|---|
| Rogers RO3003 | 3.0 | 0.0013 | 0.31 W/mK | 17 ppm/°C | 0.06% |
| Rogers RO4835 | 3.33 | 0.0031 | 0.74 W/mK | 11 ppm/°C | 0.04% |
| Taconic RF-35A2 | 3.5 | 0.0018 | 0.69 W/mK | 7 ppm/°C | 0.02% |
| Polyimide | 3.4-3.6 | 0.002-0.004 | 0.12 W/mK | 20-70 ppm/°C | 1-4% |
| PTFE | 2.1 | 0.0002 | 0.25 W/mK | 17 ppm/°C | 0% |
| LCP | 2.9 | 0.0025 | 0.67 W/mK | 17 ppm/°C | 0.04% |
| Aluminum Nitride | 8.9 | 0.0001 | 170 W/mK | 4.3 ppm/°C | 0% |
Layer Stackup Design
The layer stackup defines the number of copper and dielectric layers in a PCB. An optimal stackup is important for controlling impedance, minimizing loss and ensuring signal integrity at 5G frequencies. Here are some key guidelines for 5G PCB stackups:
- Use thicker copper layers (2oz/ft2 or more) to reduce conductive losses
- Minimize number of lamination cycles to limit signal loss
- Include ground planes close to signal layers for impedance control
- Keep layer count low, typically 4-8 layers for optimum 5G performance
- Use symmetric stripline configurations for differential pairs
- Manage layer transitions carefully using tapers/chamfers
- Adopt a split power plane approach to isolate noise-sensitive supplies
- Allow for thermal vias beneath hot components to dissipate heat
A sample 8 layer stackup for a high frequency 5G board could be:
| Layer | Function | Thickness |
|---|---|---|
| 1 | Signal | 2 oz Cu |
| 2 | Ground | 1 oz Cu |
| 3 | Power | 2 oz Cu |
| 4 | Signal | 2 oz Cu |
| 5 | Ground | 1 oz Cu |
| 6 | Power | 2 oz Cu |
| 7 | Ground | 1 oz Cu |
| 8 | Signal | 2 oz Cu |
The close proximity ground planes help control impedance, reduce EMI, and minimize crosstalk. The split power planes isolate digital and analog supplies. Thicker 2oz copper minimizes conduction losses.
5G PCB Layout Guidelines
Careful attention must be paid to the PCB layout to achieve design objectives for 5G performance, signal integrity and EMI control. Some key 5G layout techniques include:
Maintain 100 Ohm differential impedance for interface traces by tuning trace width/spacing based on stackup. Minimize length differences between differential pairs.
Isolation Between RF and Digital
Separate RF and digital sections on layout using ground/shielding barriers. Prevent noise coupling by distance and orientation.
Minimize Trace Lengths
Keep trace lengths as short as possible on mmWave nets to reduce insertion loss. Use surface mount devices for shorter connections.
EMI Shielding
Incorporate shielding cans, guard traces, and ground/power moats to contain EMI emissions. Prevent slot antennas from forming.
Power Delivery Network
Use enough decoupling capacitors close to IC pins, and lower impedance power distribution for clean, stable supply rails.
Thermal Management
Allocate space under hot devices for thermal vias/metal slugs to conduct heat. Use internal cutouts/keepout zones for airflow.
Antenna Integration
Properly integrate antenna arrays within board or align edge mounts using cutouts and milling. Match impedance.
Test Points
Include test/probe points to validate performance over frequency, such as with network analyzers and TDR measurements.
With careful implementation of these guidelines, the PCB layout can be optimized for superior 5G signal integrity.
Mitigating Loss and Signal Integrity
Maintaining signal integrity and minimizing loss is critical for 5G PCBs due to the higher frequencies involved versus 4G or Wi-Fi. Some techniques to help mitigate loss and improve signal performance include:
Extensive Ground Stitches
Connecting all ground planes and areas with many via and microvia stitches reduces ground inductance.
Backdrilling (Via Stub Removal)
Backdrilling unused portions of plated through holes improves impedance matching and reduces reflections.
Buried/Blind Vias
Using vias that span only 2-3 layers controls coupling compared to full-depth drilled vias.
Smooth Layer Transitions
Tapered chamfers/rounded corner pads on layer transitions prevent abrupt impedance discontinuities.
Spacing from Ground
Maintaining adequate clearance from ground layers prevents energy loss through substrate radiation.
Matched Length Routing
Tuning trace lengths to match electrical lengths improves insertion loss in differential pairs.
Periodic Voiding
Introducing voids along a reference plane reduces eddy current losses at high frequencies.
Dielectric Coatings
Applying low-loss tangent coatings (e.g. paralene, PTFE) on traces cuts down on surface wave propagation loss.
With careful modeling and simulation, these techniques can be implemented to fine-tune 5G board performance.
Thermal Management Approaches
Thermal management is a significant concern for 5G PCBs due to increased power densities at mmWave frequencies. Here are some approaches to effectively dissipate heat:
- Metal core substrates – Base laminate itself is aluminum or copper for spreading heat
- Thermal vias – Drilled holes filled with metallization conduct heat to inner layers
- Heatsinks/heat-spreaders – Use machined aluminum heatsinks with thermal interface material
- Fans/air flow – Incorporate small fans or ventilation channels into enclosure
- Phase change materials – Substrates with materials that undergo phase change to absorb heat
- Vapor chambers – Hollow chamber with working fluid that evaporates and condenses, transferring heat
Ideally, thermal management techniques should be modeled during design to predict temperature gradients and optimize heat flow.
EMI Control Methods
EMI control is necessary in 5G designs to prevent interference with other devices and ensure conformance to EMI/EMC standards. Methods to control EMI include:
- Metal shielding cans over sensitive ICs
- Small aperture waveguide vents on enclosures
- Ground plane stitching through multiple layers -strategic placement of ground vias forming “walls”
- Filtering components like ferrite beads on I/O
- Additional shielding gaskets on enclosure seams
- Internal metal compartmentalization to prevent slot antennas
- Careful component placement to contain noise sources
- Sparse power plane fills with islands disconnected at DC
Prototyping and testing needs to validate EMI performance. It may be an iterative process as issues are found and fixes incorporated. Shielding, filtering and isolation are key principles to follow for managing EMI and EMC.
Testing and Validation
Throughout the PCB development process, testing and validation should be conducted using the following methods:
Simulation and Modeling
Perform 3D EM simulations of traces, stackup, PDN, thermal performance. Identify problem areas through modeling.
Frequency Sweeps
Use a network analyzer for insertion loss, return loss, and impedance measurements over frequency. Verify input to output magnitude and phase.
VSWR and Losses
Evaluate voltage standing wave ratio (VSWR), gain, and losses. Look for impedance discontinuities and unexpected resonances.
Eye Diagrams
Eye diagrams show signal integrity and jitter. A widely open clear eye is desired for clean signaling.
Time Domain Reflectometry
TDR plots will reveal impedance mismatches and discontinuities along a trace from reflections. Useful for controlled impedance validation.
Vibration/Shock
Assess mechanical robustness under vibration and shock conditions. Check for solder joint cracks or trace/via fractures.
Thermal Imaging
Use an IR thermal imaging camera to map board hot spots and temperature gradients. Identify cooling deficiencies.
EMI Diagnostics
Test for radiated and conducted EMI compliance. Sniff out specific noise sources.
With careful testing and validation, potential issues can be caught early and addressed to ensure optimal 5G board performance.
Conclusion
Designing printed circuit boards for 5G applications presents new challenges compared to previous wireless generations due to the use of mmWave frequencies and higher data rates. However, through careful planning and optimization across PCB materials selection, stackup design, layout considerations, thermal management, and EMI strategies, a high performance 5G board can be realized.
By following the guidelines and techniques outlined in this article, PCB designers can fully unlock the capabilities of 5G technology and facilitate the rollout of faster, lower latency 5G networks. With attention to signal integrity, thermal management and EMI control, the next generation of wireless connectivity can be achieved through optimal 5G PCB implementations.
Frequently Asked Questions
Q: What are some key differences between designing PCBs for 5G vs 4G?
A: Some key differences include:
- 5G uses higher mmWave frequencies between 24-52 GHz requiring attention to loss, impedance control and thermal issues. 4G uses lower frequency bands.
- Shorter mmWave signal wavelengths require smaller PCB features and tighter layout tolerances.
- 5G PCB materials favor low-loss, thermally conductive substrates whereas FR-4 was common for 4G.
- Beamforming antennas and higher power density ICs lead to greater thermal challenges.
- Shorter mmWave signal paths, isolation and EMI control are more critical in 5G design.
Q: How can signal loss issues be identified in 5G PCB design?
A: Methods to identify signal loss issues include:
- Performing insertion loss simulations on critical high speed nets
- Using TDR analysis to find impedance discontinuities causing reflections
- Evaluating S-parameter results from VNA tests for excessive loss at 5G frequencies
- Analyzing eye diagrams for signs of signal degradation from loss or distortion
- Measuring channel operating margin and link budgets to model expected vs actual loss
- Thermal imaging to check for excessive heating of traces causing resistive losses
Q: What are some methods to control EMI for 5G boards?
A: Techniques to control EMI in 5G PCB design include:
- Use of shielding enclosures and cans to contain emissions
- Careful component placement and orientation to avoid noise coupling
- Extensive ground plane stitching to reduce ground loop antennas
- Strategic use of ground/power moats around circuits
- Filter components like ferrites beads to suppress noise
- Limiting slot/aperture openings in enclosures
- Sparse fills and islands on power planes to reduce coupling
- Tight board-to-chassis grounding to shunt EMI away
- Prototyping and testing to identify issues and refine design
Q: How can signal integrity be maintained for sensitive 5G links?
A: Some best practices for maintaining signal integrity include:
- Matched length differential pairs to control skew and dispersion
- Cross-talk mitigation through distance and routing orientation
- Choosing low loss PCB materials and laminates
- Adding low loss coatings on traces when needed
- Proper backdrilling of unused via sections
- Careful design of transitions between layer changes
- Simulation and characterization of channel frequency response
- Managing noise through isolation and filtering
- Minimizing trace lengths whenever possible
Q: What kind of validation testing should be done on 5G PCB prototypes?
A: Recommended validation tests include:
- Frequency domain measurements using VNAs to characterize insertion loss, return loss, VSWR
- Time domain analysis with TDR to find impedance discontinuities
- Signal integrity checks using eye diagrams, jitter analysis
- EMI testing for radiated and conducted emissions
- Vibration and shock testing for mechanical integrity
- Thermal imaging and measurement of temperature gradients
- Functional testing to verify performance under use conditions
- Correlation to simulation models and results
5G PCB Technology – A Revolution in Telecommunication Industry
High Profile 5G 12 Layer PCB developed At Rayming PCB
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5G technology
5G Pcb Board
The 5G (stands for 5th Generation) technology is the whole new innovation in the field of telecommunication industry. It is the iteration of existing cellular 4G LTE (Long Term Evolution) technology. This 5G technology can break the records of high speed and reliable internet connection, cellular and satellite communication. It is estimated that average download speed of up-to 1GBps and the data rates as high as 20 GBps with latency less than 1mS is possible. This is astonishingly amazing to know that this high speed communication can open new doors to various applications in small
and large businesses, entertainment and multimedia, smart home, autonomous driving in automobile sector, Medical field in surgery, technology, mobile, and satellite communication and in IoT.
Latency: It is the time required by data to travel from source to destination.
The high speed 5G technology can enable the real time control and monitoring of machines and devices like robots, drones, automobiles, and other machines that will transmits feedback signal to the operator and receives command signals in response, this all done in high speed communication link.
4G Vs 5G Technology:
| Parameters | 4G | 5G |
| Latency | 10ms | 1ms or less |
| Max Data Rate | 1 Gbps | 20Gbps |
| Transmitted Power | 23dbm except for 2.5GHz TDD | 26dbm at 2.5GHz and above |
| No of Mobile Connections | 8 billion | 11 billion |
| Frequency Range | 600 MHz to 5.925 GHz | 600 MHz to 28,39 and 80 GHz (mm wave technology) |
| Channel BW (Band Width) | 20 MHz | 100 MHz for 6 GHz400 MHz for above 6 GHz |
| Uplink Wave form | SC-FDMA | CP-OFDM |
| Download speed | 100 Mbps | 10,000 Mbps |
| Deployment Year | 2006-2010 | 2020 |
| User Data BW (Practical Analyses) | Mobile = 10-30MbpsFixed = 50-60 Mbps (cm wave) | Mobile = 80-100 MbpsFixed = 1-3 Gbps (mm wave) |
| Coverage per Antenna & Usage | Mobile = 50-150 Km (City, Rural area)Fixed = 1-2 Km (High Density Area) | Mobile = 50-80 Km (City, Rural area)Fixed = 250-300 meter (High Density Area) |
How 5G Works:
The cellular networks are actually the cluster of small cells and these cells are further divided into sectors. In 4G LTE, the high power towers of cell are transmitting electromagnetic radiation to cover longer distances. However on the other hand 5G uses small towers mounted at every 1 Km on different types of high elevated places like rooftops and poles in large quantity. These many small cells transmit radiation of the wavelength of the order of few millimeter. These millimeter electromagnetic waves can travel smaller distances and travel in line of sight hence it is hindered by any physical objects like tall buildings and can be disturbed by weather conditions as a result degrading the signal strength.
The lower frequency spectrum of 5G can reach longer distance but data rates will be compromised while mm wave have smaller distance but higher data rates.
(Fig- 5G Cellular Network Base Station Types)
What is mm Wave..?
The millimeter (mm) wave spectrum falls in the frequency range of 30 GHz to 300 GHz. This phenomenal range of frequency has the wavelength of 1mm to 10mm. The mm wave are also known as VHF or EHF Very High Frequency or Extremely High Frequency respectively names given by ITU.
The mm waves are susceptible to heavy rainfall. The mm wave signal strength will drop when heavy droplets of rain interfere with mm wave i.e when the size of droplet or ice crystals reach the size of mm wave which is about few inches, then severe attenuation will be observed. This is also for snowy season with thick/dense blizzards are observed. This phenomenon is commonly known as “Rain Fade” or “Rain Loss”. This phenomenon can affect the satellite communication in LEO, MEO and GEO earth orbits. This phenomenon can also hinder GPS signals. Licensed bands from FCC are 71-76 GHz, 81-86 GHz and 92-95 GHz to operated point-point high BW. Unlicensed band for short range communication can be done on 60 GHz mm wave spectrum
5G Antenna:
Unlike passive antennas that are used in common RF communication which are made of metal rods, 5G antennas are active antennas having semiconductor devices embedded inside the antenna. High speed 5G dedicated PCB design and fabrication is utmost important for 5G antenna PCB and associated circuitry. At Rayming PCB we have developed state of the art 5G PCB. Please check out the snapshot of our 5G PCB.
The basic technique used is the beam forming which allows the 5G antenna to emit radiation in a particular direction or pattern instead of emitting equally in all directions. The 5G antenna is made of massive MIMO (Multiple Input Multiple Output) antennae. The massive / large number of antenna elements are used in phased array shape and different sizes are available. The individual antenna element size is small but are used in 100s to make dense array.
As a result the radio waves are directed to the targeted users with the help of advanced algorithms that determine the best route for radio waves to reach the end user. This phenomenon is known as beam steering. The beam steering is very effective and optimizes the power consumption and increase efficiency by eliminating the unwanted Omni directional radio transmission. As a result very high throughput thus allowing more people to connect simultaneously
5G Technology Applications:
- High Speed Cellular Network
As discussed above, the extremely high data rates enable the calling, messaging and multimedia services to speed up and faster communication is possible. So no worry about call dropping and undelivered text messages or slow internet. 5G technology will give you unstoppable high speed services
- Entertainment and Multimedia:
Now you can enjoy Netflix, Watch Live shows or download your favorite TV program, movies in the blink of an eye. Yes literally..! This is possible because of 5G high download speed up-to 10Gbps.
- Smart Home
The smart devices will be using 5G technology to connect to our mobile devices using wireless network for monitoring and control. High speed 5G connectivity can enable CCTV cameras to transmit live video streaming to our mobile devices
- Logistics
High speed communication 5G link will enable logistics tracking, management and delivery of shipment online on our cell phones
- 5G in Farming
Smart chips like RFID will be used in livestock to track position and activity. Smart agricultural machines can be controlled remotely through speedy 5G link.
- Medical Surgery
Live video streaming inside the patient’s body for transplant and operation is possible today due to 5G
- Autonomous Driving
In future, automatic cars will be on roads. Cars will interact with traffic signals and can communicate with other cars by means of 5G high speed link. This enable those to detect an obstacle in matter of milliseconds (latency of 5G) and to avoid collision.
