What is an RF PCB Board?
The requirements for the circuit board’s performance indicators determine the type of circuit board substrate to use. Either regular FR4 epoxy glass fiber or a specialized microwave substrate like Teflon are acceptable.
Over 100 MHz is the operational frequency of RF PCBs for signals. RF signals with frequencies more than 2 GHz can be found in microwave PCBs, which fall within this category. Radar, sensors, cellphones, wireless transmission systems, and security systems are just a few of the applications that use RF PCBs. RF PCBs have a more sophisticated design than regular PCBs because of the importance of signal integrity, noise immunity, electromagnetic interference, and stringent impedance tolerances.
The field of PCB manufacturing’s radio frequency printed circuit boards (RF PCBs) is interesting and expanding quickly. Your needs can be met at every stage of fabrication and assembly by INTOPCB, a reputable PCB manufacturer, including material selection and important RF PCB manufacturing problems to be aware of.
RF PCB application
Applications for RF boards include robots, wireless technology, smart phones, sensors, and security, among many more. The need for RF boards is increasing as new technologies emerge that are pushing the boundaries of electronics.
To ensure that the boards are manufactured to high quality standards and on time, it is essential to find a qualified RF PCB manufacturer. Our track record is self-evident. We take satisfaction in realizing the most difficult layout concepts.
Key to control RF PCB quality
Since RF signals are particularly susceptible to noise, there is a potential that they could ripple or reflect. The need to adjust the impedance value along each of the circuit’s traces makes impedance a particularly important factor in this class of circuits. Additionally, it’s important to limit the power losses brought on by signal reflections by designing appropriate paths for return current, which, as frequency rises, prefers to take the routes with the lowest inductance. Crosstalk, or the transfer of energy between adjacent traces brought on by inductive or capacitive couplings, becomes increasingly important as the performance and density of the components rise. So if want to make out high quality RF printed circuit board, PCB manufacturer must do correct in below production work.
Routing
The curvature and angles that are present on a trace are subject to the first rule.It is ideal to generate an arc with a radius of curvature that is at least three times the trace width when a transmission line needs to change direction due to routing requirements. As a result, the characteristic impedance is guaranteed to remain constant throughout the curved segment. If this isn’t possible, draw an angle while keeping in mind that right angles must be replaced by two 45° angles.
In order to reduce the resulting variance in inductance, it is advised to install at least two via holes for each crossing when a transmission line must pass through two or more layers.
In fact, utilizing the greatest diameter value feasible with the trace width for the holes, a via pair can cut the inductance fluctuation by 50%. Particularly if they are intersected by sensitive signals, the traces connecting the RF components must be kept as short, appropriately spaced apart, and organized orthogonally on the neighboring layers. The multilayer structure with four layers is the greatest option for the stackup.
The results are far better and are simple to duplicate, even though the cost is more than a double layer method. High frequencies cannot sustain discontinuities in the ground planes, hence continuous ground planes must be introduced beneath the RF signal traces.
Inductance and Impedance
A frequent strategy employed by designers is to select a standard impedance value (usually 50 ohms), so limiting their selection to RF components (filters, antennas, and amplifiers) with this particular impedance.
The 50 ohm value has the benefit of being very common and makes impedance matching easier, enabling each PCB trace to be given the proper width. On the other hand, inductance should be maintained as low as possible because it can significantly affect the design of an RF PCB.This is accomplished by using several through holes, ground planes that are appropriately large and clear of gaps or discontinuities, and suitable ground connections to each RF component. High frequency components and traces need to be placed close to ground planes.
Transmission lines
Transmission lines (such as microstrip, stripline, coplanar waveguide, or others) are needed for RF PCBs in order to prevent power losses and guarantee signal integrity.The characteristic impedance, which typically has values between 50 and 75, is determined by the width of the trace, the layer thickness, and the kind of dielectric in microstrip transmission lines (Figure 1).Striplines are utilized on the inner layers, and microstrips are used on the outer layers.
On the other hand, coplanar waveguides (grounded) offer the best level of isolation, particularly when RF signals intersect relatively close traces. You can use one of the many online calculators to determine the characteristic impedance (and subsequently the width of the trace), but you must be aware of the exact dielectric constant R values for each layer (for instance, an external layer of pre-preg laminate could have a εR = 3.8 while an internal layer of FR-4 has a εR = 4.2).
Material selection
However, FR-4 (flame retardant level 4) and other materials frequently used in PCB fabrication are not the best options for high frequency RF applications due to the non-uniformity of the dielectric constant and a worse tangent angle. FR-4 is also relatively inexpensive. Specific materials, such as FEP, PTFE, ceramic, hydrocarbons, and several kinds of glass fiber, are employed for RF PCBs. The fluoropolymer family’s PFE and PTFE materials enhance the base material’s chemical resistance and feature anti-adhesion, smoothness, and exceptional heat resistance (they can survive temperatures as high as 200°C). The ideal option is PTFE with fiberglass, eventually woven glass fiber, if money is not an issue and quality is more essential than price. The PTFE with ceramic coating is used because it is less expensive and the manufacturing process is simpler.
A major manufacturer of dielectrics, laminates, and pre-pregs for high frequency RF applications is Rogers Advanced Connectivity Solutions (ACS), which supplies materials to several printed circuit board makers. Although more expensive, Rogers materials enable power losses to be reduced by up to 50%, ensuring great performance even over 20GHz and a low dielectric constant value that is stable and reproducible as the frequency varies. The most normal strategy is to use various materials that satisfy the requirements for electrical performance, thermal characteristics, and cost because RF PCBs are frequently multi-layered. For instance, it is possible to employ less expensive epoxy glass laminates in the interior layers and high performance Rogers laminates in the outside layers.
Moisture Absorption
The environment in which your device will operate is another element to take into account. You might not be concerned about the material’s tendency to absorb moisture if the board will be used in a lab with a controlled air environment. However, moisture intrusion becomes a more urgent problem if the board will be outdoors, in the rain, or if it might spend brief, unforeseen travels underwater.
Components ground planes
On the component layer (top or bottom of the PCB), which is positioned directly beneath the component, the majority of integrated circuits call for a continuous ground plane. This plane’s job is to direct the CC and RF signal return currents in the direction of the designated ground plane. The so-called “ground paddles” (Figure 2) also serve the additional purpose of dispersing extra heat, thus appropriate through holes ought to be included. To increase the dissipation effect, these vias should be through holes that span multiple PCB layers, be internally plated, and filled with thermally conductive paste.
Bypass capacitor
The power pins should be in close proximity to the appropriate value bypass capacitors, which can be arranged either singly or in a star pattern. A decoupling capacitor with a higher capacity (a few tens of micro Farads) is positioned in the center of the star arrangement, which is particularly helpful for components with many power pins. Other capacitors with a smaller capacity are positioned close to each branch. Long return pathways to the ground are avoided by the star configuration, which lowers parasitic inductances and prevents the emergence of unintended feedback loops. Given that the capacitor’s self-resonance frequency (SRF) rises above a certain point and takes on inductive properties, the decoupling effect is negated, it is important to pay close attention to this value.
Ground planes
It is standard procedure to place uninterrupted ground planes next to every layer that has components or RF transmission lines. For striplines, it is necessary to have dedicated ground planes both above and below the central conductor. To lessen the impacts of parasitic inductances created by current-back-to-ground paths, via holes can be inserted on RF traces and next to RF components. The coupling between RF lines and other signals traveling through the PCB is also lessened by the use of through holes.
Insulation
It’s important to pay close attention to prevent harmful couplings between the signals. The RF transmission lines shouldn’t run parallel for extended periods of time and should be kept as far apart from other traces as feasible (especially if they are crossed by high-speed signals like HDMI, Ethernet, USB, clock, differential signals, etc.). In reality, as the gap between them shrinks and the distance traveled in the parallel direction grows, the coupling between parallel microstrips grows. Traces carrying high-power signals ought to be segregated from other circuit components in a similar manner. The grounded coplanar waveguides can be used to get a superb insulation value.
In order to prevent coupling phenomena, high-speed signal traces should be routed on a distinct layer than RF signal traces. Additionally, the power supply lines should be routed on specific layers with the proper decoupling and bypass capacitors.
INTOPCB are an experience RF PCB manufacturer, offer you high quality and cost efficient RF PCB manufacturing service for you, contact for pricing for reference right away.
| Capability | |
| Finished inner/outer copper thickness | 1-6OZ |
| Base Material | FR-4 / HI-TG/Aluminum /CEM-1/Rogers/Argon/Taconic/Teflon |
| Layers | 1-40 |
| Min hole size | Mechanical hole: 0.15mm Laser hole: 0.1mm |
| Finished board thickness | 0.2-7.0mm |
| Controlled Impedance | +/- 5% |
| Outline profile | Rout/ V-cut/ Bridge/ Stamp hole |
| Plugging vias capability | 0.2-8.0mm |
| Surface treatment | HASL, HASL lead free, Immersion Gold, Immersion Tin, Immersion Silver, Hard gold, Flash gold, OSP… |