Some Printed Circuit Boards (PCBs) perform more than the others do. While the optimization process could be one of the reasons, the use of microwave signal PCB is also another important factor.
In this article, we explain some of the reasons why the microwave signal circuit boards tend to offer some of the highest frequencies you can find out there.
What is Microwave Signal Circuit Boards?
There are different explanations as to what this type of circuit board does. Here are some of the different ways to look at it.
The Range Specifications
The first definition is that the microwave signal PCB are used with and for the signal frequencies that operate in both the microwave and Radio Frequency (RF) ranges. To that end, you can be sure that the frequencies would bolster the applications that operate or use a similar frequency or range.
The second point is that the microwave signal circuit boards are described based on the composition of the components or parts that carry either the microwave or RF signals.
Despite the possibility of these parts to have the RF and microwave signals, it is also possible to spot some differences. Some of these differences are:
- The differences in the components makes the microwave signal PCBs quite better than what is obtainable from the other circuit boards.
- The signals obtainable from either the RF or microwave circuit boards tend to vary or differ, by the frequencies they use or operate.
The Applications Define the Microwave Signal PCBs
You can also say that a circuit board uses the microwave or RF signal if it is used for specific applications. They are commonly used with the high-end industrial applications, such as the following:
- Cellular or telephones
- Networking applications
- Communication apparatuses and;
- Military radar applications
How are Microwave Signals Passed?
The fact that the signals are passed or moved in the form of a wave is one point. However, we want to go deeper to talk about some of the processes involved in making this signal transmission possible.
Here are some of the things you need to know:
- The signals are passed or transmitted between the devices. This transmission process is in place as a way of sending and receiving information. The following are some of the data types that can be transmitted in the process: encoded, audio and video data.
- It is also possible to transmit these signals through the air, in the form of waves or Radio Frequency (RF).
Microwave Signal PCBs vs. Traditional PCBs
There has to some differences between the workings of traditional circuit boards and those of the microwave signal PCBs. The following are some of the discrepancies:
- The types of materials used for the design serve as the major difference. While the microwave signal PCBs use special materials, such as Rogers, Arlon, Teflon and GETEK, non-special materials can be used for the traditional circuit boards.
- Uniformity is also a thing with the microwave signal PCBs, whereby the uniform signal propagation process is used for the microwave and RF frequencies.
Substrate Material Considerations for the Microwave PCBs
The substrate material, which serves as one of the bases for the board, is one important consideration for the designs.
Sometimes and for some good reasons, you may be unable to choose the right materials. However, with the tips below, picking the right substrate material for your microwave signal PCB wouldn’t be an issue any longer.
1. Copper Adhesion
Making sure that copper adheres as expected is one factor that makes all the difference in the microwave signal PCB’s material selection.
The adhesion of the copper coil plays an important role in the reduce the chances of permanent damages, especially in the manufacturing and application environments for the circuit board.
2. Anti-Radiation Resistance
The microwave and RF circuit boards are commonly applied or used in the environments where they are exposed to some damaging tendencies.
Most times, if these circuit boards are to be applied to the nuclear or space applications and devices, there is a tendency that massive iodizing radiation would be obtained.
To this end, the choice of a substrate material should be based on how the material would potentially do the following:
- The accumulative effect of the substrate materials should be ensured, as this potentially increases the circuit board’s performance and lifespan.
- The chosen substrate materials should be capable of potentially reducing the massive ionizing radiation the microwave signal PCB is exposed to.
3. Conformability Considerations
Would it be possible for the microwave signal PCB’s substrate material to be “conformable?” Conformability in the sense refers to the ability of these circuit boards to be made into other forms.
The following are some of the bendability options worth considering:
- The ability of the substrate materials used in the microwave signal PCBs to be conformed or made into other forms, such as cone and cylinder bending shapes.
- The potentiality of preventing or reducing the exposure of the copper foil from getting damaged.
- Ensure that the chosen substrate materials used for the thin circuit boards, can be bent to lower curvature radius.
4. Validate the Material’s Mechanical Performance
The mechanical performance of the microwave signal PCB’s substrate materials is directly proportional to the extent of the protection it offers.
In this regard, it is better to go for the thermoset or rigid substrate materials, which are less susceptible to distortion, warping and bowing.
5. Resistance to Humidity
It is possible for the substrate material to be less susceptible to humidity? This consideration should be taken seriously if the microwave signal PCB is going to be used to exposed to the high-humidity areas or environments.
6. How Much Does It go for?
The cost of the substrate material is another important factor worth considering. It is better to work within your budget and find ways to make a few compromises to get the desired properties and results.
To make the selection process easier for you based on the cost, here are the things to have in mind:
- Thin per unit area substrate materials cost less.
- If you are looking for the best-performing substrate materials, go for the thick per unit area variants. The downside is that they cost a lot more money than the thin per unit area.
The Types of Materials to Use for Microwave or RF PCBs
Now that we have talked about some of the considerations for the substrate materials, let us talk about some of the options before you.
Below are some of the common types of substrate materials you can use to build the microwave signal PCBs:
1. Filled PTFE Composite Laminates
These are the substrate materials commonly used for the high-frequency capabilities. The Rogers PCB materials fall into this category.
The following are some of the additional features of the Filled PTFE or the random glass composite laminates:
- These materials possess the low outgassing properties, which are mostly preferred for the space-centric devices or applications.
- Ceramic-Filled PTFE Composites: these are the substrate materials known for the exceptional mechanical and electrical stability they have to offer. Although Rogers materials are commonly used here, you can also find the Taconic materials ideal for use too. For emphasis, the Taconic RF series and the Rogers RO3000 series are some of the series of substrate materials worth using for designing the microwave signal PCB.
- Hydrocarbon Ceramic Laminates: these are the low-loss microwave signal PCB materials used for the streamlined properties and the ease-of-fabrication they offer over the traditional PTFE substrate materials.
- Megtron 6 Materials: the properties include higher heat resistance and ultra-low loss. These microwave signal PCB substrate materials are ideal for the high-speed applications and the High-Density Interconnect (HDI) applications.
- Woven Glass Reinforced PTFE Laminates: these dedicated substrate materials offer more dimensional stability than the chopped fiber reinforced PTFE composites. They are also lightweight.
Downsides to Working with the Microwave Signal PCBs
It may not be a good idea to design a microwave PCB due to some of the pressing issues. Here are some of the common disadvantages or downsides you tend to notice about these PCBs.
1. Absurd Layout
This refers to the imbalance in how the layout is made. If the layout is not well-layered or put in place as it should, you can be sure that the design would become flawed.
2. Noise Interferences
Noise interferences are one of the common challenges that the microwave signal circuit boards have. This is due to the overt sensitivity of the microwave signals that are more sensitive.
The increased sensitivity also means that the high-speed digital signals can potentially aggravate the risks of noise exposure.
At this point, let us talk about some of the types of noise interferences noticed in the microwave signal PCBs:
- Band Limited Noise: this refers to the noise limitations or interferences, arising from the limitations in the frequency band. These limitations arise by the circuit it passes through or the filters.
- White Noise: this refers to the generalized noise, added to all of the frequencies, at an equal rate.
- Pink Noise: unlike the other noises that tend to produce a flat response, the pink noise doesn’t. Instead, it oscillates or increases with an increase in the frequency.
Sources of Noises in Microwave Signal PCBs
Below are some of the common sources or mediums through which different kinds of noises are generated for the microwave signal PCBs:
This type of noise occurs when a junction diode starts to operate close to the point of avalanche breakdown.
Peculiar to the Radio Frequency (RF) signals, this type of noise can come in the following forms:
- Manifestation of sidebands within the signal. This manifestation allows the phase noise to be spread to each side of the carrier or signal.
- It can also take the form of fluctuations.
- Phase noises can also come in the form of phase jitters.
This type of noise is mostly caused by the flow of current in the signals. Although it is a bit difficult to tackle, you can be sure that it is limited to barrier diodes and tunnel junctions.
Getting Started with Microwave PCB Design: Guidelines to Follow
Sticking to the following guidelines or laid-down procedures can potentially aid in the optimization of the microwave PCBs to offer the best services:
1. Distance the RF Lines
We can say that a microwave signal PCB is “cross-talking” when it has the Radio Frequency (RF) lines closer or clustered.
To this end, it makes sense to go for the signals that are distanced from the RF lines.
2. Zero Current Trace Overlapping
The current traces might be subject to overlapping, but that can be avoided when the return current traces are not overlapped with either the microwave signal blocks or the Radio Frequency (RF).
3. Make Multilayered PCBs
It is important to note that multiple layers or the usage of more than one layers is required for the microwave signal PCB.
For this structure or stackup, the following guidelines should be followed to the latter:
- Make sure that one of the layers is used to make the top layer. This is where the following will be placed: the components, the power stage and the Radio Frequency (RF) signal lines.
- The other layer is to be used for the ground part. Here, the ground layer is positioned below the (top) layers that houses the microwave signal lines and the RF lines.
4. Capacitance Avoidance
Capacitance can be avoided in the microwave signal PCB, only if low-impedance solid ground plane is utilization. This works best when building-up at the sensitive nodes.
5. Component Separation
It is almost important to keep some parts or components separated. This should be greatly considered if it is a multi-faceted circuit board that supports the following types of components:
- Digital components
- Low-level analog parts and;
- Radio Frequency (RF) components.
In conclusion, a microwave signal PCB can help in facilitating the movement of signals in the advanced and high-end industrial applications.
The secret to getting the best results with this is by making sure that the right components are used and that the fabrication requirements are met.