As technology evolves, so too does the circuitry behind it.
Until the 2010s, very few people owned wireless devices. The demand for RF PCBs, which these devices utilized, was not high.
Today, nearly everybody has these devices. Whether they are smartphones, sensors, robotics, or security and surveillance devices, the demand for the RF boards that these devices utilize has never been higher.
Thus, it would be a good idea for any PCB manufacturer to learn how to design RF PCBs.
While there are similarities, RF PCBs are designed quite differently than standard PCBs. This guide will explore the difference and show what it takes to create a good RF PCB.
1、What is an RF PCB?
RF stands for "radio frequency." It makes the PCBs a part of operating at a much higher frequency than standard PCBs, starting from 100 megahertz (MHz).
It is a significant difference between RF PCBs and standard PCBs. The issues that surround RF PCB design will come back to this, as micromanaging high frequencies are integral to designing an RF PCB.
Image 1: RF PCB Design
2、Basic Design Concepts of RF PCBs
The higher frequency of RF PCBs makes it more complicated in their creation and design. There are four factors to consider before developing a blueprint for designing an RF PCB.
2.1 Some Constants
The first difference between RF and non-RF PCBs are the constants. Dielectric constants, for example, can be treated as a single value in non-RF applications. But because the frequency of an RF board is much higher, they should be treated as multiple values.
2.2 Temperature control
Due to the higher frequency used in RF PCB, temperatures within the board can fluctuate. If the materials used to create the board are not appropriately placed, these fluctuations can get out of hand.
2.3 Adjacent spacing
The most optimized RF PCBs contain four layers. Constructing a four-layer PCB means that individual components will need to be spaced together in a way where everything can work together correctly.
2.4 Material selection
It is creating a four-layer PCB that has consistent temperatures demands that you choose materials that will allow the least margin for error. Read ahead to discover exactly what these materials are and how to use them.
3、Material Selection for RF PCBs
Choosing the right materials is the most crucial aspect when it comes to RF PCB design. Whether you want to use two layers or four layers, materials will make or break an RF PCB.
There are three things to consider when choosing RF PCB materials.
3.1 The coefficient of thermal expansion
This coefficient pertains to an object's size about temperature changes. Because RF PCBs deal with temperatures that are not only high but variable, this coefficient requires continuous use as a method of micromanaging temperature levels.
3.2 Moisture absorption
Moisture must also be taken into account as water affects temperatures since moisture does affect temperatures. Moisture is directly related to the environment that the device utilizing the RF PCB operates in.
3.3 Cost vs. Performance
If this debate wasn't relevant enough when selecting non-RF PCBs, it is even more relevant when selecting materials for RF PCBs. The best thing to do is to know what your budget is to the penny, then aim to choose a cost-balanced material, electrical performance, and thermal robustness.
4、Optional Materials for RF PCBs
There are many ways to design an RF PCB. While there are required materials, there are many variations of these materials. It is where the options come in..
Polytetrafluoroethylene (aka PTFE), ceramics, hydrocarbon, and various types of glass are necessary, but many combinations are possible.
The following materials are added to these combinations.
Image 2: RF PCB Design
It is the cheapest material that can make any RF PCB. The reason it has received so much controversy is that it cannot handle most of the frequencies that RF PCBs demand.
4.2 Bonding materials
PTFE is a bonding material. No board is complete without this foundation. Like with most materials, there are dozens of options when selecting bonding material. If you plan on soldering, make sure your bonding material can withstand intense temperatures.
4.3 Combining your materials
As mentioned earlier, the optimal RF PCB is typically four layers. It is why there are a lot of options when it comes to selecting and combining materials. Do not forget that when you are designing an RF PCB, you will be dealing with high frequencies and high temperatures. Choose and combine your materials based on this fundamental knowledge.
5、How to Manage the Power in RF PCBs
People often wonder why their smartphone gets very hot when it is on for too long, especially when using apps that use data.
The more data that a device needs to communicate, the more power it needs to achieve these communications.
Remember that RF stands for "Radio Frequency." What does the radio do? It is in a constant state of communication.
It is done by way of something called an RF Module, which receives radio signals between two or more devices. A smartphone contains RF modules.
What is the production of the RF module? RF PCBs, that's what.
Image 3: RF PCB Design
Because there are so many connections at work, electricity must be managed when designing an RF PCB.
While it is straightforward to line up all the materials in an RF PCB close to each other to save time, an RF board will burn out quickly if you implement this policy. Resist this temptation.
Image 4: RF PCB Design
6、Dealing With Loss Tangents in RF PCBs
Because of high frequencies as well as the electricity issues mentioned previously, additional heat during operation is something that must be addressed.
This phenomenon is known as a loss tangent. It refers to a component in a multilayer board that gets dense from additional heat.
Addressing this is done by keeping a close eye on the amplitude of the circuit. The additional heat develops when amplitude levels drop.
7、RF PCB Design Layout Instructions
Because so many things are at work when it comes to RF PCBs, the design layout will affect the stability and reliability of the final product.
Everything in an RF PCB needs to come together, so there is not a lot of crowding, yet nothing is too far apart. These instructions will show you how to do this.
7.1 Arrange RF traces first
RF traces carry the highest frequency of an RF board. These are arranged first because everything else will be placed around them.
Another thing that must be done is to leave adequate space. It will allow smoother bends, and more importantly, it will isolate the RF signal.
7.2 Isolating RF tracking is essential.
After you have arranged the RF traces, you must now design your board such that the RF tracks are isolated. You can do this by stitching vias around the RF traces.
It is essential because it is very likely that the RF board you are designing will be part of a device that utilizes high-speed signals, such as USB and HDMI ports. Isolating the tracks will prevent overheating when these signals are sent to and from the device.
7.3 Keep battery inductance low.
Ground inductance is affected by two things in the RF chipset: Vias and through holes. Vias can accomplish the task of connecting ground pins to the ground plane.
Arranging multiple through holes will also reduce the harmful effects of the ground plane, and this is important because battery inductance does not respond well to high frequencies.
Image 5: RF PCB Design
Leaning about RF PCB Design is going to prove to be a good investment. The future is very bright for RF technology because devices that use RF circuit boards are becoming common.
Designing RF PCBs is much different than designing standard PCBs in that you are dealing with much higher frequencies, higher temperatures that vary a lot, and multilayer design. It means that you must adapt to different strategies when designing RF PCBs.
We know how fast RF PCB technology is growing and are continually finding new information about RF PCB design and the materials and components that they demand. When you are ready to begin designing and creating RF PCBs, contact us, and we will get you started on the right track.