PCB Manufacturing

RF and Microwave PCBs: Components, Materials and Applications

RF and Microwave PCBs

RF and Microwave technology is a very fast-growing business all over the world. In today’s technology, RF and microwave applications are used widely, such as cellphone networks, 5G, smart TV, tablets, telecommunications, automotive, aerospace., etc. RF and microwave PCBs are the base of this technology.

What are RF and Microwave PCBs?

RF and microwave PCBs are printed circuit boards with signals ranging from 50 MHz to 30 GHz. Such PCBs operate in terms of Megahertz and Gigahertz which means from low frequency to very high frequency. This kind of PCB is generally used in wireless systems like cell phone towers to military radar communication systems.

Different Signal  Frequencies between RF and Microwave PCBs and Common PCB

RF and Microwave PCB

Both RF and Microwave PCBs use high-frequency signals. The RF and Microwave signals have a different frequency range. RF and microwave circuits have a fixed frequency band in which the signal travels. The signal contains the information and this signal travels only in a defined frequency range and other frequencies are filtered. The frequencies of different signals are as follows.

  • Low-Frequency Signal:  50 MHz
  • RF Signals: 50 MHz to 1 GHz
  • Microwave Signals: 1 GHz to 30 GHz

Key Components in RF and Microwave PCBs

Dielectric Material

RF/Microwave circuits usually have very precise processes or low-level signal transmission which means this circuit requires very tight tolerance for all the parameters relating to the signal loss. Impedance mismatch and di-electric material in the RF PCBs and microwave PCBs are the main reasons for signal loss. The choice of dielectric material is a major part of the signal energy loss. That means these two parameters are tightly controlled by the material.  The following two are the major parameters for selecting the material and the board thickness.

  • Loss Tangent: Impedance mismatch in the RF PCB and microwave PCB that is referred to as a Loss Tangent.  It is important to know how much signal loss occurs in the design. In other words, signal input and Signal Output.
  • Die-electric Constant: The Impedance value is dependent on the dielectric material thickness and conductor width which controls the power and copper loss. The Heat generated in the circuit needs to be transmitted at any place in the RF PCB and microwave PCB. Heat may be transferred to the material which has a low dielectric constant or the heavy copper circuit which can carry more power.

Transmission Line

A transmission line in the RF PCB and Microwave PCB called the copper traces carried out the electrical signals from one point to another point. This line in RF Microwave PCB carried the signal without noise and interruption to the signal. All the transmission lines carry an impedance value.

Different types of transmission line in RF PCB:

  • Strip line
  • Microstrip
  • Edge coupled microstrip
  • Embedded microstrip
  • Co-planar microstrip

The commonly used structures in the transmission line are the Microstrip and Strip line. See the strip line structure below in which the conductor is placed between the two ground planes.

Strip Line Example

A microstrip line in RF PCB has a different structure than a strip line. There is a dielectric material placed in between the conductor and ground plane.

Microstrip Example

Copper Foil

The loss in the circuit depends on the circuit pattern, metal conductivity and the dielectric material on which the metal conductor is placed.

Current flows on the depth of the copper conductor surface that called skin depth. It measures how electrical current will flow on the conductor surface. The Outer surface is most important in the RF circuit because the current flow is high on the lower conductor surface. See the below example,

High-frequency Current Conductivity

There are four FOIL types used in the RF boards.

  • ED Copper- Electrodeposited Foil

The ED Copper Process

  • RA Copper- Reverse Treated Foil

Cross-section and SEM of RTF Copper Foil

  • Very Low-profile Foil

Cross-section and SEM of Typical VLP Copper Profile

  • RA copper- Rolled Annealed Copper Foil

 

The RA Copper Process

How to Choose the Right RF and Microwave PCBs Materials

Choosing the right material for RF/Microwave technology-related applications is the most critical decision for the success of any desired project. When there need to be choose the right material for any project, Our Engineers are more aware of the PCB RF technology today. Today there are lots of RF materials available in the market which have dozens of controlled Dk and low-loss materials available in the market.

There are different ideas for PCB designers to select the proper material for RF PCB design.

  • Match Di-electric Constant: Di-electric constant (Dk) is an important part of the material. The material contains different parameters that need to match all Dk values Otherwise these can cause problems. To avoid any problem with the material, the designer has to ask the fabricator to choose the proper material to match the Dk.
  • Match Coefficient of Thermal Expansion (CTE): The CTE indicates the value of expansion when heat is generated. Different material has a different CTE value. This is an important factor which can affect the reliability of the boards.
  • Skin Effect: This is one kind of noise generated on the board due to the copper traces.
  • Heat Dissipation: Use the thick core and proper copper layout for the heat sink.

Some Common Types of Materials Used in RF and Microwave PCBs

  • RO3006
  • RO3010
  • RO4835
  • RT/Duroid
  • RO4000
  • 6035HTC
  • XT/Duroid
  • RO4350B
  • RO3003
  • RO4000
  • RO4350B
  • RO4835
  • RO4350B
  • XT/Duroid

Applications of RF and Microwave PCBs

Applications of RF and Microwave PCBs

  • Consumer Electronics: Smartphones, tablets, wireless systems.
  • Military/Aerospace: Radar system, Satellite communication, defence
  • High Power Applications: Amplifier, high-power transmitters
  • Medical Devices: X-ray machines
  • Automotive: Navigation, communication system etc.
  • Industrial: Robotics, Industrial automation etc.

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