The one thing you need to protect an electronic circuit against is electromagnetic interference. Failure to do so will result in performance issues and could also lead to PCB failure.
It is the Electromagnetic Compatibility or EMC that determines that a device is compatible with its environment.
In order to design PCBs with EMC, some simple design guidelines can come in handy. Some of these include:
PCB Guidelines for EMC
- Referencing high-speed signals to a solid plane.
- Ensuring that the current flow in any trace on a PCB completes the entire circuit loop and comes back to the source through the reference plane.
- Ensuring that the return current follows the path of least impedance.
An important way that takes care of EMI is PCB Shielding.
What is PCB Shield?
PCB Shielding is essentially an effective way of protecting the board against electromagnetic signals. Additionally, they make sure that stronger signals do not escape. In the absence of this, there can be crosstalk, power supply noises, electromagnetic interference and more. Electromagnetic Interference can particularly lead to issues such as disrupted communication, interference with wireless devices, component failure as well as software errors.
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How to implement EMI shielding in your PCB layout?
There are several ways to implement EMI shielding in the PCB layout. Some of these include:
- Metal shielding cans involve the use of a metal box that restricts electromagnetic radiation.
- Elastomer electromagnetic shielding materials.
- Ferrite beads, rods, and plates.
- High conductivity mesh materials.
- Separated ground replacements.
It is important to remember that irrespective of which method you choose you need to follow the best practices when it comes to installing the chosen shielding.
Types of PCB Shielding
There are broadly two types of PCB Shielding:
1. PCB RF Shielding
These work by lowering the coupling of electromagnetic fields & hence blocking electromagnetic radiation & radio frequencies. These shields also include a Faraday Cage.
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2. Arduino Shielding
This shield can be mounted on top of the Arduino board. Particularly Arduino has a wide range of shields for prototyping. These are preferred as they are easy to use and are known to be extremely cost-efficient. Importantly there is a library available with editable codes, that renders the process simple. Additionally, the added advantage they offer is that Arduino shields can be stacked on top of each other. They, therefore, combine different functionalities. An important aspect to be remembered here is that the shields must use the pins of the Arduino board itself as there needs to be a common GND. Arduino Shields placed on Arduino Boards help in wireless communication, motor control, LCD control, connecting to internet frameworks, to mention a few use cases.
Arduino Shields, in turn, are of various types. These include:
- Wireless Shields
- Ethernet Shields
- GSM Shield
- Proto Shield
Attributes of PCB Shield
With a PCB level shield, the following features can be incorporated:
- You can ensure a small footprint.
- Through-hole or surface mount.
- There are ventilation holes.
- Removable covers ensure easy access to components.
- Shock & vibration can be countered with locking mechanisms.
- There is insulation padding.
- low-profile configurations.
- Multi-cavity patterns.
Material used in PCB Shielding
Normally the following material is widely used in PCB shielding:
- Tin plated cold rolled steel
- Tin plated copper
- Nickel silver
- Stainless steel
- Tin plated phosphorous bronze
As a thumb rule, tin-plated steel is preferred if the shielding is below 100 MHz & tin-plated copper is used if it is above 200MHz.
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A Word of Caution
While tin plating is extensively used as it renders soldering easy, the use of aluminum isn’t preferred as it is known to have heat-sinking properties.
To sum up
PCB shielding is the much-needed protection that your circuit requires. Depending on your frequency range, you need to choose the best-suited material. With RF PCB shields you can also block out radio frequency.
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