metals for RFI shielding
EMC /RFI shields are essential in protecting sensitive equipment from damage caused by electromagnetic interference from nearby devices. They are particularly valuable in industries such as defence, communications, healthcare and aerospace.
Due to the important role RFI shields play in so many critical areas, it is crucial that the right material is used for the intended purpose and environment. This is defined by the electronics being protected and the frequencies that need to be repelled. There are multiple factors to take into account, including strength, corrosion resistance, temperature tolerance, durability – not to mention, cost.
To meet the very latest Electromagnetic Compatibility (EMC) directives, we offer a number of shielding solutions, including standard and custom cans, fences and enclosures, multi-cavity labyrinths and our own TECpack “on the bench” modelling system.
Here we are considering the benefits of some of the most common metals for RFI shields:
nickel
Nickel and its alloys are popular EMC /RFI shielding materials in low-frequency applications. It is durable, corrosion-resistant and demonstrates excellent mechanical properties including strength, high-temperature tolerance, and versatility.
aluminium
Strong but lightweight, reliable and versatile, aluminium is an excellent conductor of both electricity and heat. It is a popular choice for industrial components.
Aluminium is available in a number of grades offering corrosion and fatigue resistance and can be anodised. It is also relatively inexpensive as its low density allows for thinner sheets with the same strength as thicker sheets made from other, heavier metals.
Key benefits:
- affordability
- durability
- lightweight
- versatility
brass
An alloy of copper and zinc, brass is often seen used in shielding across electrical contacts and connectors, medical devices, RF connectors, and relays.
Key benefits:
- affordability
- electrical resistance
- corrosion resistance
- wear resistance
- high-temperature tolerance
- formability and machinability
- compatibility with finishing treatments
gold
Gold is resistant to corrosion and oxidation with a high melting point and is durable under harsh conditions including high temperatures and moisture. This, and because it is dense but very thin, gold is often used in places where space is limited -e.g. smartphones.
Here at Tecan, we see a demand for gold plating of RFI shields, particularly where they will be used in high frequency environments. This is because gold’s conductivity increases with frequency, making it especially effective in applications where radio frequencies such as mobile phones or WiFi routers are used.
materials vs frequency
Traditionally bright tin plating was used for RFI shields, however with the implementation of the RoHS directive on hazardous substances the PCB board assembly lines have switched to non-lead solder, which has a reflow temperature equal to or in excess of the melting point of bright tin, bringing about a general change to nickel silver.
Alternative plating finishes can be used, such as silver or gold, but clearly these can be cost-prohibitive.
At low frequencies where the interference is usually magnetic, the use of specialist materials such as Mu metal or radio metal are more common, although some shielding can be provided by the use of thicker steel or phosphorous bronze.
The frequency limitation of thin metal fabricated shielding is usually between 3 to 5Ghz, beyond which two effects may limit the shielding effectiveness or its usefulness.
Due to the effect of stray capacitance between the enclosure and the electronic components on the PCB any minor movement in the metal of the enclosure could cause microphony to occur, at these frequencies shielding usually takes the form of machined-from-solid which will overcome this effect.
why use chemical etching for RFI shields?
Chemical etching from Tecan allows for precise and intricate designs to be achieved with high accuracy. It ensures that shields are consistent in depth and uniformity, which is crucial for their effectiveness in blocking electromagnetic interference. Performance is further enhanced as chemical etching results in burr-free edges – essential to maintaining signal integrity and meeting stringent requirements for electromagnetic compatibility.
Additionally, chemical etching is a cost-effective manufacturing process, especially for producing RFI shields in large quantities. The ability to create complex patterns and shapes with minimal tooling costs makes it a favorable choice for many industries.
- faster production cycles
- minimal tooling costs
- design flexibility
- inclusion of complex patterns and shapes (e.g. features like access holes, ventilation, fold lines, logos, and part numbers) at no additional cost
- short timescales, even at high volume
- cost-effective
