Custom shielding is fast becoming a thing in the electrical and PCB industry.
It’s because most devices today come with digital circuits.
The digital circuits have semiconductor devices. And these devices operate at high frequencies.
But that’s not all.
These high frequencies emitted by these digital circuit boards could be harmful.
That’s the reason why custom shielding is essential.
Hence, we’re going to be talking extensively about it in this article.
And some of the points we’re going to dwell on are:
- The definition of custom shielding
- The different types of custom shielding
- Methods used to reduce EMI with custom shielding
- And the advantages of custom shielding
So, if you want to know everything about custom shielding, stick around.
1. What Is Custom Shielding?
Custom shielding is the act of customizing EMI shields or RFI shields to do the following:
- Reduce the transmission of electromagnetic waves
- Avoid intrusion in sensitive electronic devices
In other words, these EMI shields curb electromagnetic waves. That is, it stops electromagnetic waves from leaving or entering a device. On the other hand, RFI shields prevent radio frequency intrusion.
But why is this so?
The reason is that most electronic devices produced these days emit electromagnetic waves. And if these shields are absent, the electronic devices could malfunction.
But that’s not all.
EMI radiation could be harmful to humans, especially in the aeronautic or automotive industry.
So, custom shielding is useful for the following:
- Aviation electronics
- Medical devices
- Automotive components
- Security devices
- Military electronics
- Computer electronics
- Telecommunication equipment
Considering Frequency Level
You need to consider two things before choosing a custom shield. So, they are the harmonic and operating frequencies.
Some frequencies range from a few Hertz to above 50 GHz.
So, that’s why you need to check the type of metal used. And it’s because there will be an impact on the EMI or RFI shield’s performance.
For instance, if you’re creating a shield against 15 MHz frequencies or lower, use steel.
Why should you use steel?
The reason is simple.
Steel is a ferromagnetic metal. And it’s the most ideal for bulk material effect. Plus, this shielding is for low frequencies.
Hence, it’s different when the attenuation is more significant at lower frequencies. And the ideal metals for these frequencies are those with low core losses and high absorbency. A perfect example of such metals is the MuMetal and Permalloy 80.
But in a situation where the frequencies are above 15 MHz, the shielding becomes:
- A significant amount of a conductivity effect
- A smaller amount of a bulk material effect
When the harmonics and frequency exceed 900 MHz and more, any metal can work. Plus, you can use metals like the following (assuming a depth 0.05mm or more):
- Nickel Silver
Eventually, it all boils down to the standard base materials you decide to use.
2. Standard Base Materials
We’ve already listed a few metals that engineers use to create custom shields. But there are three standard base materials used for shielding:
Copper Alloy 770
Alloy 770 has three key components: Zinc, Nickel, and Copper alloy.
But that’s not all.
The Alloy 770 is ideal for custom EMI gaskets and shielding. Also, this material is useful for corrosion resistance.
And there’s more.
The Alloy 770 also comes in handy for MRI related applications that require no magnetic components.
This material is an ideal choice for shielding. The reason is that aluminum is a non-ferrous material. Hence, it’s extremely conductive. Plus, it’s almost 60 percent more conductive than copper. And it has a remarkable strength to weight ratio.
However, engineers must pay much attention to this material. And it’s because of its oxidation and galvanic corrosion when in use. Plus, it has some fabrication issues.
Pre-Tin Plated Steel
Are you looking for a very affordable solution? Then, you should use this material. It’s ideal for lower KHz frequencies in the lower GHz array.
But there’s more.
This material is not prone to rust because the pre-tin plated steel has high corrosion resistance. And it has a super solderable surface.
3. Types of Custom Board Shielding
Here are three types of custom board shielding:
3.1 One Piece Surface Mount
This custom board shield comes in two options:
- The first option comes as covered
- The second option comes as vented
So, the covered option doesn’t require vents nor access to internal parts—needed for repairs.
Whereas, the vented is suitable for the following applications:
- Where they require air passage
- Where they don’t require internal components
3.2 Two Piece SMS
The two-piece SMS also comes in two options:
- Low-Profile SlimShield
- Spring Finger
And these two options have configurable PDF sales diagrams.
The SlimShield is a two-piece board level shielding line. And it’s a low-profile piece. Hence, it comes with a dented cover that clicks into etched holes on the fence. Plus, it provides shield heights that are as low as 0.060 inches.
But there’s more.
The photo etching process offers speedy delivery and wide-ranging design freedom.
Also, its standard hollow tooling provides the various open locations. And at a low price, it offers excellent cover holding.
This option comprises an exclusive spring finger design attachment amid cover and fence.
Engineers can use this Spring finger design to customize any configuration like:
- Irregular Shapes
Plus, brass and tin plating are the standard design components needed. And they are relatively easy to find.
3.3 CBS 2
The CBS 2 shield has a 6-sided custom shield. And its standard base materials are:
- Alloy 770 Shapes (Rectangle, Square, T and L shape)
- Pre-Tin Plated Phosphate Bronze
- Mercury Metal
- Pre-Tin Plated Steel
This shield comes with input-output cutouts, also known as mounting hardware for PCB. And they help to lock ventilation and dimple holes.
4. PCB Methods to reduce EMI
The best method to terminate interference is by finding the source early. That way, it helps you sort out the issue before you go too far in the design course.
So, here are three crucial steps that are necessary to detect the interference early:
1. Use the smaller conductor trace between VCC pins and the power layer at the PCB level.
Then, reduce the common-mode interference. And you can do this with 4-5 mil pre-peg within the circuit layers.
Also, ensure to keep all the power layers close to the ground layer. Then, add all signal traces to similar circuit layers.
2. Now, divide the circuit layers into high voltage segments like:
- Switch mode supply
- Bridge Rectifiers
- And many more.
And divide the low voltage segments like:
- Signal conditioning circuits
- Modulation circuits
- High-frequency amplifier
Afterward, combine the filters of each unit closer together.
3. The next thing to do is to keep traces far away from the PCB edge. Also, keep track of the PCB width. You should ensure that the PCB width is small. That way, you’d be decreasing its resistance.
Hence, use about 135 degrees corner trace. While you’re at it, it’s best to ensure that the signal tracks are small.
Also, digital GND and analog GND should be apart.
5. Advantages of Photo Etched Board Level Shielding
Here are a few benefits of photo-etched board level shielding:
5.1 It takes away the high expenses of creating tools.
5.2 Boosts design flexibility.
5.3 It produces sophisticated etched nomenclature and logos without spending a dime.
5.4 Enables the mounting of pin designs available in every configuration.
5.5 It makes available slots and through holes for heat dissipation without any cost.
5.6 It provides intricate geometry without any impact on the cost of tools.
5.7 There are internal dividers for multi-cavity usage.
So, with the information in this article, you should have one conclusion. Custom board shields are vital for today’s electronic devices.
But that’s not all.
The EMI shielding and RFI filtering of frequencies help to reduce interference.
Hence, if you want to get more information about custom shielding, feel free to reach us. You can also air your thoughts in our comments section.