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By Mark Swanson on  5/25/2017

Die Cut EMI Silicones for Shielding and Sealing: What Engineers Need to Know

Die Cut EMI Silicones for Shielding and Sealing: What Engineers Need to Know

Die cut EMI silicones combine protection against electromagnetic interference (EMI) with electrical conductivity and environmental sealing. They’re filled with metal or metal-coated particles, but are still soft enough to support gasket compression. These die cut silicones also provide good tensile strength and can be reinforced with an inner layer of conducive fabric for increased tear resistance. For electronic designs that require a slimmer profile, sheet materials as thin as .009” are available.

For engineers who need die cut EMI gaskets, selecting the right fill type is especially important. Historically, conductive silicones have been filled with silver or silver-coated particles. Silver can be expensive, however, and is subject to extreme price fluctuations. Other fill materials can’t match silver’s electrical conductivity, but choosing the right shielding silicone is about balancing all of your application requirements. That’s why JBC Technologies die cuts EMI silicones with various particle fills.   

Material Costs

As the following table shows, die cut EMI silicones can be filled with silver, silver-coated, or non-silver particles. Note that EMI materials with silver-coated or non-silver fills can cost significantly less. 

Filler Type Cost

Silver

$$$$$

Silver-Aluminum

$$$$

Silver-Copper

$$$$

Silver-Glass

$$$

Nickel-Graphite

$$

Carbon Black

$

 

Electrical Conductivity

Cost control is important, but engineers need to understand the trade-offs in choosing a less expensive material for applications such as automotive electronics. As the table below shows, EMI gaskets with silver-coated particles still provide excellent electrical conductivity. Die cut EMI silicones that contain nickel-graphite are electrically conductive, too. 

Filler Type Electrical Conductivity

Silver

Extremely Conductive

Silver-Aluminum

Super Conductive

Silver-Copper

Super Conductive

Silver-Glass

Very Conductive

Nickel-Graphite

Conductive

Carbon Black

Semi-Conductive

 

Shielding Effectiveness

Direct methods for measuring shielding effectiveness can be expensive and complex. That’s why volume resistivity (VR), a method for indicating EMI shielding effectiveness indirectly, is often used instead. As the following table shows, die cut EMI silicones with pure silver particles provide the greatest VR. Depending on your application requirements, however, VR levels from other particle fills may be suitable.     

Filler Type Typical VR (ohms/cm)

Silver

.0009

Silver-Aluminum

.003

Silver-Copper

.003

Silver-Glass

.006

Nickel-Graphite

.01

Carbon Black

8.0

 

Other Important Considerations

Finally, design engineers need to choose die cut EMI silicones that meet application-specific requirements for durometer, tensile strength, elongation percentage, and tear resistance. With our strategic network of silicone suppliers, JBC Technologies can help you to select EMI gasket materials for automotive industrial, and other applications. JBC can also save you time and money by converting continuous rolls of EMI shielding materials and then die cutting gaskets that support your assembly operations.

Are you ready to learn more about die cut EMI silicones? For more information, contact JBC Technologies.

Silicones

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