Each of these gasket filler materials comes with its own unique properties and price point. In other words, some of these fillers will only be compatible with particular devices and budgets.
The other major choice you will have to make when selecting materials for your EMI gasket involves the base of the gasket — the material that surrounds the filler and effectively plugs the opening you are trying to cover in your design. The materials used for EMI gaskets overlap with many of the common materials used with non-EMI shielding, standard gaskets.
Silicone is a widely available, affordable and common gasket material, and it’s often found in EMI gaskets. Because of its high degree of flexibility and easy cutting, silicone can be used in a wide variety of gasket applications and made conductive by an appropriate filler material.
However, exposure to oil, fuel, sunlight and corrosive chemicals can degrade silicone relatively quickly. Degradation of the silicone in an EMI gasket can compromise the gasket’s ability to shield its device from EMI, as well as reducing the sealing capabilities of the gasket as a whole.
For that reason, silicone EMI gaskets are most typically used in connector ports inside electronics or on circuit boards. Filler materials used in silicone EMI gaskets typically include silver, aluminum, nickel and copper.
Fluorosilicone solves many of the problems a silicone gasket might encounter in harsh conditions.
Although it is more resistant to harsh environments than silicone, fluorosilicone is still commonly found in internal circuit board applications. This material is often paired with the same fillers as silicone: silver, aluminum, nickel and copper.
Ethylene Propylene Diene Monomer (EPDM)
EPDM is a synthetic rubber that brings high resistance to environmental factors. This material is much more resistant to caustic chemicals like acetones, hydrocarbons and detergents.
This resistance to corrosion and chemical exposure is checked, however, by a lower resistance to high temperatures when compared to silicone and fluorosilicone, as well as poor resistance to oil exposure.
Foam and Fabric Over Foam
This type of gasket material departs from the standard method for introducing conductivity. Instead of filling the gasket with a conductive metal, engineers spray polyurethane foam with nickel or copper to make it conductive. In some cases, a foam-based EMI gasket will have a fabric or wire mesh placed over it.
This style of EMI gasket is only compatible with low closure force environments. Also, keep in mind that, while most EMI gaskets do not provide a strong environmental seal, this style may be particularly vulnerable to water and similar exposures.
Beryllium copper is a high-performance metal that can be fabricated in a variety of shapes. If your design involves repetitive opening and closing of the opening the gasket will cover, beryllium copper may be a good option because it has a high compression set. This metal protects against a wide range of signal frequencies and does not require a filler material like silver or nickel graphite.
Considerations for Choosing EMI Gasket Materials
Form, function and cost are the key considerations you should have in mind as you choose your EMI gasket materials. Often, as you adjust for one factor, another factor becomes more difficult to deal with. In other words, you will have to commit to a balancing act as you choose your materials.
For example, if you are set on silver as the filler for your gasket, prepare to pay high prices because this is the most expensive filler. You may then want to adjust by choosing a lower-cost base material to stay within budget. Below, we look at some of the other key considerations when choosing EMI gasket materials.
Form-in-Place Gasket Materials
There are instances where you’ll have either small, intricate gaskets or the need for a three dimensional gasket rather than a two dimensional gasket made from a single sheet of material. Form-in-place gaskets and extrusions are often the two choices to fill this need.
When in this situation, one of the first questions you should ask yourself and answer when designing an EMI gasket is whether you are going to go with a form-in-place (FIP) gasket or an extrusion. An FIP gasket is dispensed directly onto a part as a liquid so that it forms a seal that fits the exact specifications of the housing, making up for any imperfections on the housing.
The chief benefit of an FIP EMI gasket is that it reduces waste. The gasket is bonded to the surface of the housing and fits it exactly, so there is no cutting or adjusting that leaves expensive EMI materials on the floor. Additionally, if your gasket needs to take a highly complex or intricate shape or fill a very small space, FIP is likely to be the solution you need.
Cost and reduced waste are enormous benefits of FIP gaskets for EMI applications, but a real drawback can materialize if you need your gasket to both protect against EMI and provide a reliable environmental seal. In almost all cases, an FIP gasket can do a good job of only one of those applications — not both.
Extrusion Gasket Materials
Extrusion gaskets are created by feeding the gasket material through a die. The material is dispensed in the appropriate shape to fit the design, but someone must still cut it to the appropriate length, apply it to the housing and bond the two ends together to complete the seal.
Some extrusion gaskets can do a good job of both EMI shielding and environmental sealing. These gaskets also typically perform better in scenarios where the hole must be reopened frequently — they are more likely to “re-bind” and create an effective seal upon closure.
However, this method of EMI gasket production can lead to more waste when you are cutting the gasket material to fit the specifications of your design, and it adds a step to the assembly process. Instead of dispensing the gasket directly into the housing and letting it cure as you would in FIP, you must actually apply the extruded gasket to the device.
Importance of Working with an Expert
The properties and manufacturing processes involved with each EMI shielding gasket material are different, and sometimes the interactions between gasket material, filler and housing can be hard to predict. In other cases, you may choose materials that are unnecessarily expensive or design a gasket that is unnecessarily large.
These kinds of setbacks can cause it to take significantly longer to manufacture your final product, completely sink a design, or make it impossible to produce on any kind of larger scale. That is why so many engineers and designers turn to an EMI shielding expert when designing their EMI gaskets. The expert team at Modus Advanced encourages designers to get them involved early in the design phase to allow for feedback and recommendations before too much has been invested in a design that ultimately won’t work the way it should.