EMI gaskets are designed to minimize or entirely prevent the interference of electromagnetic waves. Prevention of these waves are critical for many reasons. First, electromagnetic disturbance can negatively affect the function of an electrical circuit. Electromagnetic disturbances can be both frustrating and damaging. Electromagnetic radio-frequency interference may over time degrade the performance of the circuit, or even cause the circuit to cease functioning entirely. In reference to the data path, effects from electromagnetic disruption may range from error increases to loss of all data. Clearly, this would be detrimental to multiple operational processes. Automobile ignition systems, mobile phones, and televisions are all affected by electromagnetic disturbances. Certain radio technologies are also particularly susceptible to electromagnetic disturbances. All electronic devices radiate some form of electromagnetic interference. The importance of high-quality EMI shielding gaskets can not be understated and EMI shielding is necessary to the success of multiple products, projects, and operational processes.
Custom Die-Cut EMI Gaskets – Spira Manufacturing Corporation
Custom EMI Gaskets
Electronically Conductive Rubber
Electromagnetic shielding gaskets are made of conductive rubber, also called conductive silicone. Generally, electronically conductive rubbers are known for their excellent weathering, oxidation, and ozone resistance abilities. Electronically conductive rubber is extremely well-suited for use in electromagnetic shield gaskets.
Conductive rubber is made by combining small conductive metal particles through the material and provides both a watertight and an EMI resistant seal. Electronically conductive rubber has great conductivity across its entire surface, excellent electromagnetic protection, easy die-cutting, kiss cutting, and slitting, and can withstand temperatures between -60 to +185ºC in most cases. In certain situations, rubbers can tolerate temperatures as high as 220ºC. Conductive rubber can be put to many industrial purposes and understanding its use in EMI gaskets is important.
Infusion of Rubber
Conductive rubbers can be infused with silver, nickel, silvered aluminum, silvered glass, and graphite. In commercial use, nickel graphite conductive rubber and graphite conductive rubber are often chosen due to their lower costs. In military and aerospace applications, silver copper silicone conductive rubber better meets the Mil-G-83528C required specifications. The military and aerospace industry may also choose to use fluorosilicate versions of rubber due to its chemical and fuel resistance.
Since various materials and installation methods are available, it is important to consider which materials and methods are suitable for the desired application. Chemical compatibility is essential, so it is crucial to make note of what material should be used to construct the gasket relative to the environmental factors that the gasket will be exposed to, such as high or low temperatures, rain or wind, solvents, and other conditions. Installation of a gasket can involve the use of PSA’s, epoxies, or fasteners, all of which could factor into the overall cost of the gasket. Gasket manufacturers will be willing to work with you in determining which options should be taken.
High Frequency Protection
Electronically conductive rubber can provide protection from high frequencies. Frequencies can range from 60 dB at 30MHz to 10GHz. Conductive rubber is well-suited for military communications because of its excellent conductivity, electromagnetic shielding, and grounding. Electronically conductive rubber is easy to shape and mold and can come in sheets, o-rings, die-cuts, parts and more. Conductive rubber can also be custom-made if it is needed for specific uncommon applications.
Electronically Conductive Rubber Types:
- Silicone Carbon
- Fluorosilicone Nickel Graphite
- Silicone Nickel Graphite Flame Retardant
- Silicone Silver Aluminium
- Fluorosilicone Silver Aluminium
- Fluorosilicone Nickel
- Silver Plated Nickel
- Silver Glass
Electronically Conductive Plastics
Recently, electronically conductive plastics have been introduced into the EMI shielding industry. Plastics of this nature can be made electronically conductive by the addition of carbon nanotubes, steel fibers, or conductive fillers. Materials are usually added during the plastic molding process. Electric grounding and electric switches also may utilize these types of conductive plastic. Previously, shielding gaskets were, for the most part, made using conductive metals. This practice was effective to an extent, but made gaskets heavier and less cost effective. For this reason, some manufacturers have chosen to use electronically conductive plastics in their shielding mechanisms. Some of the many advantages of conductive plastics include enabling the fabrication of gaskets that are less expensive and more reliable. The only significant disadvantage of conductive plastic is its sensitivity to extreme temperature. When exposed to temperatures like this for long periods of time, electronically conductive plastic may begin to experience difficulties. For instance, prolonged exposure to high temperatures may cause plastics to melt. In the same way, exposure to very cold temperatures tends to cause conductive plastics to crack or fracture. Despite these disadvantages, many applications are well suited for the use of electronically conductive plastics.
About RF Gaskets
With certain frequencies, usually above 500 MHz, traces become electrically longer. RF gaskets also tend to be higher above the plane. There are a few measures that can be taken at these frequencies to reduce electromagnetic disturbances.
One of these is wave shaping. Wave shaping is done by using a series of resistors and embedding the traces between two planes. If there is still too much EMI after the wave shaping process, these gaskets may be used. RF gaskets are usually used in conjunction with copper tape.
Types of EMI Gaskets
Gaskets are composed of electronically conductive rubber but can also be designed to include a variety of different materials to make them more effective in each of their applications. Some of these are solid, sponge, and fabric-reinforced materials. Gaskets can come in virtually any size or shape, depending on the materials that are used. EMI shielding gaskets generally range from diameters of 0.250" to 60" with thicknesses starting at 0.003". When choosing the right type of gasket, the goal is usually not only to reduce EMI interference but to minimise the number of screws or fasteners needed to comply with shielding requirements.
Understanding some of the commonly used gaskets and their shielding capacities is important. There are a few different types of Shielding gaskets, two of which are groove mounted gaskets and surface mounted gaskets.
Grooved Mounted EMI Shielding Gaskets
One common type of gasket is a grooved mounted gasket. A grooved mounted gasket is placed in a groove where it is machined, extruded or cast for sealing into a system. Grooved mounted gaskets are wound out of spring temper beryllium copper in order to provide compression resistance and spring memory. High-shielding material is great for military and aerospace applications and tends to solve problems that other shields are unable to. Gaskets of this kind usually offer shielding quality of up to 165 dB depending on their application and are a great choice for many commercial industrial applications. Similar shields can be for FCC and European Community EMI shield requirements. Die-cast or molded "pinch boss" grooved gaskets can offer a shield of 95 dB at 1 GHz and are highly durable.
Multiple Sealed Grooved Mounted Gaskets
Multiple sealed gaskets are combinations of EMI and environmental gaskets. Multiple sealed gaskets can be perfect for applications that need quality sealing and have limited space or require a groove-mount solution. These gaskets tend to offer shielding from 86 dB to 165 dB.
Stainless Steel Silicone Grooved Mounted Gaskets
A few grooved gaskets are constructed of stainless steel as a main component in addition to a silicate compound. These are commonly low closure force shields, meaning they are designed to be used in situations where there is less than approximately two pounds per linear inch compression. These grooved gaskets resist compression set and are very easy to use. Aluminum can be added to these gaskets as well, which increases their shielding capacities.
Surface Mounted EMI Shielding
Surface mounted gaskets, are useful when space is limited. Surface mounted gaskets are also great for when the application of a surface mounted gasket is more economically viable.
Some surface mounted gaskets are attached to a silicone elastomeric extrusion which creates an excellent low force environmental seal. Gaskets like this usually provided shielding quality from 86 dB to 165 dB.
EMI Shield Gasket Construction
There are a few different processes used to make gaskets. The design process of a gasket will depend on what the gasket will be used for. Common processes for making EMI shield gaskets include die-cutting, digital die-less creation, and pressure sensitive adhesion. Understanding the construction methods of different gaskets can be helpful when choosing which product to purchase.
Many gaskets are made using a die-cut process. This means that a piece of rubber is stamped out and then made into a gasket. Die-cut gaskets are economical for sealing the cover of a high volume box. Die-cut gaskets can also be constructed to seal unusual shapes.
Digital Die-less Cutting
Gaskets can be constructed using a digital die-less cutting process which optimises value and minimizes waste. These gaskets can be utilized anywhere die-cut gaskets are used. This is a very economically friendly manufacturing process.
Adhesive Pressure Gaskets
Gaskets can also be made using pressure sensitive adhesives. This is the process usually used to make O-ring gaskets, framed gaskets, and other custom gaskets.
Gasket Installation Tips
The company clients purchase their gaskets from will usually help them to understand the many different installation processes. Some companies even offer onsite installation under certain circumstances. When installing gaskets, there are a few things consumers should keep in mind. Using good installation practices can increase the efficiency on an entire operation. The installation will differ depending on which type of electromagnetic interference is present. The company that a consumer chooses to work with should be able to help them follow the correct installation processes and correctly install gaskets. Proper installation is key to defending devices from the many different types of electromagnetic disturbance.
- Centering the gasket on the flange is important, and can be crucial to the success of the gasket.
- Surface finish and flatness need to be satisfactory.
- Make sure any bolts or screws are tightened adequately.
- All bolts should be tightened uniformly and from side to side around the joint.
- Tighten bolts and screws in one-third increments according to the proper patterns.
- Never use liquid or metallic anti-stick lubricating compounds on gaskets. This can cause premature failure.
Other Factors to Take Into Consideration
There are a few additional factors to keep in mind when considering which type of gasket will be needed for an operation, and what manufacturer to choose gaskets and supplies from. The environment that the gasket will be exposed to is one important aspect to consider when choosing a gasket. Chemical compatibility is another important element. Will the gasket be exposed to and solvents? If so, being sure it is constructed of chemically resistant materials is paramount. Will it be exposed to high or low temperatures? If this is the case, choosing a gasket manufactured using electronically conductive plastics would not be a good choice. Will the gasket face weathering from water or to the wind? There are certain types of gaskets designed to withstand these elements. How much radiation will the gasket be subjected to? Some gaskets do not protect from certain types or amounts of electromagnetic radiation. What processes would be necessary to switch out or fix a broken gasket? If the gasket will be placed in an area that isn't easily accessible, it would be wise to purchase one of high-quality and made with durable materials to avoid future issues. The materials available and methods of installation, as well as the gasket's manufacturing process, are all key to the success of an operation. The manufacturer that shoppers choose to purchase gaskets from should be happy to answer these and any other questions consumers may raise.
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