How to choose the right EMC shielding gasket?

Correctly choosing an EMC shielding gasket is mandatory to ensure the performance and the longevity of an electrical device. Doing the wrong choice, is compromising the global electromagnetic compatibility (EMC) of the whole system.
Be smart, follow the guide!

Foam Gasket for EMI - Joint silicone CEM EMI - COMPELMA

Why use an EMC and/or IP gasket in an electrical assembly?

The first objective is to ensure sealing:
• To particles(dust)
• And/or fluids(air, water)
• And/or electronic (mass recovery) in the case of  EMC shielding gaskets ( electromagnetic compatibility )

This water resistance is assured between two moving parts of a piece of equipment. For example, between two parts of an assembled electronic box, between a closet door and its frame, or around the periphery of the cover of a piece of equipment.

Sealing against fluids and particles - IP index

The level of sealing against water and dust of an electronic equipment is given by its IP rating (Ingress Protection). This protection rating is standardised by the International Electrotechnical Commission.

It consists of the letters IP followed by two numbers(or a letter in certain specific cases).The first number indicates protection against solids(particles and dust).The second number indicates the protection against liquids. To comply with the rules, the tests must be done with water.

For example, an IP68 certified equipment is completely dust proof and waterproof to a specific depth and time duration specified by the manufacturer.

For more information, you can consult the Wikipedia page on the subject.

Now, let's get down to business!

Electromagnetic sealing - Grounding

In addition to fluid proofing, the gaskets can be made of an electrically conductive material to provide an electromagnetic shielding through grounding. What is electromagnetic shielding and electromagnetic compatibility (EMC)?

Many fabrication methods make it possible to manufacture conductive gaskets:
- Using a metal particle charged silicone (Nickel and Carbon [Ni/C] or Silver and Aluminium[Ag/Al])
- Drown a metal mesh in silicone (Monel or aluminium type)
- Surround the joint with a conductive material (for example metallized fabric [Ni/Cu/Ni], therefore conductive)

These different methods of gasket manufacturing ensure a shielding level up to 120dB for  EM(electromagnetic) and RF (radio frequency).

Integration of EMC and IP gaskets in an electronic assembly

To achieve high performance levels, the gaskets must be properly integrated into the electronic design. This integration must be considered at the beginning of the project.

For example, to ensure IP68 sealing and ground continuity around an electronic enclosure’s periphery: a groove must be designed to integrate the gasket. Without this groove, an IP68 level is difficult to achieve.

Several solutions exist to compensate for the detection of leaks in a piece of equipment after its conception. However, these methods are still not optimized and so not recommended. Indeed, the performance levels can only be lower.

For example: Foam gaskets surrounded by a conductive fabric allow grounding on openings or at certain locations of a piece of equipment (around a connector for example). These gaskets are placed directly on the metallic surface and are held in place by an adhesive. A groove is therefore not necessary. However, there must be enough space in the design.

If a high IP sealing is required, conductive foam gaskets are not suitable. The conductive fabric around the polyurethane foam stops dust particles and some droplets, but shows its limits in a more demanding environment.

Beware of compressive forces

In addition to the expected level of sealing, special attention must be paid to the compression forces in the electronic assembly. If the EMC shielding gasket is too hard or oversized, your assembly may be degraded by unexpected mechanical stresses. On the other hand, if the conductive gasket is too soft, too compressed or undersized, it may degrade rapidly (deformation or even tearing) and the EMC and/or IP tightness will no longer be guaranteed.

A few examples of EMI shielding gaskets:

EMC foam shielding gaskets with conductive fabric:
Foam Gasket for EMI - Joint silicone CEM EMI - COMPELMA

These EMC foam gaskets require low compression forces (due to the polyurethane foam). They can therefore be used in lengths of several meters without too much mechanical stress. These EMC shielding gaskets also have good mechanical resilience and withstand abrasion and compression/decompression cycles. They are therefore suitable for RFID cabinet door openings, for example.

EMC shielding gasket made of conductivesilicone (Ni/C or Ag/Al charged):
bi material gasket - joints bi matière - silicone conducteur - fluorosilicone - EMI and IP sealing - Compelma

The metallic particles in the silicone make it harder than a neutral silicone. Therefore an EMC shielding gasket made of charged silicone will be hard (hardness > 60 Shore A). The design of the assembly and the compression forces will have to be adjusted accordingly. For example by increasing the number of clamping screws along the gasket. Bi-material EMC silicone gaskets are an excellent alternative for reducing the required compression forces.

EMC shielding metallic gaskets:
Metallic Gasket for EMI - Joint métallique CEM EMI - COMPELMA

These metal gaskets for EMC shielding are made from a 0.15mm thick metal sheet (Sandvik Chromflex). The spring teeth protrude from the gasket by 0.5mm. This gives an overall gasket height of 0.2mm and 0.15mm in maximum compression. The compression force for this type of gasket is minimal.The teeth are easily compressible.

To avoid the risk of over-compression of EMC shielding gaskets you need to be able to control the compression of the EMC gaskets. Either by controlling the tightening torque or by adding mechanical stops.

Choice of materials for EMI shielding gaskets

The choice of materials must be taken into account when selecting the type of shielding gasket. Not only for electrical conductivity and EMC shielding performance, but also for compatibility with its environment. Galvanic couples are important to ensure the longevity of an equipment. Some metals, in a salty environment, will react with each other and oxidize rapidly.

For example, Ni/C (Nickel Graphite) loaded EMC gaskets are recommended when mounted on a nickel surface (plated or painted) enclosure. On the other hand, a silver or copper loaded gasket in contact with an aluminium housing in a salty environment will corrode quickly. This will result in mechanical degradation of the seal, with a loss of EMC and/or IP sealing. In addition to corrosion on the worst case.

Galvanic Couples - EMC/EMI - Compelma - Nickel Carbone - Ag Al

Grounding with the EMC shielding gasket

To be functional, the EMC gasket must be grounded.This grounding must be done directly against the metal. Some coatings or paints are electrically insulating. In this case, it is important to ensure that the grounding is made by partially removing the paint or the surface coating, which allows a contact of conductive surface against conductive surface.

Some surface coatings are conductive. For example for aluminium surface coatings (on a heat sink for example), Surtec 650 is electrically conductive, as opposed to anodizing which is insulating.

Lifetime of an EMC shielding gasket and maintenance

The shielding effectiveness of an EMC gasket in place varies very little over time (except in the case of oxidation or non-compliance with galvanic couples). However, if maintenance is carried out on the equipment and the EMC gasket is removed, you must be careful.

During a disassembly operation, the gasket may come out of its groove or move. In this case, depending on its level of resilience (its ability to return to its original shape), the electromagnetic shielding and IP sealing may be impacted.

We recommend changing EMC gaskets (especially loaded silicone or foam and conductive fabric versions) at each maintenance operation to avoid a second maintenance operation after reassembly of the equipment and the detection of an EMC or fluid leak due to the gasket

Friction resistance is also a consideration in some applications. EMC foam gaskets with conductive fabric are particularly resistant to friction and wear. These conductive gaskets are therefore suitable for electromagnetic (EMC) and radio frequency (RF) sealing of cabinet doors or between two metallic parts

In all cases, and for all types of gaskets, we recommend a regular inspection of the equipment and gaskets and a replacement if necessary. It is better to replace a gasket than to have to carry out maintenance following a system failure.

What does the shielding effectiveness of an EMC shielding gasket depend on?

The level of shielding does not only depend on the chosen materials. Performance is all about finding the best balance between integration, price, maintenance and material compatibility. Let us help you choose your EMC gaskets to ensure a high level of electromagnetic shielding (EMC) and/or IP sealing performance.

To help you understand this, we have listed the characteristics of the different types of EMC shielding gaskets available. You will notice that no solution is perfect. Before making your choice, contact us to validate the EMC shielding technology.

You can also contact us now via the chat or the contact form at the bottom of the page. 😃

Charged silicone gaskets:

These are elastomeric (silicone) gaskets. Silicone can be charged with metal particles to make it conductive and thus provide electromagnetic shielding through its electrical conductivity. A charged silicone is harder than a neutral silicone (about 65 Shore A for a conductive silicone against 40 for a neutral silicone). A silicone type fluorosilicone can also be used to ensure a better resistance to solvents and hydrocarbons overtime.

Material of the EMI gasket

Loaded silicone (Ni/C or Ag/Al) and/or neutral silicone. Fluorosilicone variant for demanding applications (e.g. medical or military applications).

Forming processes of the EMI gasket

Silicone gaskets for EMC and/or IP can be manufactured by extrusion to a standard or custom profile (expect to pay few hundreds euros for a custom extrusion profile with a lifetime guarantee). Extruded EMC and/or IP silicone gaskets can be supplied by the linear meter or cut to length.

These gaskets can also be cut from a conductive silicone sheet to obtain a flat gasket.

Variant 1: Bi-material EMC shielding gaskets (neutral and loaded silicone)
bi material gasket - joints bi matière - silicone conducteur - fluorosilicone - EMI and IP sealing - Compelma

Bi-material silicone EMC (EMI) shielding gaskets can be made by extruding two types of silicone simultaneously: a loaded silicone(Al/Ag or Ni/C) and a neutral silicone (fluorosilicone or not). The advantage is the flexibility of the EMC shielding gasket compared to a pure loaded silicone gasket (harder). The arrangement of the two types of silicone on the gasket profile is variable depending on the specifications to be achieved. More information on these bi-material EMC gaskets can be found on the bi-material gaskets product page.

Variant 2: Neutral silicone EMC shielding gaskets
Silicone Gasket for EMI - Joint silicone CEM EMI - COMPELMA

For certain demanding projects (nuclear, military or medical), neutral silicone gaskets are used. The advantage is that the flexibility of neutral silicone is retained and the electrical conductivity of the metal is added by the metal screening. The metal screening is molded in the silicone during manufacture (usually Monel or aluminium). This type of gasket has excellent resilience and durability. It is only manufactured by molding or plate cutting.

Sealing level of the EMI gasket

These gaskets (conductive and non-conductive) achieve very high levels of fluid and particle tightness (up to IP68 or IP69). The highest fluid tightness levels are achieved when the gaskets are placed in a groove.

We can help you choose the dimensions of the gasket (in profile and length) according to the design of your groove, or vice versa.

Compelma opinion

These EMC gaskets are an excellent solution in terms of compromise between performance, cost and durability. We have a good margin of manoeuvre on the shaping and design of this type of gasket. This makes them very good candidates for most electronic projects.

EMI shielding metallic gaskets :

Metallic Gasket for EMI - Joint métallique CEM EMI - COMPELMA

Metallic EMC shielding gaskets are manufactured by chemical cutting and mechanical forming from 0.15mm thick steel plate (Sandvik Chromflex). These shielding gaskets have a series of small spring teeth around the periphery. This allows them to compensate for gaps due to tolerances between two metal castings for example.

Material of the EMC gasket

Sandvik Chromflex metal foil, 0.15mm thick.

Forming processes of the EMI gasket

You provide a 3D drawing of the contours of the EMC shielding gaskets. On this basis we make a proposal for the positioning of the spring teeth along the joint. Prototype production is carried out using prototype tooling (soft tooling). A mass production tool is then required for higher volume production. These shielding gaskets are only custom made.

Sealing level of the EMI gasket

These types of EMC shielding gaskets are, by definition, only designed for EMC shielding by providing grounding between two foundries. There is almost no sealing against particles (IP)

Compelma opinion

These shielding gaskets are widely used in microwave gaskets. In particular by large industrial companies in the telecoms, military and medical sectors. The launch costs imposed by the nature of the EMC gasket are more easily amortized on volumes of several tens of pieces minimum.

EMC shielding foam gaskets with conductive fabric

Foam Gasket for EMI - Joint silicone CEM EMI - COMPELMA

These EMC shielding gaskets are economical and easily applicable in most electronic projects. Conductivity is ensured all around the gasket by the conductive fabric. The metallization (Ni/Cu/Ni) applied to the polyester fabric guarantees a very good abrasion resistance (in the case of EMC shielding on a door opening for example). The polyurethane foam body ensures good a mechanical behavior and resilience.

Material of the EMC gasket and forming processes

Nickel-Copper-Nickel metallised polyester fabric thermo formed around a polyurethane foam profile (unloaded). An adhesive can be added (electrically conductive or not).

Sealing level of the EMI gasket

These EMC shielding foam gaskets ensure a good level of EMC shielding. The foam structure and the fabric block particles and dust. Fluid tightness is very limited.

Compelma opinion

Thanks to its strong capacity to regain its initial shape, this type of gasket can ensure several thousand compression and decompression cycles (corresponding to the opening and closing cycles of an RFID cabinet door for example).

The wide range of profiles and sizes make it easy to do EMC shielding for the vast majority of projects. These EMC shielding gaskets can be cut to length to suit the application.

Although it is not advisable to do so, these gaskets are often used as a last resort for electromagnetic leakage detected too late in the design.

Other EMC gasket technologies: EMC contact strips and EPDM gaskets with metal mesh

These two types of EMC shielding products are still available on several electronic distributors' websites. However, these EMC products are obsolete, you can get much better results with other products for the same price and with better durability.

For example, copper or stainless steel EMC shielding contact bars do not hold up well to repeated compression cycles. Some of the teeth may break due to wear and tear, which has a significant impact on the life of the product. These EMC shielding contact strips are also permeable to dust and are very sensitive to oxidation (especially on the copper versions). EPDM EMC shielding gaskets with a metal mesh look homemade compared to loaded silicone gaskets (bi-material or standard). The cost is also more competitive with loaded silicone EMC shielding gaskets.

Limitations of EMC shielding gaskets

The gaskets we have discussed are designed for EMC shielding in the microwave range (metallic gaskets), RFID (foam gaskets with a conductive fabric) or Radio Frequency more generally. However, these seals are not suitable for low frequency electromagnetic shielding (10kHz - H field). Indeed,these magnetic fields are only stopped by gaskets with a high ferrous load(iron). Indeed the shielding joint must be magnetic to control and/or direct the magnetic fields. Mu-metal (μ-metal), an alloy of iron and nickel, is used in particular for projects with magnetic fields. At Compelma we do not propose this material or gaskets for magnetic shielding.

How to choose a shielding gasket for your EMC?

A complete article on EMC shielding gaskets that can be summarized in one sentence:

Get professional advice and support.
He will be able to share with you his experience on the choice of materials and applications.

Each EMC gasket application is too specific to provide a generic solution. The type of application, the integration stage, the environment, the sector, the technical requirements. These are all parameters that a professional can help you to understand.

Supporting you at the earliest stage of your conception also allows you to approach the tests and certifications with confidence. By having confidence in the materials you have chosen and their level of performance.  For example,avoiding silicon-based materials in space or medical applications (because of the risk of out-gassing) or mixing galvanic couples in a saline environment.

Why choose Compelma?

Logo COMPELMA - EMI and Thermal management - CEM et management Thermique

More than 80% of our products are custom developed using technologies and processes that we master. Our aim is always to offer the most suitable EMC shielding parts within the budget.

With more than 30 years of experience and advice, we are happy to support you. For new projects, or in the search for alternatives or obsolescence.

Gore GS2100, an example of an alternative to obsolescence

The GS2100 material has been placed in obsolescence by the manufacturer Gore. However, this material was qualified on many military projects, still deployed, on which maintenance is necessary.
Compelma was asked by its customers to propose an alternative material, with the same technical characteristics, that could replace GS2100. After consultations and exchanges with our suppliers and partners, we developed the alternative material: CO-ECE2110.
This Compelma material has since been qualified on the projects concerned and is supplied regularly.

Do you have any questions or simply want to know more about EMI shielding gaskets?

You can contact us (Florian, Li or Clément) using the tchat for a live answer, or via the contact form below.

Thank you for reading this long article to the end, see you soon! ⚡
Clément for Compelma

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