This technical information has been contributed by
Tech-Etch Inc.

Click here to find suppliers

EMI/RFI Shielding Types

EMI/RFI Shielding Types - Shielding Strips

Shielding strips are designed for a wide variety of application requirements. They are available in strips ranging from 16 to 24 inches in length, in continuous coils up to 35 feet long, as single fingers, or cut to requested full-finger lengths. Special modifications can be made to suit your requirements.

Uncompressed heights of standard finger stock range from .03" to .44", which will occupy gaps as low as .01". Many gaskets are offered in two material thicknesses to meet diverse application compression requirements: "Standard" and "TF", which requires less force to compress the gasket to its operating range.

Beryllium Copper Products

  • Finger Stock
  • "D" Connector Gaskets
  • Contact Rings

Stainless Steel Products

  • Finger Stock
  • "D" Connector Gaskets
  • Expansion Slot

Custom Designed Shielding

  • Many custom designed shielding components can be supplied for special applications from high volume requirements using progressive dies, to prototype and small quantities utilizing photoetch fabrication.
EMI Shielding Performance
Material H-Field - 100kHz E-Field - 10MHz P-Field - 1GHz
BeCu >110 dB >110 dB <110 dB
Note: Plating the mating surfaces with the same material will provide superior performance. Chromate chemical film on aluminum maintains surface conductivity by reducing corrosion.

Shielding Compatibility

Electromagnetic Compatibility
EMI/RFI Shielding Products are designed to either keep out or keep in electromagnetic interference. Shielding reflects and absorbs incident radiation. The higher the attenuation of the shielding, the more effective it is at keeping in or out the undesired electromagnetic interference.

Electrochemical Compatibility
To avoid galvanic action between contacting metals refer to this chart. Materials in adjacent groups may be safely used together. Choosing materials from within a single group in the table will provide the least corrosion due to galvanic action when the materials are in contact for an extended period of time with appropriate protective finish.

Grouping of Metals by Decreasing Galvanic Activity
Group 1 Group 2 Group 3 Group 4
Magnesium
Magnesium Alloys
Aluminum
Aluminum Alloys
Zinc & Zinc Plating
Chromium Plating
Aluminum
Aluminum Alloys
Zinc & Zinc Plating
Chromium Plating
Cadmium Plating
Carbon Steel
Iron
Nickel & Nickel Plating
Tin & Tin Plating
Tin/Lead Solder
Cadmium Plating
Carbon Steel
Iron
Nickel & Nickel Plating
Tin & Tin Plating
Tin/Lead Solder
Brass
Stainless Steel
Beryllium Copper
Copper & Copper Alloys
Nickel/Copper Alloys
Monel
Brass
Stainless Steel
Beryllium Copper
Copper & Copper Alloys
Nickel/Copper Alloys
Monel
Silver

Attenuation

For maximum attenuation of a gasketed gap, the contact resistance of the mounting joint and closing joint must be very low and remain so throughout the life of the product. While a gasket may have the potential for very high attenuation under ideal conditions, over time oxidation, corrosion and dirt at the mounting and closing joints may reduce effectiveness. Factors influencing contact resistance over the life of the product are pressure (closing force), plating, and wiping action. Your supplier's engineers can help you determine the optimal specifications to ensure sustained attenuation.

Compression

The purpose of shielding is to occupy and thereby shield the gap that exists between two adjoining surfaces. In order to be effective, shielding gaskets must be able to occupy both the maximum and minimum gaps, which exist due to fabrication tolerances, misalignment of surfaces, or irregular surfaces. Proper compression management is essential to ensure effective EMI shielding.

EMI RFI Shielding

  • At the maximum gap the gasket should be compressed approximately 25%.
  • Gaskets may be compressed to 50% of their height or more.

EMI RFI Shielding


Materials

Beryllium Copper
Beryllium Copper (BeCu) is a high performance metal which can be fabricated into a wide variety of components. Its mechanical and electrical properties make it the ideal material for EMI/RFI shielding products.

Unique Material Properties
Beryllium copper's electrical properties provide shielding effectiveness over an extremely broad frequency range. At the same time, its mechanical properties yield a high deflection range, in addition to a long life without compression set. BeCu finger stock provides maximum spring properties for strength and fatigue resistance, plus excellent conductivity. Available in many plating options, BeCu has a high cycle time and conforms to large gap variations making it the best material for attenuation.

Material Specifications

Chemical Composition
Beryllium: 1.80-2.00%
Cobalt plus nickel: 0.20% Min.
Cobalt + nickel + iron: 0.6% Max.
Copper: Balance

Physical Properties (heat treated)
Electrical conductivity (% IACS): 22-25
Modulus of elasticity (psi): 18.5 x 106

Mechanical Properties (heat treated)
Temper (1,000 psi) 1/4 HT 1/2 HT
Tensile strength: 175 Min. 185 Min.
Yield strength .2% offset: 150 Min. 160 Min

Stainless Steel
Stainless steel is an economical alternative to beryllium copper for shielding applications where high attenuation is not required. It does not have the electrical conductivity of BeCu and is stiffer. Mechanical considerations generally limit the use of stainless steel to low profile strips and twisted contacts. Items are identified by SS in the notes.

Material Specifications
Type 301 Stainless steel possesses good heat and corrosion resistance.

AISI 301 Analysis
C: .15 Max.
Mn: 2.00 Max.
Si: .750 Max.
P: .040 Max.
S: .030 Max.
Cr: 16.00/18.00
Ni: 6.00/8.00

This technical information has been contributed by
Tech-Etch Inc.

Click here to find suppliers

Home |  About Us |  Back To Technical Library |  Contact Us
Copyright © 1996-2017 JobShop.com. All Rights Reserved.
General or Technical Questions? E-mail support@JobShop.com