Educational Seminar: EMI Shielding Gasket Selection, Testing & Effective Use Part 1 of 3: Requirements for the Selection & Use of EMI Shielding Gaskets

EMI Shielding Gasket Selection, Testing & Effective Use Educational Seminar by George M. Kunkel Spira Manufacturing Corporation www.spira-emi.com

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This Educational Seminar is presented in 3 Parts: 1. Requirements for EMI Shielding Gasket Selection & Use


Addresses the importance of compatibility of the gasket and joint surfaces to ensure system performance throughout the life of the system.

2. Shielding Effectiveness Test Methods


Various Shielding Effectiveness test methods are discussed (past & present methods), and results are presented and compared.

3. Transfer Impedance Test Method & Conclusion


A cost effective option which allows for selecting the proper gasket and joint finish to meet the required shielding for the life of a system.

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This seminar is by George M. Kunkel from Spira Manufacturing Corporation. Please view the full audio/visual seminar at: www.spira-emi.com/education

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Educational Seminar: EMI Shielding Gasket Selection, Testing & Effective Use Part 1 of 3: Requirements for the Selection & Use of EMI Shielding Gaskets

Part 1 of 3:

Requirements for EMI Shielding Gasket Selection & Use 1-3

Overview of Requirements  The EMI gasket and gasketed joint surfaces should provide the required shielding level, last the life of a system, not degrade, and be cost effective.


Loss of surface conductivity of gasket and joint surfaces should not jeopardize the required shielding.




The gaskets should be able to maintain their conductivity in transportation and storage environments.




The gasket and joint surfaces should be compatible with each other in the environment in which the system will operate.




The selection of gasket and joint surfaces along with fastener spacing should be optimized for cost effectiveness.

 The EMI gasket test methods used to grade the gaskets should address the compatibility of the gasket and joint surfaces to ensure system performance throughout the life of the system. 1-4

This seminar is by George M. Kunkel from Spira Manufacturing Corporation. Please view the full audio/visual seminar at: www.spira-emi.com/education

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Educational Seminar: EMI Shielding Gasket Selection, Testing & Effective Use Part 1 of 3: Requirements for the Selection & Use of EMI Shielding Gaskets

Loss of Surface Conductivity Due to Oxidation after Moisture Soak  This Moisture Soak data illustrates the following:











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Pure 2024 Aluminum (clad/clad) shows very little loss of conductivity. The materials with a tin finish show no loss in conductivity. All of the other materials and finishes show a loss of approximately 2 orders of magnitude. This change in conductivity represents a loss of approximately 40 dB of shielding.

Results of testing extracted from “Corrosion Control in EMI Design” paper by Earl Grosshart of Boeing Aerospace Company.

Ω ) Resistance (mΩ Material Alum 2024

Finish

Initial

400 HR 95% RH

1000 HR 95% RH

1.1 5.0

30.0

clad/clad

1.3

2024

clean only/clean only

0.11

6061

clean only/clean only

0.02

7.0

13.0

2024

light chromate conversion/same

0.40

14.0

51.0

6061

light chromate conversion/same

0.55

11.5

12.0

2024

heavy chromate conversion/same

1.9

82.0

100.0

6061

heavy chromate conversion/same

0.42

3.2

5.8

cadmium/cadmium

1.8

2.8

3.0 2.5

Steel 1010

2.0

1010

cadmium-chromate/same

0.7

1.2

1010

silver/silver

0.05

1.2

1.2

1010

tin/tin

0.01

0.01

0.01

Copper

clean only/clean only

0.05

1.9

8.1

Copper

cadmium/cadmium

1.4

3.1

2.7

Copper

cadmium-chromate/same

0.02

0.4

2.0

Copper

silver/silver

0.01

0.8

1.3

Copper

tin/tin

0.01

0.01

0.01

Effects of Moisture Soak on Shielding Quality of Gasketed Joint  Shielding Quality of Tin-Lead plated EMI Gaskets using various joint surfaces before and after being subjected to 336 hours of Moisture Soak.


Nickel plated aluminum joint surfaces measured a loss in Shielding Quality of approximately 25 dB.




Chemical film plated aluminum joint surfaces measured a loss in Shielding Quality of approximately 15 dB.




Tin plated aluminum joint surfaces had no loss in Shielding Quality.

1. Tin Plated Aluminum Joint Surface 2. Chemical Film Plated Aluminum Joint Surface 3. Nickel Plated Aluminum Joint Surface

3b 2b 3a 2a

1a 1b 1-6

“Spira-Shield” Tin-Lead Plated Gaskets were used for Testing.

1G

This seminar is by George M. Kunkel from Spira Manufacturing Corporation. Please view the full audio/visual seminar at: www.spira-emi.com/education

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Educational Seminar: EMI Shielding Gasket Selection, Testing & Effective Use Part 1 of 3: Requirements for the Selection & Use of EMI Shielding Gaskets

Loss of Conductivity Due to Storage Environment  This test data illustrates a loss of conductivity of various gaskets as a result of being stored on a shelf in an office exposed to normal temperature, moisture and pressure environments.

New Aged 1 Year (stored on shelf)

 The silver filled elastomeric gasket experiences a significant loss of conductivity after 1 year.  This was caused by sulfur in the environment penetrating the elastomeric binder and coating the silver particles with a non-conductive silver sulfide.  Stainless Steel, Tin Plated, and Monel materials had less conductivity loss.

Shielding Quality (SQ) = 20 log (377/ZT) 1-7

Transfer Impedance Test Data of EMI Gaskets Against Chemical Film Plated Aluminum

Loss of Conductivity Due to Storage Environment  These Knitted Wire Mesh gaskets were exposed to a Salt Fog Environment.

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Recorded by George Roessler. Frequency Technology, March 1969.

This seminar is by George M. Kunkel from Spira Manufacturing Corporation. Please view the full audio/visual seminar at: www.spira-emi.com/education

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Educational Seminar: EMI Shielding Gasket Selection, Testing & Effective Use Part 1 of 3: Requirements for the Selection & Use of EMI Shielding Gaskets

Galvanic Corrosion  Galvanic Corrosion occurs when two incompatible metals are combined and corrosion occurs.  It can result in a loss of structural integrity as well as a significant loss of shielding.  Material Compatibility must be addressed in shielding design in order for the design to be effective over time, and is especially important if a system is to be exposed to environmental conditions.

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Material Compatibility

Extracted from SAE Standard SAE, ARP-1481

Titanium

Miscellaneous

Copper Alloys

and PH Steels

Corrosion Resistant Steel High Nickel

GASKET MATERIALS

Carbon and Alloy Steel AISI-410

Aluminum Clad, 1000 3000, 5000 6000 Series Casting 356

Aluminum 2000, 7000 Series

MATERIALS

None Mil-C-5541 Class 1A Mil-C-5541 Class 3 Electroless Nickel Cadmium Plated Bare Cadmium Colored Chromate Cadmium Clear Chromate Chromium Mil-C-5541 Class 1A Mil-C-5541 Class 3 Electroless Nickel Cadmium Bare Cadmium Colored Chromate Cadmium Clear Chromate Chromium Tin Cadmium Bare Cadmium Colored Chromate Cadmium Clear Chromate Nickel Electroless Nickel Chromium Tin Lead Silver Passivated Cadmium (Passivated) Tin Passivated Cadmium (Passivated) Tin Tin Silver Gold Solder (Lead-Tin) Silver Paint Zinc Paint Silver Adhesive Carbon Adhesive None Nickel

FINISHES

Aluminum Tin Plated Monel Silverelastomer Stainless Steel Beryllium Copper

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A A C E C C

A A D C C C

A A D C C C

D D A D A D

A A D C C C

A A D C A C

A A D C A C

A A A A A D

A A D C D C

A A D C C C

D D A D A D

D A D E D C

A A D C A C

A A D C A C

A - Compatible D - Compatible in controlled temperature and humidity only.

A A A A A D

A A D A A C

A A D C C C

A A D C A C

A A D C A D

D D A D A D

D D A D A D

A A A A A C

A A A A A C

D A D X D D

X A A A A D

C A A D A C

A A D E D C

A A A D A D

C A A D A C

A A D E D C

A A A D A C

A A A D A C

X A D A A C

X A D A A C

A A A D A C

X D D A A D

X A D X X C

D D D A A C

D D D A D C

D D A D A C

D D A D A C

C - Requires sealing if exposed to humid environment. E - Requires sealing regardless of exposure. X - Not usable.

This seminar is by George M. Kunkel from Spira Manufacturing Corporation. Please view the full audio/visual seminar at: www.spira-emi.com/education

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Educational Seminar: EMI Shielding Gasket Selection, Testing & Effective Use Part 1 of 3: Requirements for the Selection & Use of EMI Shielding Gaskets

Galvanic Corrosion of Mesh Gasket  Rockwell International found corrosion by a Tin Plated Mesh Gasket against an Aluminum MCGS Frame after the system was exposed to 6 months of field environmental conditions.


Although the gasket met the material compatibility “tin plating” requirements, the tin plating was thin and porous which allowed the iron from the structural wire to migrate through the plating.




The gasket that met the requirements of their 336 hour salt fog test was an “Edge-plated (tin) Spira-Shield” gasket.

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Corrosion of EMI/RFI Wire Mesh Gaskets  This graphic shows the performance of various mesh gaskets against Aluminum surface after 240 hours of salt fog exposure. By George Roessler of Tecknit, Frequency Technology, March 1969.

Aluminum Plate No Finish

Aluminum Plate Chromate Finish

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This seminar is by George M. Kunkel from Spira Manufacturing Corporation. Please view the full audio/visual seminar at: www.spira-emi.com/education

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Educational Seminar: EMI Shielding Gasket Selection, Testing & Effective Use Part 1 of 3: Requirements for the Selection & Use of EMI Shielding Gaskets

Corrosion of EMI/RFI Wire Mesh Gaskets  This graphic shows the performance of various mesh gaskets against a Steel surface after 240 hours of salt fog exposure. By George Roessler of Tecknit, Frequency Technology, March 1969.

Steel Plate Cadmium Finish

Steel Plate Chromate/ Cadmium Finish

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Cost Effective Shielding Design  The proper selection of an EMI gasket and compression force can easily pay for the cost of a better EMI gasket and design by minimizing the number of required fasteners.  In this maintenance cover example, View A-A illustrates how the gasket is compressed and creates a force on the cover causing the cover to bow.  Optimal fastener spacing is as wide as possible while still providing sufficient force on the gasket half way between fasteners. 1-14

This seminar is by George M. Kunkel from Spira Manufacturing Corporation. Please view the full audio/visual seminar at: www.spira-emi.com/education

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Educational Seminar: EMI Shielding Gasket Selection, Testing & Effective Use Part 1 of 3: Requirements for the Selection & Use of EMI Shielding Gaskets

Cost Effective Screw Spacing Design  The graphs illustrate fastener spacing as a function of force to compress a gasket, the height of the gasket, and the thickness of the cover plate.  The 2nd graph illustrates doubling the height of the gasket and thickness of the cover allows for doubling of the screw spacing and reduction in the number of fasteners.

Height of gasket and cover thickness = .063”

 Using a lower force gasket can significantly reduce the required number of fasteners. 1-15

Height of gasket and cover thickness = .125”

Requirements Conclusion  Here’s a valuable quote from “Corrosion and the EMI/RFI Knitted Wire Mesh Gasket” by George D. Roessler of Technit, from Frequency Technology, March 1969.  “If the possibility of corrosion is neglected in the design phase, shielding might as well be a second thought. Since shielding is of utmost importance in our crowded electronic spectrum, corrosion must be considered at all times. Malfunction of equipment due to electromagnetic interference can not be tolerated in this technological day and age.”  Therefore, Material Compatibility, along with a cost-effective design, becomes even more important each year as we continue advancing in technology… 1-16

This seminar is by George M. Kunkel from Spira Manufacturing Corporation. Please view the full audio/visual seminar at: www.spira-emi.com/education

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Educational Seminar: EMI Shielding Gasket Selection, Testing & Effective Use Part 1 of 3: Requirements for the Selection & Use of EMI Shielding Gaskets

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Contact Us with Questions or Sample Requests: www.spira-emi.com [email protected] (818) 764-8222 1-17

This seminar is by George M. Kunkel from Spira Manufacturing Corporation. Please view the full audio/visual seminar at: www.spira-emi.com/education

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