EMI Shielding Gasket Selection, Testing & Effective · PDF file2 Educational Seminar: EMI Shielding Gasket Selection, Testing & Effective Use Part 1 of 3: Requirements for the Selection

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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

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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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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Part 1 of 3:

Requirements for EMI Shielding Gasket

Selection & Use

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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.

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Initial400 HR

95% RH

1000 HR

95% RH

Alum 2024 clad/clad 1.3 1.1 2.0

2024 clean only/clean only 0.11 5.0 30.0


2024 light chromate conversion/same 0.40 14.0 51.0


2024 heavy chromate conversion/same 1.9 82.0 100.0


Steel 1010 cadmium/cadmium 1.8 2.8 3.0

1010 cadmium-chromate/same 0.7 1.2 2.5

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

Resistance (mΩΩΩΩ )FinishMaterial

Initial400 HR

95% RH

1000 HR

95% RH

Alum 2024 clad/clad 1.3 1.1 2.0









1010 silver/silver 0.05 1.2 1.2

1010 tin/tin 0.01 0.01 0.01







Initial400 HR

95% RH

1000 HR

95% RH

Alum 2024 clad/clad 1.3 1.1 2.0









1010 silver/silver 0.05 1.2 1.2

1010 tin/tin 0.01 0.01 0.01







Loss of Surface Conductivity Due to Oxidation after Moisture Soak

Results of testing extracted

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

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.

This Moisture Soak data illustrates the following:

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1. Tin Plated Aluminum Joint Surface

2. Chemical Film Plated Aluminum Joint Surface

3. Nickel Plated Aluminum Joint Surface

1. Tin Plated Aluminum Joint Surface

2. Chemical Film Plated Aluminum Joint Surface

3. Nickel Plated Aluminum Joint Surface

1a

1b

3a

3b

2a

2b

Effects of Moisture Soak on Shielding Quality of Gasketed Joint

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.

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

1a

1b

3a

3b

2a

2b

“Spira-Shield” Tin-Lead Plated Gaskets were used for Testing. 1G

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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.

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.

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

Shielding Quality (SQ) = 20 log (377/ZT)

NewAged 1 Year(stored on shelf)

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These Knitted Wire Mesh gaskets were exposed to a Salt Fog Environment.

Recorded by George Roessler. Frequency Technology, March 1969.

Loss of Conductivity Due to Storage Environment

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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

A - CompatibleD - Compatible in controlled temperature

and humidity only.

MATERIALS

GASKET

MATERIALS

Alu

min

um

Cla

d, 100

0

3000, 5000

Corr

osio

n

Resis

tant

Ste

el

Hig

h N

ickel

FINISHES

None

Mil-C

-5541

Cla

ss 1

A

Mil-C

-5541

Cla

ss 3

Ele

ctrole

ss N

ickel

Cadm

ium

Pla

ted B

are

Cadm

ium

Co

lore

d C

hro

ma

te

Cadm

ium

Cle

ar C

hro

mate

Chro

miu

m

Mil-C

-5541

Cla

ss 1

A

Mil-C

-5541

Cla

ss 3

Ele

ctrole

ss N

ickel

Cadm

ium

Bare

Cadm

ium

Co

lore

d C

hro

ma

te

Cadm

ium

Cle

ar C

hro

mate

Chro

miu

m

Tin

Cadm

ium

Bare

Cadm

ium

Co

lore

d C

hro

ma

te

Cadm

ium

Cle

ar C

hro

mate

Nic

kel

Ele

ctrole

ss N

ickel

Chro

miu

m

Tin

Le

ad

Silver

Passiv

ate

d

Cadm

ium

(P

assiv

ate

d)

Tin

Passiv

ate

d

Cadm

ium

(P

assiv

ate

d)

Tin

Tin

Silver

Gold

Sold

er (L

ead-T

in)

Silver P

ain

t

Zin

c P

ain

t

Silver A

dh

esiv

e

Carb

on A

dhe

siv

e

None

Nic

kel

Aluminum A A A D A A A A A A D D A A A A A A A D D A A D X C A A C A A A X X A X X D D D D

Tin Plated A A A D A A A A A A D A A A A A A A A D D A A A A A A A A A A A A A A D A D D D D

Monel C D D A D D D A D D A D D D A D D D D A A A A D A A D A A D A A D D A D D D D A A

Silverelastomer E C C D C C C A C C D E C C A A C C C D D A A X A D E D D E D D A A D A X A A D D

Stainless Steel C C C A C A A A D C A D A A A A C A A A A A A D A A D A A D A A A A A A X A D A A

Beryllium Copper C C C D C C C D C C D C C C D C C C D D D C C D D C C D C C C C C C C D C C C C C

Mis

cellan

eous

Titaniu

m

60

00 S

eri

es

Casting 3

56

Alu

min

um

20

00,

70

00 S

eri

es

Carb

on

and

Allo

y S

tee

l

AIS

I-41

0

an

d P

H S

teels

Coppe

r A

lloys

C - Requires sealing if exposed to humid environment.

E - Requires sealing regardless of exposure.

X - Not usable.

MATERIALS

GASKET

MATERIALS

Alu

min

um

Cla

d, 100

0

3000, 5000

Corr

osio

n

Resis

tant

Ste

el

Hig

h N

ickel

FINISHES

None

Mil-C

-5541

Cla

ss 1

A

Mil-C

-5541

Cla

ss 3

Ele

ctrole

ss N

ickel

Cadm

ium

Pla

ted B

are

Cadm

ium

Co

lore

d C

hro

ma

te

Cadm

ium

Cle

ar C

hro

mate

Chro

miu

m

Mil-C

-5541

Cla

ss 1

A

Mil-C

-5541

Cla

ss 3

Ele

ctrole

ss N

ickel

Cadm

ium

Bare

Cadm

ium

Co

lore

d C

hro

ma

te

Cadm

ium

Cle

ar C

hro

mate

Chro

miu

m

Tin

Cadm

ium

Bare

Cadm

ium

Co

lore

d C

hro

ma

te

Cadm

ium

Cle

ar C

hro

mate

Nic

kel

Ele

ctrole

ss N

ickel

Chro

miu

m

Tin

Le

ad

Silver

Passiv

ate

d

Cadm

ium

(P

assiv

ate

d)

Tin

Passiv

ate

d

Cadm

ium

(P

assiv

ate

d)

Tin

Tin

Silver

Gold

Sold

er (L

ead-T

in)

Silver P

ain

t

Zin

c P

ain

t

Silver A

dh

esiv

e

Carb

on A

dhe

siv

e

None

Nic

kel







Coppe

r A

lloys

Mis

cellan

eous

Titaniu

m

60

00 S

eri

es

Casting 3

56

Alu

min

um

20

00,

70

00 S

eri

es

Carb

on

and

Allo

y S

tee

l

AIS

I-41

0

an

d P

H S

teels

MATERIALS

GASKET

MATERIALS

Alu

min

um

Cla

d, 100

0

3000, 5000

Corr

osio

n

Resis

tant

Ste

el

Hig

h N

ickel

FINISHES

None

Mil-C

-5541

Cla

ss 1

A

Mil-C

-5541

Cla

ss 3

Ele

ctrole

ss N

ickel

Cadm

ium

Pla

ted B

are

Cadm

ium

Co

lore

d C

hro

ma

te

Cadm

ium

Cle

ar C

hro

mate

Chro

miu

m

Mil-C

-5541

Cla

ss 1

A

Mil-C

-5541

Cla

ss 3

Ele

ctrole

ss N

ickel

Cadm

ium

Bare

Cadm

ium

Co

lore

d C

hro

ma

te

Cadm

ium

Cle

ar C

hro

mate

Chro

miu

m

Tin

Cadm

ium

Bare

Cadm

ium

Co

lore

d C

hro

ma

te

Cadm

ium

Cle

ar C

hro

mate

Nic

kel

Ele

ctrole

ss N

ickel

Chro

miu

m

Tin

Le

ad

Silver

Passiv

ate

d

Cadm

ium

(P

assiv

ate

d)

Tin

Passiv

ate

d

Cadm

ium

(P

assiv

ate

d)

Tin

Tin

Silver

Gold

Sold

er (L

ead-T

in)

Silver P

ain

t

Zin

c P

ain

t

Silver A

dh

esiv

e

Carb

on A

dhe

siv

e

None

Nic

kel







Coppe

r A

lloys

Mis

cellan

eous

Titaniu

m

60

00 S

eri

es

Casting 3

56

Alu

min

um

20

00,

70

00 S

eri

es

Carb

on

and

Allo

y S

tee

l

AIS

I-41

0

an

d P

H S

teels

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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

Aluminum PlateNo Finish

Aluminum PlateChromate Finish

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.

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Steel PlateCadmium Finish

Steel PlateChromate/

Cadmium Finish

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.

Corrosion of EMI/RFI Wire Mesh Gaskets

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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.

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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.

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

Height of gasket and cover thickness = .063”

Height of gasket and cover thickness = .125”

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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…

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Thank you for watching this Educational Seminar!

Please continue with the 2nd presentation (or other) from the list below.

Contact Us with Questions or Sample Requests:

www.spira-emi.com

[email protected]

(818) 764-8222

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EMI Shielding Gasket Selection, Testing & Effective · PDF file2 Educational Seminar: EMI Shielding Gasket Selection, Testing & Effective Use Part 1 of 3: Requirements for the Selection