Critical flex and rigid-flex circuit applications often must pass very stringent electromagnetic (EM) or radio frequency (RF) interference requirements. This type of interference, if absorbed or emitted, can negatively impact the functionality and reliability of the end product when in use. To prevent this from occurring, the circuit design must incorporate shielding to eliminate either the absorption or transmission of EM or RF interference. For flex and rigid-flex PCB designs, there are two types of shielding solutions that can be applied, but which is best suited will depend upon other design requirements. In this webinar, we review shielding methods and how to implement them in a flex or rigid-flex PCB design to ensure interference free operation of your design. For more information on our custom flex and rigid-flex circuit solutions, visit https://www.epectec.com/flex.

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EMI Shielding Methods for Flex &
Rigid-Flex PCB Designs
08.27.2021

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Agenda
 EMI Overview
 Shielding Methods for Flex & Rigid-Flex Designs
– Available options:
• Copper Layers
• Silver Epoxy Ink
• Shielding Film
 Pros & Cons
 Gerber Design Requirements

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Introduction

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Introduction
 EMI definition:
– A disturbance generated by an electrical source that affects an electrical
circuit by electromagnetic induction, electrostatic coupling, or conduction.
 Negative impact of EMI:
– May degrade the performance of a circuit or even stop it from functioning.
– Effects can range from an increase in error rate to a total loss of data.
 Why shield at the circuit level?
– Reduces overall costs when shielded closest to the sensitive circuits.

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Shielding Methods

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Shielding Methods – Copper Layers
 Construction:
– Additional copper layers added external of signals.
– Same solution as used in rigid PCB designs.
– Solid plane (preferred) or cross hatched plane layers.
 Required solution for controlled impedance.
 Interconnects to ground circuit through via holes.
 Stitched vias possible but will degrade flexibility.
– Vias in flex area not recommended by IPC 2223.

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Shielding Methods – Copper Layers (continued)

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Shielding Methods – Silver Epoxy Ink
 Construction:
– Layer of silver ink added external of the flex area primary coverlay and
encapsulated with secondary coverlay.
 Connects to ground through selective coverlay openings in primary coverlay
and is encapsulated by secondary coverlay.
 Added costs due to many added process steps and additional materials.
– E.g.: silk screening/baking/2nd coverlay (repeat for 2-sided shielding).
 Old school technology.

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Shielding Methods – Silver Epoxy Ink (continued)

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Shielding Methods – Shielding Film
 Specialized film laminated to external
coverlays.
 3-layer construction:
– Electrically conductive adhesive/metallic
deposition layer/insulation layer.
 Shield connects to ground through
selective coverlay openings in primary
coverlay and is encapsulated by
secondary coverlay.
 Shield layer Insulation layer is friction
resistant.

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Application: 1 Layer Flex

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Application: Multi-Layer Flex

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Application: Rigid-Flex

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Shielding Method – Pros & Cons

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Shielding Method – Copper Layers: Pros
 Most effective shielding method.
 Controlled impedance capable.
 Best for shielding in higher density
component areas.
 Suitable for all flex and rigid-flex designs.
 Can be extend under flex stiffeners.

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Shielding Method – Copper Layers: Cons
 Negative impact on cost & flexibility.
– Flexibility:
• Cross hatched planes improves flexibility but degrades shielding.
– Cost:
• Added process steps and materials due to increased layer count.
 Limited application to flex circuits of greater than 2 layers
depending upon bend requirements.
– Increased thickness and reduced bend capability.
 Consumes additional circuit real estate due to added
vias required to access SMT components.

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Shielding Method – Silver Ink: Pros
 Effective shielding method.
 Less costly than copper layer shields.
 More flexible than copper layer shields.
 Can be extended under stiffeners.
 Can be added, with limitations, to higher layer count
designs.
 Traditional method used for decades.

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Shielding Method – Silver Ink: Cons
 Added process steps and materials.
– 1-2 silver ink layers (screening & baking).
– 1-2 additional coverlays.
 Reduced bend capability.
– Increased flex thickness.
 Not recommended for controlled impedance.
 Not compatible with rigid-flex designs.
 Very limited application in high density component areas.
– Limited by min. web thickness.

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Shielding Method – Silver Ink: Cons (continued)

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Shielding Method – Shield Films: Pros
 Very effective shielding.
 Most cost-effective and flexible solution.
 Can be used in component areas with some
limitations.
 Suitable for all flex and rigid-flex designs.
 Most used solution for non-controlled
impedance designs.

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Shielding Method – Shield Films: Pros (continued)
 Shield Effect

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Shielding Method – Shielding Film: Cons
 Not recommended for controlled
impedance designs.
– Increased impedance tolerance.
– Difficult to achieve required dielectric
thickness.
 Limited capability in higher density
component areas.
– Due to min. web thickness
requirements.
 Exposed ground circuit at flex area
outline.

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Shielding Method – Gerber Design

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Gerber Design – Copper Shields
 Easiest Gerber design solution.
– Simple process of adding external ground planes.
 Supported by all CAD systems.
 Vias required to rout circuits up SMT components.
 Via stitching in flex areas (Faraday cage) possible.
– Limits flexibility.
– Vias in flex areas not recommended by IPC 2223.

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Gerber Design – Copper Shields (continued)

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Gerber Design – Silver Ink Shields
 Most complex Gerber design
solution.
– Not well-supported (if at all) by CAD
systems.
 Shield designed as an additional
coverlay:
– 0.020” oversize to primary coverlay.
– 0.050” min. web thickness.
– 0.020” min. setback from part
outline.

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Gerber Design – Silver Ink Shields
 Secondary coverlay required.
– 0.010” oversize to primary coverlay
to encapsulate silver ink.
– 0.020” selective access holes to
ground shield.
 Ground Circuits.
– min. 0.020” trace width.
 Most often requirements defined in
mechanical and left to manufacturer
to design.
 Not part of CAD database.

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Gerber Design – Shielding Film
 Simple Gerber design solution.
 Treated as addition coverlay/mechanical layer
– 0.010” oversize to coverlay.
– Min web thickness = 0.030”.
 Selective access holes, 0.020”, in coverlay
required to ground shield.
 Shield extended to part outline preferred.
 Epoxy strain reliefs required for
rigid-flex designs.
– Seals shield layer to rigid areas.

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Gerber Design – Shielding Film
 Elimination of exposed edge ground requires shield to be postage stamped in
place
– Size and shape may prevent
– Added cost to manufacture
and locate shield

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Gerber Design – Shielding Film (continued)
 Cannot be extended under stiffeners
– Poor adhesion due to slip properties of Shield insulation layer

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Summary
 EMI shielding of flex circuits or flex areas in rigid-flex is easily accomplished.
 Most applications have at least 1 if not more available shielding options.
 Preferred shielding solution dependent upon design requirements.
– Flexibility required to meet min. bend requirements.
– Controlled impedance.
– Flex area layer count.
 All methods provide sufficient shielding to meet stringent EMI requirements.
 Most used methods today are copper layers and shield films.
 Silver ink demand and supply is diminishing.

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Our Products
Battery Packs Flex & Rigid-Flex PCBs Cable Assemblies Printed Circuit Boards
RF Products User Interfaces Flexible Heaters EC Fans & Motors

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Free Online Technical Resources
 Epec’s Blog
– https://blog.epectec.com/
– Paul’s Author Page – https://blog.epectec.com/author/paul-tome
 Design Guides & Ebooks
– https://www.epectec.com/guides/
 Technical Articles
– https://www.epectec.com/articles/
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– https://www.epectec.com/webinar/

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ITAR – NetVia Group
 Located in Dallas, TX
 26,000 sq ft of manufacturing space
 25+ Years PCB Experience
 Up to 40 Layers
 Embedded Resistors
 Heavy & Extreme Copper
 RF & Microwave PCBs
 Flex & Rigid Flex

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Q&A
 Questions?
– Enter any questions you may have
in the control panel
– If we don’t have time to get to it, we
will reply via email

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Thank You
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