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Manufacturing That Eliminates Risk & Improves Reliability
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
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– 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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