The document outlines the complexities of manufacturing flex and rigid-flex printed circuit boards (PCBs), emphasizing the need for streamlining designs to reduce costs and enhance reliability. It discusses the various materials and processes involved, the importance of Design for Manufacturability (DFM), and the role of early manufacturer input in optimizing designs. Key features such as impedance requirements, additional elements like stiffeners and shield layers, and their impact on manufacturing efficiency are also highlighted.

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Successful Flex & Rigid-Flex Designs
for Streamlining Production
04.25.2019

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Introduction
 Definition: Streamlined
– Designed or arranged to offer the least resistance.
– Reduced to essentials.
– Effectively organized or simplified.

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Introduction
 Flex & Rigid-Flex:
– More materials and production process steps
than rigid PCBs.
– Many more “additional items” than Rigid PCBs.
• Additional materials & process steps
• May interact with one another and create
additional technical challenges
– Streamlining a flex or rigid-flex design has a
much greater impact on delivery and cost.

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Introduction – 2 Layer Rigid vs 2 Layer Flex
 Rigid PCB:
– Materials: Rigid core, soldermask, silkscreen
– Processes: Drilling, plating, imaging, soldermask, surface finish,
silkscreen, ET, outline routing
– Totals: Materials = 3, Processes = 8
 Flex Circuit:
– Materials: Flex core, coverlay (and or soldermask), silkscreen,
stiffeners (FR4 and or Polyimide), PSA
– Processes: Drilling, plating, imaging, coverlay routing / drilling,
coverlay lamination, soldermask (if required), surface finish,
stiffener drilling / routing, stiffener lamination, PSA drilling /
routing, PSA application, silkscreen, ET, outline profiling
– Totals: Materials = 6, Processes = 17

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Introduction – 4 Layer Rigid vs 4 Layer Rigid-Flex
 Rigid PCB:
– Materials: Rigid cores, prepreg, soldermask, silkscreen
– Processes: Inner layer imaging, layer lamination, drilling, plating, outer layer
imaging, soldermask, surface finish, silkscreen, ET, outline routing
– Totals: Materials = 4, Process = 10
 Flex Circuit:
– Materials: Rigid cores, prepreg, flex core, coverlay, soldermask, silkscreen,
stiffeners (FR4 and or Polyimide)
– Processes: Inner layer flex imaging, coverlay routing / drilling, coverlay
lamination, stiffener drilling / routing, stiffener lamination, layer lamination,
drilling, plating, outer layer imaging, soldermask, surface finish, silkscreen,
ET, flex area rigid material removal, outline profiling
– Totals: Materials = 7, Processes = 17

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Agenda
 Design for Manufacturability Review (DFM)
 Design & Construction
 Material Selection
 Manufacturing Data Sets: Complete, Detailed, Accurate
 Impedance Requirements
 Flex Area Via & Plated Through Holes
 Additional Features
– Stiffeners, PSAs, Shield Layers, Epoxy Strain Reliefs

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Design for Manufacturability Review (DFM)

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Design for Manufacturability Review (DFM)
 Key early step in the design
development process.
 Initial step at the concept stage to
valid design direction.
 Repeated multiple times for
sophisticated design.
 Prevents future design road blocks
and delays.

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IPC 2223 Design Standard
 Industry Capabilities
 Manufacturability
 Reliability

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Design & Construction

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Design & Construction
 Rigid-Flex Construction:
– Mid flex layers preferred for
balanced build.
– Minimizes warp & twist in
arrays.
– Simplified manufacturing
process.
– Improved flexibility.

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Design & Construction
 Rigid-Flex vs Flex with Stiffeners:
– Which solution dependent upon component
requirements.
– Flex Circuit with Stiffener:
• More cost effective due to reduced material
requirements and process step
• Application limitations
– Rigid-Flex:
• More capable technology
• Increased costs due to materials and additional process
steps

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Design & Construction
 Part Size & Shape:
– Significant cost impact due to
material requirements, material
utilization, number of production
panels required and yield rates.
– Manufacturer input for optimum
assembly array configuration.

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Design & Construction
 Initial Draft  Revised Design

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Material Selection

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Material Selection
 Common Industry Materials:
– Copper: ½ - 1 OZ
• Rolled Annealed & Electrodeposited
– Flex cores: 1- 3 mil
• Adhesiveless & Adhesive Based
– Coverlays: ½ - 1 mil thickness Polyimide + ½ mil to
2 mil adhesive
 Material Formats:
– Offshore: 250mm wide roll format (500 mm available)
– Domestic: 18” x 24” panels
Stay within the industry standards for improved delivery & reduced costs.

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Manufacturing Data Sets:
Complete, Detailed, Accurate

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Gerber Data Sets: Complete, Detailed, Accurate
 Manufacturing & QC Standards
 Material Specifications
 Critical Dimensions
 Material Stack-up
 Complete Gerber Data Set
– Stiffeners
– PSAs
– Shield Layers
– Epoxy Strain Reliefs
Eliminates interpretation errors.

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Impedance Requirements

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Impedance Requirements
 Impedance Construction:
– Stripline (3 layer) vs Surface Micro Strip (2 Layer)
• Surface Micro preferred due to reduced flex thickness
– Combination of Dielectric / Line Width / Spacing:
• Dielectric: 2 – 3 mil
• Line Widths: 3 – 4 mil
• Line Spacing: 5 – 7 mil
– Many Designs Not Optimized for Flex Applications
• PCB design rules applied using thicker cores. Limits flexibility and mechanical reliability.
• May not meet minimum bend requirements mechanical reliability.

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Flex Area Via & Plated Through Holes

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Flex Area Vias & Plated Through Holes
 Application:
– Flex Section Components
– Shield Layer Via Stitching
 Processes & Cost:
– Additional drilling & plating processes
– Plating process = Selective pad plate
– May require additional processes depending upon surface
finish
Apply when required. Avoid if possible.

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Additional Features
Stiffeners, PSAs, Shield Layers, Epoxy Strain Reliefs

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Additional Features: Stiffeners
 Applications:
– Component Area Support
– ZIF Contact area thickness specifications
 Added materials, processes & cost for each
different stiffener.
– Multiple lamination cycles, profiling & drilling
process.
While stiffener costs are minimal, delivery can be significantly impacted.
Apply where required.

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Additional Features: PSA
 Application:
– Adhere flex circuit within enclosure
– Affix Zero bend radius areas to prevent bend
from being re-opened
 Added materials, processes & cost for each
different PSA.
– Multiple profiling, drilling, and application
processes
While PSA costs are minimal, deliveries can be significantly extended.

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Additional Features: Shield Layers
 Application:
– EMI & RF shielding
– Replaces additional copper layers
– Improved flexibility and lower cost over additional
copper layers.
– Interconnects to ground with conductive adhesive
and selective coverlay openings.
 Preferred option for shielding non-impedance-
controlled designs.
– Manufacturers assistance required to incorporate
shield layers into design / data set.

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Additional Features: Epoxy Strain Reliefs
 Application:
– Acts as a mechanical strain relief at the rigid to flex
transitions.
– Prevents flex from creasing at a rigid section if bent in
close proximity.
 Inexpensive option but may significantly impact
delivery.
– Manual application process due to 2-part epoxy
system.
– Applied to 1st side, baked, applied to 2nd side and
baked.
Use only where and when required.

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Summary

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Summary
 Streamlining or optimizing a flex or rigid-flex circuit design starts at the
concept stage.
 Reviewed multiple times as design is developed and finalized.
 Input from manufacturer recommended.
– Design elements can and will interact. Potentially creating additional
manufacturing complexities and costs.
– Material selection and utilization feedback.
 Evaluate all design elements at the prototype stage and adjust design
to improve optimization.

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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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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
Check out our website at www.epectec.com.
For more information email sales@epectec.com.
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