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Rigid – Flex Circuit Gerber Layout Guidelines

05.30.14

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Rigid – Flex circuits introduce additional design requirements which need to be accommodated at the Geber Layout phase:

– Rigid to Flex Transition Lines

– Layer Stack ups

– Trace Layout in Flex Areas

Introduction

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Introduction

Guidelines based on IPC 2223C recommended Rigid – Flex Construction(s):

– Ensures the highest degree of reliability and performance

– Key Elements• Adhesiveless Flex Core

• Selective Flex Area Coverlay

• No Flow Prepreg (rigid area layer lamination)

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Definition: Line at which flex layers exit from Rigid area(s)

– Special requirements due to:

• IPC 2223C Selective Coverlay and Material Guidelines

• Manufacturing Methods:

– Rigid Materials (FR4 & Prepreg) are removed from flex areas prior to the layer lamination process

Rigid to Flex Transition Lines

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Rigid to Flex Transition Lines:PTH Hole Spacing

0.050” Min. Requirement:– As measured from edge of drilled hole to “Rigid to Flex” transition line(s)

– Prevents PTH holes from being drilled through Selective Coverlay adhesives

– Accounts for manufacturing and material tolerances

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Rigid to Flex Transition Lines:Copper Feature Spacing

0.025” Min. Clearance (External Layers only)– Allows for manufacturing methods and tolerances during outer layer

imaging processes

– Accounts for prior removal of rigid materials in flex areas

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Rigid – Flex Layer Stack Up Guidelines

Flex Layer Core Thickness(s):

– 0.001” recommended• Improved flexibility, mechanical reliability and bend radius capability

– 0.002” to 0.003” required for impedance controlled designs

Balanced Construction with centrally located Flex Layers Recommended:

– Minimizes potential warp and twist in assembly arrays

– Avoids potential cost adders

– Unbalanced builds possible but should be reviewed with supplier in advance

Balanced Construction Unbalanced Construction

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Rigid – Flex Layer Stack UpGuidelines

Same Finished Thickness in all Rigid Areas:– Avoids sequential lamination processes and significant added costs

– Consult with supplier to determine viability

Odd Layer Counts Allowed:

– E.G.: 5 Layer Rigid with 1 or 3 layers flex etc.

Flex Area Layer Count:– Minimize for thinnest possible construction

• Improved flexibility, reliability and bend radius

Flex Layer Copper Weight:– ½ OZ Copper recommended

• Improved flexibility and mechanical reliability• Allows for impedance controlled circuits

– 1 OZ Copper available for higher current carrying requirements

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Rigid – Flex Layer Stack UpGuidelines

Paired Flex Layers Structure Recommended:– Eliminates flex adhesives from rigid areas for PTH reliability

– Improves flex area flexibility and mechanical reliability

8 Layer Rigid – 2 Layer Flex 8 Layer Rigid – 4 Layer Flex (Air Gap)

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Rigid – Flex Layer Stack UpGuidelines

Impedance Controlled / Shielded Designs:– May require 3 or more flex layers bonded together

– Use of flex adhesives to be minimized to best conform to IPC 2223C

– Potential negative impact on flexibility and bend requirements

– Consult with supplier for best configuration

7 Layer with 3 Flex Layers 8Layer with 4 Flex Layers

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Flex Area Trace Layout Guidelines

Offset Traces from Layer to Layer in Flex Area (if possible)– Improves mechanical flexibility by minimizing “I-Beam” effect

– Impedance Controlled and Shielded Designs will not fully allow due to reference plane requirement

Preferred Not Recommended

Impedance Controlled Design

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Flex Area Trace Layout Guidelines

Straight / Parallel Trace layout is preferred:– Eliminates potential mechanical stress concentrators in bend areas

– If direction change is required then rounded trace corners are recommended

• Up to 45 degree corners are allowed

• 90 degree corners are not recommended

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Our Products

Battery Packs Flex & Rigid-Flex PCB’s User Interfaces

Fans & Motors Cable Assemblies Printed Circuit Boards

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Design Centers & Technical Support

Battery Pack & Power Management – Denver, CO User Interfaces – Largo, FL Fans & Motors – Wales, UK PCB’s – New Bedford, MA & Shenzhen, China Flex & Rigid Flex – Toronto, Canada Cable Assemblies – New Bedford, MA

Our Engineering and Design teams are ready to help our customers create world class and cost effective product solutions.

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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, wewill reply via email.

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For more information email sales@epectec.com.

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