Advanced Rigid-Flex Circuit Constructions

Manufacturing That Eliminates Risk & Improves Reliability

Advanced Rigid-Flex

Circuit Constructions

06.29.17


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Introduction

Todays Rigid-Flex materials and construction methods allow for a wide variety of advanced design configurations.

These options create the opportunity to achieve higher levels of design integration and packing density.


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Introduction

Options Include:

– Higher Flex Layer Counts

– Blind & Buried Via Structures

– ZIF Connections

– Flex Area Components

– Asymmetrical Constructions

– Shielded Flex Areas

– Multiple Rigid Area Thicknesses

In this webinar we will introduce and discuss the benefits and applications of some of the more common advanced rigid-flex circuit board constructions.

Many additional configurations and combinations are available.


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Agenda

Standard Construction Review

Advanced Rigid-Flex Construction Options:

– Odd Number Layer Counts

– Asymmetrical Constructions

– Varying Flex Layer Count Areas

– Integrated ZIF Connections

– Blind & Buried Vias

– Air Gap Flex Layer Constructions

– Multiple Rigid Area Thicknesses

– Shielded Flex Layers


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Standard Rigid-Flex Construction

Symmetrical construction

Even layer counts in both rigid & flex areas

Impedance Control available


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Standard Rigid-Flex Construction

Most common construction (approx. 60%)

Soldmask (LPI)

Layer 1 Base Copper um + Plated 20 um min.

FR-4 (170 tg min.)

Layer 2 Copper

Coverlay:

Coverlay Adhesive:

Layer 3 Copper

Polyimide Core (Adhesiveless) Flex Thickness Rigid

Layer 4 Copper Thickness

Coverlay Adhesive:

Coverlay:

Layer 5 Copper

FR-4 (170 tg min.)


Soldmask (LPI)

Prepreg (2 x 1080, no flow)



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Odd Layer Count Constructions

7 layer Rigid area with 3 Flex layers

Soldmask (LPI)


FR-4 (170 tg min.)

Layer 2 Copper

Coverlay:

Coverlay Adhesive:

Layer 3 Copper

Polyimide Core (Adhesiveless)

Adhesive Rigid


Polyimide Flex Thickness

Layer 5 Copper

Coverlay Adhesive:

Coverlay: 25 um

Layer 6 Copper

FR-4 (170 tg min.)


Soldmask (LPI)




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5 layer Rigid area with 1 Flex layer

Soldmask (LPI)


FR-4 (170 tg min.)

Layer 2 Copper

Coverlay:

Coverlay Adhesive:

Layer 3 Copper Flex Thickness Rigid

Polyimide Core (Adhesiveless) Thickness

Layer 4 Copper

FR-4 (170 tg min.)


Soldmask (LPI)




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3 layer Flex area configuration allows for two sided shielding requirements in flex areas.

– Stripline Impedance Control

– RF & EMI Requirements

Odd layer counts can apply to both flex & rigid areas independent of each other.

Minimizes flex area thickness for improved flexibility and mechanical bend capability / reliability.

IPC 2223C compliant.

Reduces cost by minimizing total number of flex layers required.


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Asymmetrical Constructions

Applications:

– Convoluted impedance requirements

– Blind via constructions

• Minimizes blind via aspect ratio for improved manufacturability reliability.

May result in warp & twist in assembly arraywhich may require a hold down fixturefor transport through assembly.


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Asymmetrical Constructions

Soldmask (LPI)

Layer 1 Base Copper 18 um + Plated 35 um min.

FR-4 (170 tg min.)

Layer 2 Copper


Layer 3 Copper

FR-4 (170 tg min.)

Layer 4 Copper Rigid

Coverlay: Thickness

Coverlay Adhesive:

Layer 5 Copper

Polyimide Core (Adhesiveless) Flex Thickness

Layer 6 Copper

Coverlay Adhesive:

Coverlay:

Layer 7 Copper

FR-4 (170 tg min.)





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Varying Flex Layer Count Constructions

Allows for tighter bend capabilities in reduced flex layer count area.

Multiple configurations available.

Requires use of “Air Gap” flex layer construction.


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Varying Flex Layer Count Constructions

Soldmask


FR-4 (170 tg min.)

Coverlay:

Coverlay Adhesive:

Layer 2 Copper

Polyimide Core (Adhesiveless) Flex


Coverlay Adhesive:

Coverlay: Rigid

Thickness

Coverlay:

Coverlay Adhesive:

Layer 4 Copper

Polyimide Core (Adhesiveless) Flex


Coverlay Adhesive:

Coverlay:

FR-4 (170 tg min.)


Soldmask

AIR GAP





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Integrated ZIF Tail Constructions

Eliminates the need for a ZIF connector and separate flex circuit.

Reduces real-estate requirements in rigid area(s).

Improves reliability through elimination of points of interconnect.

– ZIF connector solder joints, ZIF finger contacts

Available in a wide variety of configurations.


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Integrated ZIF Tail Constructions

Soldmask (LPI)


ZIF

Adhesive Thickness

Polyimide Core (Adhesiveless) Rigid Thickness Flex Thickness

Layer 2 Copper

Coverlay Adhesive:

Coverlay:


Soldmask (LPI)



FR-4 (170 tg min.)

Polyimde Stiffener

FR-4 (170 tg min.)


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Blind & Buried Constructions

Applications: Similar to Rigid PCB Blind & Buried Constructions

– High density BGA applications with via in pad etc.

May require an asymmetrical construction if blind vias interconnect to flex layers.

Configurations may be limited due to number of sequential lamination cycles required. Less than Rigid PCBs due to material dimensional tolerances and manufacturing methods.

Via fill and cap available.


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Blind & Buried Constructions

Soldmask (LPI)


FR-4 (170 tg min.)

Layer 2 Copper


Layer 3 Copper

FR-4 (170 tg min.)

Layer 4 Copper

Coverlay:

Coverlay Adhesive:

Layer 5 Copper



Coverlay Adhesive:

Coverlay:

Layer 7 Copper

FR-4 (170 tg min.)





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Flex Layer Air Gap Constructions

Flex layers configured as independent pairs of 2.

Allows design to meet IPC 2223C design guidelines.

– Construction results in no flex adhesives in rigid areas.

– Preferred configuration for 4 or more flex layers.

Provides greater flexibility due to flex layers bendingindependent of each other.


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Flex Layer Air Gap ConstructionsSoldmask


FR-4 (170 tg min.)

Coverlay:

Coverlay Adhesive:

Layer 2 Copper


Layer 3 Copper

Coverlay Adhesive:

Coverlay:

Coverlay:

Coverlay Adhesive:

Layer 4 Copper Rigid

Polyimide Core (Adhesiveless) Flex Thickness Thickness

Layer 5 Copper

Coverlay Adhesive:

Coverlay:

Coverlay:

Coverlay Adhesive:

Layer 6 Copper


Layer 7 Copper

Coverlay Adhesive:

Coverlay:

FR-4 (170 tg min.)


Prepreg (3 x 1080, no flow) AIR GAP

AIR GAP





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Multiple Rigid Area Thickness Construction

Rigid area thickness vary between sections.

Practically limited to 2 rigid thicknesses maximum.

May have limits in rigid area thicknesses due to required materials.

Very costly construction

– Manufacturing process is equivalent to making 2 boards to get 1.


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Multiple Rigid Area Thickness Construction

Soldmask (LPI)


Soldmask (LPI)

Layer 2 Copper + Plating

Coverlay:

Coverlay Adhesive:

Layer 3 Copper

Polyimide Core (Adhesiveless) Rigid Thickness 1 Rigid

Layer 4 Copper Thickness 2

Coverlay Adhesive:

Coverlay:

Layer 5 Copper + Plating

Soldmask (LPI)


Prepreg

Prepreg

FR-4 (170 tg min.)

FR-4 (170 tg min.)

Prepreg (1 x 106, + 1 x 1080, no flow)

Prepreg (1 x 106, + 1 x 1080, no flow)




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Shielded Flex Layers Construction

Allows for effective EMI & RF shielding without additional copper layers.

– Reduced cost

– Thinner flex area construction for improved flexibility

Uses specialized shielding films (i.e.: Tatsuta, APlus etc.)

Shielding films are laminated to Flex areaCoverlays and interconnect to groundthrough selective Coverlay openings andelectrically conductive adhesive.


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Shielded Flex Layers Construction

Soldmask (LPI)


Shield Layer

Coverlay:

Coverlay Adhesive:

Layer 2 Copper



Coverlay Adhesive:

Coverlay:

Shield Layer


FR-4 (170 tg min.)

FR-4 (170 tg min.)

Prepreg (2 x 1080 no flow)

Prepreg (2 x 1080 no flow)


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Summary

The combination of todays Rigid PCB and Flex circuit technology allows for a very wide variety of Rigid-Flex constructions that can add a significant amount of functionality, integration and overall packaging reduction to a design.

Majority of the specific constructions can also be combined together to create an almost endless number of configurations.


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Our Products

Custom Battery Packs Flex & Rigid-Flex PCB’s High Reliability SMART HMIs

RF Product Solutions Cable Assemblies Printed Circuit Boards


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Design Centers & Technical Support

Battery Pack & Power Management – Denver, CO

SMART User Interfaces – Largo, FL

Flex & Rigid Flex – Toronto, Canada

RF Products – New Bedford, MA & Largo, FL

Cable Assemblies – Largo, FL

Printed Circuit Boards – New Bedford, MA & Shenzhen, China

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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Thank YouCheck out our website at www.epectec.com.

For more information email [email protected].

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Technology

Advanced Rigid-Flex Circuit Constructions