The flex and rigid-flex manufacturing process is inherently more complex with more process steps than those found in a rigid PCB of similar technology. When it comes to flex PCB designs, this is driven by the difference in materials combined with the many added items or features that can be incorporated into a design.
These include stiffeners (of varying materials / thickness / locations), pressure sensitive adhesives, shield layers, strain reliefs, etc. For rigid-flex designs this can become additionally complex as all the available flex items are combined with all the technical items found in rigid PCBs. These items potentially interact and can negatively impact the efficiency of the production process.
Streamlining is defined as making a process more efficient and effective. Having a design that streamlines the production process will have the benefits of improved delivery times, reduced part cost, improved manufacturing yield, and even potentially improved long-term part reliability.
In this webinar where we review the many areas of flex and rigid-flex designs that can impact how streamlined a design is for production.
For more information on our flex and rigid-flex PCB solutions visit https://www.epectec.com/flex/.
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Successful Flex & Rigid-Flex Designs for Streamlining Production
1. Manufacturing That Eliminates Risk & Improves Reliability
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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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
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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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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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 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
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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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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