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AltiumLive 2017:ANNUAL PCBDESIGN SUMMIT
Tara DunnOmni PCB
Event Location,October 3, 2017
Why would you use flexible circuits?
Enabling Technology
Flex Materials and Best Practices
Case Studies
Specialty Circuits
Why Use Flexible Circuits
Cost Considerations
2
3
Agenda
1
4
Real World Advice from Industry Experts
4
5
6
Why would you use flexible circuits?
Solve Product Packaging Problems
Why would you use flexible circuits?
Reduce Assembly Costs
Why would you use flexible circuits?
Reduces Both Weight and Volume
Why would you use flexible circuits?
They Facilitate Dynamic Flexing
Why would you use flexible circuits?
Thermal Management
Why would you use flexible circuits?
Improve Product Aesthetics & Bio-compatibility
Why would you use flexible circuits?
Intrinsically More Reliable & Reduce The Opportunity For Operator Error
Flex Materials and Best Practices
Case Studies
Specialty Circuits
Why Use Flexible Circuits
Cost Considerations
2
3
Agenda
1
4
Real World Advice from Industry Experts
4
5
6
Base material types and design tips
Base Materials
Base material types and design tips
Common miscommunication
Base material types and design tips
Conductor Routing Practices
Maintain smooth transitions, avoid sharp edges
Key: Communicate operational requirements to your fabricator, especially with dynamically flexing applications
Base material types and design tips
Conductor Routing Practices
Base material types and design tips
Conductor Routing Practices
Use large fillets at the trace to pad interface
Base material types and design tips
Conductor Routing Practices
Consider Tear Strips for added
support
Base material types and design tips
Conductor Routing Practices
Keep transitions at least .030” from fold line
Coverlay types and design tips
Coverlay Options and Selection Criteria
Shielding types and design tips
Shielding Options
Cross hatch for greater flexibility. When using solid copper, be aware of quickly increasing thickness and rigidity for bending and folding.
Shielding options and design tips
Stiffener Types
.030” overlap to reduce stress point
Flexing and Bending
Bending Recommendations
Single Metal Layer: 3-6 times material thickness
Two Metal Layers: 7-10 times material thickness
Multilayer Flex: 15-20 times material thickness
Dynamic Flexing: 20-40 times material thickness.
Thru holes should be placed at least .050” away from any bend areas
Flexing and Bending
Tips and Tricks To Improve Flexibility
Route traces to second side and remove copper in flexing area
Cross hatch copper
Un-bonded layers
Consider Button-Plating to eliminate ED copper on panel when creating the PTH
Remove Material
Rigid Flex
Rigid Flex
Key Points:
• Adhesiveless Materials
• Bikini Cut the coverlay(.050” into the rigid areas)
• PTH should be .050” from edgeof flex / rigid interface
Bonded or un-bonded flex layers
Rigid Flex
Strain Relief
Flex Materials and Best Practices
Case Studies
Specialty Circuits
Why Use Flexible Circuits
Cost Considerations
2
3
Agenda
1
4
Real World Advice from Industry Experts
4
5
6
Cost Considerations
Panel Utilization
Cost Considerations
Material
• What are the most commonly stocked materials?
• Most Common Coverlay and cost trade-off’s
• Stiffeners – cost trade off’s
Cost Considerations
Technology
Low Cost Impact:• Complex routing/scoring• Greater than .093” or less than .030” rigid flex• Via Plug
Medium Cost Impact:• Aspect ration > 10:1• Drill hole count > 30K• Non-FR4 materials• Drilled holes < .10”• Line and Space < .005”• Button plating• Controlled Impedance
High Cost Factors• Advanced Technologies• Buried Vias• Layer Count• Material Utilization• Selective Plating• Dual Surface Finish• Line and Space < .004”
Cost Considerations
TechnologyInvolve your Fabricator early with complex designs.
Experience is a great educator. Take advantage of theirs!
Cost Considerations
Our best recommendation for the most cost effective design
Work with your
Fabricator!
Flex Materials and Best Practices
Case Studies
Specialty Circuits
Why Use Flexible Circuits
Cost Considerations
2
3
Agenda
1
4
Real World Advice from Industry Experts
4
5
6
Cost Considerations
Case Study
Medical Application:
Two part numbers designed as 3 layer rigid flex using flex as an outer-layer.• Requires button plating to maintain flexibility in the flex
regions• Required laser cutting of coverlay for surface mount pads• Tight registration required smaller manufacturing panel for
processing
After working with the supplier:• Converted to 4 layer rigid flex• Eliminated the need for button plating the flex layers• Eliminated the need for laser cut coverlay
Even though an additional layer was used and material costs are higher, this redesign resulted in a 20% cost savings.
Cost Considerations
Case Study
Telecommunications Application:
Issue:Customer had 50% failure during installationCopper in the flex area was cracking after being bent several times
Solution:Stack up was redesignedConverted stack up to adhesiveless materialsDecreased flex thickness from 11.8 mils to 8.4 mils (29% decrease)The extra thickness was adding rigidity to the flex area and causing cracking
Over 300 parts have been installed with no failures
Flex Materials and Best Practices
Case Studies
Specialty Circuits
Why Use Flexible Circuits
Cost Considerations
2
3
Agenda
1
4
Real World Advice from Industry Experts
4
5
6
Specialty Circuits
Book Binder
Specialty Circuits
Additive Process
Benefits:
Finer Line and Space: 5 micron to 250 micron -critical to higher resolution devices and smaller packages
Fully Bio-Compatible Materials: Copper or gold traces can be applied directly to polyimide with no chrome or nickel tie coat
Ability to plate on a curved surface: Eliminates an interconnection
RF Advantage: Eliminate the trapezoidal effect of traditional copper etching
Processed on a variety of materials: flex, rigid, ceramic, plastics, fabric
Flex Materials and Best Practices
Case Studies
Specialty Circuits
Why Use Flexible Circuits
Cost Considerations
2
3
Agenda
1
4
Real World Advice from Industry Experts
4
5
6
Real World Advice from Industry Experts
“Unlike rigid designs, capabilities are not universal across most fabricators. Work with the fabricator early in the process to agree on materials, stack-up line/space and fab tolerances.”
“Pay special attention to bend radius limitations and strain reliefs on inside cut and fold regions.”
David Bocchi, Boston Scientific
Real World Advice from Industry Experts
• Avoid abrupt changes in conductor size and direction
• Route conductors uniformly and perpendicular to fold lines
• Radius all cut-lines, NEVER have a sharp inside corner
• Use 3D modeling when laying out your flex
• Get your vendor involved as early in the design process as possible
Real World Advice from Industry Experts
“If PCB Designers want a reasonable amount of success than they need to make sure there documentation matches the Design.”
“Most Important, “The material call out needs to be perfect. As for the actual layout traces should be perpendicular to the trace bend, this is key.”
“For Rigid boards I really don’t need a Drawing and can get the fabrication vendor where he’s going based on material and a starting point. But Flex is different, often called Black Magic in the business.”
Bob Parent, BAE Systems
Real World Advice from Industry Experts
Is it Dynamic Flex or Flex for Install – Be sure to select best suited materials
Book-Bind-Flex - If you require a high layer talk to your fabricator about Book-Bind Flexes.
Anchors - Be sure to add anchor tie points (similar to a thermal relief) from any solder pad to reduce opportunity for pad lift during assembly.
How Flexible is the flex - Be careful to not overspec the copper weight of a flex.
Reduce Adhesives - Reduce coverlay and adhesives in bend radius areas if possible. Reducing the amount of adhesive and or coverlay in a bend radius will keep the material more flexible in that area.
Cut-outs - Use cut-outs to keep the flex more pliable. (Think of a net or chain-link fence)
Consider The Assembly Process - Consider the use of solder pallet to support any SMT reflow that may be needed.
Inside Corners – add a radius to all inside corners (.030” min) to reduce tearing of flex
Modeling: - model or “paper doll” to test proper alignment, orientation and bend areas
Real World Advice from Industry Experts
· Know the construction and the fab process
· Make sure fab. note call-outs are good, based on preliminary review
· Know your manufacturers capabilities matrix.
· Have a mfg/eng review early in the design to ensure it’s buildable with in-stock material &process.
· Mechanically reduce all stress and tear points.
· Via locations are critical avoid placing them close to fold, stress or tear point
· Avoid layer to layer cross talk by offsetting traces on adjacent layers
· Add stiffeners when required make them larger to avoid cracks or stress points
· Learn how a book binder fold works
· Route with smoothing or curved lines avoid sharp bends
· Know how it will bend and if a fold could become a crease which can break the trace
· Make pad patterns bigger to add stress relief
· Add a tear stop piece of dead metal for mechanical rigidity Mike Creeden, San Diego PCB
Thank You
Thank you!
Please contact me for additional information!
Tara DunnOmni PCB, LLCtarad@omnipcb.com507-332-9932www.omnipcb.comwww.pcbadvisor.com
Thank You!
Thanks for your Attention!
Questions?