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Balancing the Electrical and Mechanical Requirements of Flexible Circuits

Publisher: Minco Products, Inc.

Format: PDF
Date: 2009-08-26

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Minco Products, Inc.
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Overview:
This paper examines the electrical and mechanical requirements of flexible circuits, detailing the potential areas of conflict, and ways of overcoming those conflicts. It details the impact of different design issues on the electrical and mechanical performance of flex circuits and presents various enhancements that can be incorporated into flex or rigid-flex circuit designs to improve either electrical or mechanical performance without impairing the other. The importance of clear understanding of design requirements, thoughtful planning, careful choice of materials, and application of best-practices in circuit design for reconciling the conflicts between the electrical and mechanical issues is highlighted. The paper also states that knowledge and experience of a reputable flex circuit manufacturer can be helpful in maximizing both electrical and mechanical performance.

TABLE OF CONTENTS
1.	Electrical Requirements	3
1.1.	Point to Point Connectivity	3
1.2.	Current Requirements	3
1.3.	High-Speed Signal Integrity	3
1.4.	High Component Density	3
1.5.	Terminations	3
2.	Mechanical Requirements	3
2.1.	Physical Size and Shape	3
2.2.	Bending	3
2.3.	Thermal Properties	3
2.4.	Dimensional Stability	3
2.5.	Dielectric Properties	3
3.	Feature Interactions	4
3.1.	Electrical Issues	4
3.2.	Mechanical Issues	4
4.	Balancing Demands	6
4.1.	Micro-Strip Construction	6
4.2.	Placement for Maximum Heat Dissipation	6
4.3.	Cross-Hatching Plane Layers to Increase Flexibility	7
4.4.	Replace Copper Planes with Flexible Conductive Coating	7
4.5.	Unbonding Layers in Critical Areas	8
4.6.	Selective Removal of Cover Material	8
4.7.	Add a "pads-only" Layer	8
4.8.	Heat-Form the Circuit	8
4.9.	Employ Custom Tooling for Cold Forming	8
4.10.	Know Your Termination Schemes before Designing the Circuit	9
5.	Summary	9
6.	Figures
6.1.	Selectively Bonded Layers Can Increase Flexibility in Critical Areas	5
6.2.	Fully Bonded Construction	5
6.3.	A Method Used in Rigid Flex Construction to Reduce or Eliminate the Amount of Acrylic Adhesive in Critcal Areas Is Called a Cut-Back or "bikini" Covers	5
6.4.	The Use of Cross Hatch Plane Layers to Control EMI Can, in Some Cases, Increase Flexibility without Impairing Electrical Performance	7
6.5.	Silver Epoxy Coatings are More flexible Than a Copper Plane	7
6.6.	Unbonded Construction Allows Individual Substrates to Flex Independently	8