Sectional Design Standard for Flexible/Rigid-Flexible Printed Boards

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Hugh Lewis
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1 Sectional Design Standard for Flexible/Rigid-Flexible Printed Boards Developed by the Flexible Circuits Design Subcommittee (D-) of the Flexible Circuits Committee (D-0) of IPC Supersedes: IPC-2223C - November 20 IPC-2223B - May 2008 IPC-2223A - June 2004 IPC November 998 IPC-D January 987 Users of this publication are encouraged to participate in the development of future revisions. Contact:

2 Table of Contents SCOPE.... Purpose....2 Classification of Products Printed Board Type Installation Uses Revision Level Changes APPLICABLE DOCUMENTS IPC Joint Industry Standards GENERAL REQUIREMENTS Design Modeling Design Layout Mechanical Layout Efficiency (Consider Final Panelization) Fabrication Drawing Recommendations Schematic Test Requirement Considerations Environmental Mechanical/Flexural MATERIALS Material Selection Material Options Dielectric Materials (Including Prepreg and Adhesives) Preimpregnated Bonding Material (Prepreg) Adhesives (Liquid) Flexible Adhesive Bonding Films (Cast Adhesive or Bondply) Conductive Anisotropic Adhesives Cover Materials Conductive Materials (Surface Finishes) Electrolytic Copper Plating Nickel Plating Tin-Lead Plating Solder Coating Other Metallic Coatings Electronic Component Materials (Buried Resistors and Capacitors) Conductive Coatings for Shielding Organic Protective Coatings Solder Mask Conformal Coating Marking and Legend... 5 MECHANICAL AND PHYSICAL PROPERTIES Fabrication Requirements Bare Printed Board Fabrication Roll to Roll Fabrication Product/Printed Board Configuration Circuit Profile (Outline) Rigid Area Considerations Flexible Areas Preforming Bend Differential Lengths Shielding Ground/Power Plane Stiffeners and Heat Sinks Strain Relief Fillet Guidelines for Flexible and Rigid-Flex Printed Boards Assembly Requirements Mechanical Considerations Array Sub-Pallets for Flexible and Rigid Printed Boards Single Part Sub-Pallets Non-Palletized Flexible and Rigid-Flex Printed Boards Moisture Infrared Preheats and Reflow Adhesive T g Dimensioning Datum Features ELECTRICAL PROPERTIES Electrical Considerations Impedance and Capacitance Control Impedance Modeling Software Material Thickness and Stack up Conductor Pitch Narrow Conductors Differential Impedance Unbonded Flexible Impedance Controlled Layers ( Loose-leaf layers ) Modifications to Shield Layers Dielectric Constant Changes Over Frequency THERMAL MANAGEMENT COMPONENT AND ASSEMBLY ISSUES General Placement Requirements Standard Surface Mount Requirements v

3 September Lands for Surface Mounting Constraints on Mounting to Flexible Sections Interfacial Connections Offset Lands HOLES/INTERCONNECTIONS General Requirements for Lands with Holes Land Requirements Annular Ring Requirements Eyelet or Standoff Land Area Considerations Land Size for Non-Plated Component Holes Land Size for Plated-Through Component Holes Thermal Relief in Conductor Planes Surface Mount Components Nonfunctional Lands Land-to-Conductor Transition Unsupported Edge Conductors/Fingers Holes Unplated Component Holes Plated Component Holes Copper Filled Vias Coverlay Access Openings Coverlay Access, Unsupported Lands Coverlay Access, Holes Coverlay Access Spacing Land Access/Exposed Lands Type Land Access, Opposite Sides CONDUCTORS Conductor Characteristics Conductor Routing Conductor Edge Spacing Land Characteristics Large Conductive Areas DOCUMENTATION QUALITY ASSURANCE APPENDIX A Design Tutorial Figures Figure - Type Single-Sided Flexible Printed Board Adhesive Substrate Construction... Figure -2 Type Single-Sided Flexible Printed Board Adhesiveless Substrate Construction... Figure -3 Type 2 Double-Sided Flexible Printed Board Adhesive Substrate Construction... 2 Figure -4 Type 2 Double-Sided Flexible Printed Board Adhesiveless Substrate Construction... 2 Figure -5 Type 3 Multilayer Flexible Printed Board Adhesive Substrate Construction... 2 Figure -6 Type 3 Multilayer Flexible Printed Board Adhesiveless Substrate Construction... 2 Figure -7 Type 4 Rigid-Flex Printed Board Adhesive Substrate Construction... 3 Figure -8 Type 4 Rigid-Flex Printed Board Adhesiveless Substrate Construction... 3 Figure -9 Type 5 Flexible or Rigid-Flex Printed Board without PTHs Adhesive Substrate Construction... 3 Figure -0 Type 5 Flexible or Rigid-Flex Printed Board without PTHs Adhesiveless Substrate Construction... 3 Figure 3- Dimensional Modeling... 5 Figure 3-2 Final Panelization... 5 Figure 4- Flexible Cross-Sectional Construction Examples... 6 Figure 4-2 Unbonded Flex Cross-sectional Construction of Rigid Flex... 6 Figure 4-3 Plating for Adhesiveless Substrate Applications... 0 Figure 4-4 Selective Plating for Adhesive Substrate Applications... 0 Figure 5- Circuits Nested On a Panel... 2 Figure 5-2 Special Flexible Printed Board Features... 2 Figure 5-3 Cutout with a Drilled Hole... 2 Figure 5-4 Reinforcement Patch for Flex Area... 2 Figure 5-5 Slits and Slots... 3 Figure 5-6 Spacing of PTH from Rigid to Flex Interface.. 3 Figure 5-7 Reduced Bend Radii... 4 Figure 5-8 Conductors in Bend Areas... 4 Figure 5-9 Bend/Crease Areas Center Lines... 5 Figure 5-0 Neutral Axis Ideal Construction... 5 Figure 5- Definition of Bend Ratio... 6 Figure 5-2 Irregular Folds... 7 Figure 5-3 Differential Printed Board Lengths... 8 Figure 5-4 Differential Printed Board Lengths, Rigid-Flex... 8 Figure 5-5 Bookbinder Figure 5-6 Staggered Flexible Layer Bands Figure 5-7 Staggered Flexible Layer Bands Figure 5-8 Typical Example of Copper Removal for Flexible Shielding... 2 Figure 5-9 Stiffener Thickness Preferred in Order to Apply Strain Relief Fillet... 2 Figure 5-20 Strain Relief Figure 5-2 Rigid Rails for Single Part Sub-Pallets Figure 5-22 Establishing Datums Figure 6- Adjustment to Dielectric Thickness between Rigid and Flexible Regions Figure 6-2 Conductor Pitch for Differential Pairs vi

4 Figure 6-3 TDR Waveform for Type 2 Flexible Printed Board Figure 6-4 Buckling of Unbonded Flexible Layers Figure 6-5 Cross Hatching Figure 9- Conductor to Land Transitions Figure 9-2 Sculptured, Straight, Tapered Fingers Figure 9-3 Sculptured, Formed for Surface Mount Figure 9-4 Sculptured, Formed for Through-Hole Figure 9-5 Straight Fingers for Lap Soldering to Printed Board Figure 9-6 Adhesive Squeeze Out Where Fingers Exit Insulation Figure 9-7 Laser Ablated Window Figure 9-8 Broken Fingers Resulting from Poor Handling Figure 9-9 Fingers Connected with a Foil Buss Bar Figure 9-0 Insulator Buss Bar with Notched Fingers Figure 9- Fingers Attached to a Support Bar Figure 9-2 Staggered Base/Coverlay Edges Used to Reduce Stress Points Figure 9-3 Sculptured Flex Showing the Foil Thickness Transition Figure 9-4 Fingers Brazed to Circuit Lands Figure 9-5 Bonding of Unsupported Fingers to Printed Board with Reinforcement Figure 9-6 Coverlay Access Openings and Exposed Unsupported Lands Figure 9-7 Coverlay Access Opening for Unsupported Lands Figure 9-8 Coverlay Access Openings and Exposed Supported Lands Figure 0- Conductor Routing, Rigid-Flex Transition Tables Table 4- Characteristics of Typical Flexible Dielectrics... 8 Table 4-2 Minimum Average Copper Thickness, mm [in]... 9 Table 9- Minimum Standard Fabrication Allowance for Interconnection Lands, mm [in] Table 9-2 Nonfunctional Land Considerations Table 9-3 Typical Foil Options for Designing for Flex Circuits with Unsupported Fingers... 3 Table 9-4 Common Brazed Finger Options vii

5 Sectional Design Standard for Flexible/ Rigid-Flexible Printed Boards SCOPE This standard establishes the specific requirements for the design of flexible and rigid-flexible printed board applications and its forms of component mounting and interconnecting structures. The flexible materials used in the structures are comprised of insulating films, reinforced and/or non-reinforced, dielectric in combination with metallic materials. These interconnecting boards may contain single, double, multilayer, or multiple conductive layers and can be comprised wholly of flex or a combination of both flex and rigid.. Purpose The requirements contained herein are intended to establish specific design details that shall be used in conjunction with IPC-222 and may also be used in conjunction with IPC-2222 for the rigid sections of rigid-flex circuits..2 Classification of Products Classification type and use of products shall be in accordance with IPC-222 and as stated in.2. and Printed Board Type This standard provides design information for different flexible and rigid-flex printed board types. Printed board types are classified as: Type Single-sided flexible printed board containing one conductive layer, with or without stiffener, and constructed using an adhesive or adhesiveless substrate (see Figure - and Figure -2) IPC-2223d-- IPC-2223d--2 Figure - Type Single-Sided Flexible Printed Board Adhesive Substrate Construction Note : Access Hole. Note 2: Coverlay. Note 3: Adhesive. Note 4: Substrate. Note 5: Copper Pad. Figure -2 Type Single-Sided Flexible Printed Board - Adhesiveless Substrate Construction Note : Access Hole. Note 2: Coverlay. Note 3: Adhesive. Note 4: Adhesiveless Substrate. Note 5: Copper Pad.

Sectional Design Standard for High Density Interconnect (HDI) Printed Boards

IPC-2226 ASSOCIATION CONNECTING ELECTRONICS INDUSTRIES Sectional Design Standard for High Density Interconnect (HDI) Printed Boards Developed by the HDI Design Subcommittee (D-41) of the HDI Committee