Camera Rigid Flex PCB
Name: Camera just scratched
Rigid Board : 6 Layer Rigid PCB
Flexible PCB 2 Layer
Board thickness: 0.9mm
Copper thickness oz: 1oz
Material: IT180A + AK
Type: Car HD Camera
Technical features: rigid-flex structure
Application: Car Camera
Introduction
Rigid-flex PCBs provide the ability to integrate multiple rigid PCBs interconnected using flexible circuits in a single assembly. The combination of rigid and flexible materials in one board allows three-dimensional packaging and increased component density within electronic devices.
6 layer rigid-flex refers to a board stackup with 6 conductive copper layers. This article will provide an overview of 6 layer rigid-flex PCB technology covering:
- Benefits and applications
- Construction and materials
- Fabrication process
- Design guidelines
- Assembly considerations
- Cost impact
Benefits of 6 Layer Rigid-Flex PCBs
Compared to conventional rigid boards, 6 layer rigid-flex PCBs offer the following advantages:
Increased Component Density
Folding rigid sections vertically allows placing components on both sides of stacked boards for space and height reduction.
Simplified Assembly
Replacing discrete flexible cables and wire harnesses with integrated flexi-rigid board reduces assembly labor and errors.
Enhanced Flexibility
Eliminates inter-board connectors by running flexible circuits between rigid sections. Accommodates complex motion paths.
Improved Serviceability
Modules can be independently removed for repair/upgrade without affecting other sections by separating along flex bends.
Reduced Weight
Inter-board cables have heavier insulation than thin flexible layers.Removes extraneous housing needed for discrete cables.
Lower Costs
Fewer connectors, simpler assembly, higher density save on materials cost and manufacturing expenses.
Signal Integrity
Better high speed performance by minimizing discontinuities through maintained impedance in traces spanning rigid and flex sections.
Reliability
Avoids reliability risks associated with external wiring and interconnections.
Applications of 6 Layer Rigid-Flex PCBs
The unique capabilities of rigid-flex make them ideal for the following applications which require packaging density, versatility and reliability:
- Wearable devices
- Medical electronics
- Consumer gadgets
- Robotics and UAVs
- Automotive electronics
- Industrial equipment
- Military systems
6 layer rigid-flex technology provides adequate routing channels to implement complex high density circuits for such miniaturized and high performance products.
Rigid-Flex PCB Construction
6 layer rigid-flex consists of:
- Multiple layers of copper clad rigid FR-4 material
- Layers of adhesive-based flexible dielectric like polyimide
- Coverlay bonding the flexible layers
The main rigid section has 6 copper layers. The flex sections integrate 2-6 layers depending on routing needs. Sections are held together by an adhesive. Plated thru holes provide interconnects between layers.
Rigid sections provide mechanical strength for component mounting and heatsinking. Flex layers enable out-of-plane motion and 3D assembly. Different rigid and flex materials can be combined for optimal electrical and thermal performance.
Fabrication Process
6 layer rigid-flex PCB fabrication involves:
Layer Bonding
Rigid and flex core layers are bonded together using adhesive sheets. FR-4 and polyimide are commonly used. Alignment is critical.
Hole Drilling
Mechanical and laser drilling create thru holes for layer interconnection in rigid sections.
Metallization
Copper layers are added using processes like direct plate, pattern plate and print-and-etch. Plated thru hole walls are also metallized.
Lithography
Photoimaging transfers the circuit layout onto multiple rigid and flex layers.
Etching
Unwanted copper is accurately etched away to form the planned tracks and gaps.
Coverlay Addition
Adhesive-based coverlay is laminated onto the flex layer for insulation and protection. Cutouts are made at bonding areas.
Solder Mask & Silkscreen
Solder mask and legends are printed/cured on relevant sections.
Scoring and Routing
Individual boards are cut from panelized sheets. Rigid contours and flex bending lines are defined.
Testing
Electrical testing validates fabrication quality. Automated optical inspection detects defects.
Rigid-Flex PCB Design Rules
Critical rigid-flex design aspects include:
Layer Stack Planning
Define the layer count in rigid and flex sections based on circuit requirements. Ensure adequate flex layers to route interconnections.
Rigid-Flex Transition
Tapered pad shapes and fanout traces are used when routing between rigid and flex layers to compensate for registration tolerance during fabrication.
Flex Bend Radii
The minimum bend radius for flex layers is defined based on dielectric material, copper thickness and layers. Insufficient radius can crack traces.
Component Placement
Place components only on rigid sections. Avoid placement across rigid-flex junctions. Distribute weight evenly.
Board Outline
Define machineable rigid board contours and flex bending lines. Allow tolerance for fabrication capability.
Flex Stiffeners
Add stiffeners made of covers or rigid sections for stabilization along narrow flexible segments. Provides support against flexing stresses.
Thermal Management
Ensure adequate heat dissipation in densely packed rigid sections through thermal vias, copper fills etc.
Assembly Considerations
Assembling components requires special measures:
- Components are only assembled in rigid sections. Flex area is left unpopulated.
- Sufficient clearance should be maintained around component pads close to flex joints.
- Adhesives help strengthen the joint between rigid and flex sections.
- Careful hand soldering is needed near bends to prevent damage from stress.
- Strain relief methods provide support against flex damage during motion.
- Conformal coating increases reliability by preventing moisture ingress through the flexible layers.
- Manual inspection of assembled boards is advised to detect any cracks or breaks.
Cost Impact
Rigid-flex PCBs have a higher fabrication cost compared to conventional rigid boards due to:
- Additional process steps involved
- Specialized materials like adhesives and flexible dielectrics
- Lower panel utilization
- Increased scrap rate
- Manual operations for stacking and lamination
However, the ability to integrate multiple PCBs far outweighs the marginal increase in individual board cost in most applications. Assembly cost reduction also offsets the higher board cost.
For 6 layer rigid-flex PCBs, fabrication cost is approximately 1.8 to 2 times the cost of a similar 6 layer rigid PCB.
Conclusion
6 layer rigid-flex PCB technology provides design flexibility to integrate multiple PCBs interconnected using flexible circuits within a single compact assembly. The combination of standard rigid board fabrication processes and flex circuit manufacturing technologies enables reliable construction of multilayer rigid-flex boards. Careful design planning is needed to effectively utilize the benefits while accounting for assembly and long term reliability. With their ability to package disparate components in close proximity, rigid-flex PCBs offer system level benefits like increased density, reduced weight, faster assembly and improved serviceability. As electronic devices continue getting more compact and complex, the unique value proposition of multilayer rigid-flex PCBs will see them being adopted across industries for a variety of demanding applications.
FAQs
What are some key differences between rigid-flex vs flexible PCBs?
Rigid-flex combines both rigid and flexible circuits. Flex PCBs contain only flexible layers. Rigid-flex provides structural stability with flexibility while flex PCBs are solely meant for dynamic flexing applications.
What design tools are used for rigid-flex PCBs?
Specialized rigid-flex CAD tools like Mentor Xpedition, Altium, Cadence, Zuken are preferred. Separate rigid and flex profiles are generated and then combined.
Can component mounting across both rigid and flex areas be accommodated?
Component mounting on flex areas is not recommended since they cannot withstand soldering stresses and will crack. Components should be mounted only on rigid sections.
How many flex layers are typically used?
2 to 4 flex layers are common for interconnects between rigid sections. If more traces are required, additional flex layers can be added.
What are thermal reliefs in rigid-flex boards?
Thermal reliefs are cutouts below component pads and vias to reduce conducted heat transfer into the flexible region which has lower thermal tolerance.
