Introduction
Heavy copper PCBs are specialized circuit boards featuring copper thicknesses exceeding 2 oz (70 μm). This increased copper thickness offers several distinct advantages including enhanced current carrying capacity, superior thermal management, and heightened reliability. These attributes make heavy copper PCBs indispensable in applications requiring robust electrical performance and resilience under demanding conditions.
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Rigid-flex PCB
What is Heavy Copper PCB?
Heavy copper PCBs refer to circuit boards with copper thickness exceeding 2 oz (70 μm), preferred over the term "thick" copper PCB. They are available in various standard weights:
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2 oz (70 μm)
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3 oz (105 μm)
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4 oz (140 μm)
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6 oz (210 μm)
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8 oz (280 μm)
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10 oz (350 μm)
Key Attributes:
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Typically use FR-4 dielectric material
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Primarily utilized for inner layers rather than outer layers
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Plated through holes (PTHs) often require plugging or filling
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Requires precise registration and lamination processes
Heavy copper PCBs enhance:
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Thermal performance
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Current carrying capacity
Applications:
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LED lighting
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Power electronics
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Electric vehicle inverters
These attributes make heavy copper PCBs indispensable in applications requiring robust thermal management and high current capabilities.
Benefits of Heavy Copper PCBs
Heavy copper PCBs offer significant advantages over standard 1 oz copper:
Higher Current Capacity: Thick copper reduces current density, lowering heating and enabling higher current handling capabilities.
Improved Thermal Performance: Enhanced heat spreading due to higher thermal conductivity of thick copper keeps components cooler.
Lower Resistance: Thicker copper layers reduce sheet resistance, enhancing conductivity and minimizing resistive losses.
Effective Power Distribution: Thick copper inner layers serve as robust power distribution planes in multilayer PCBs, reducing ground bounce and noise.
Enhanced Reliability: Greater resistance to thermal stress, fatigue, and electrical load damage improves long-term reliability.
EMI and Noise Shielding: Embedded thick copper layers provide effective shielding against electromagnetic interference and crosstalk.
These attributes make heavy copper PCBs essential for applications requiring high reliability, thermal management, and electrical performance.
Heavy Copper PCB Manufacturing Overview
Producing heavy copper PCBs involves specialized fabrication processes and equipment tailored for their unique requirements compared to standard PCBs.
Sourcing Copper Clad Laminates
Heavy copper PCBs start with FR-4 laminates clad with rolled copper foils of various weights:
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1⁄2 oz (18 μm)
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1 oz (35 μm)
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2 oz (70 μm)
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3 oz (105 μm)
Copper foils are bonded to dielectric cores such as FR-4, CE resin, hydrocarbon, ceramic, and Teflon using adhesive or fusion bonding methods.
Registration and Layup
Precise alignment of layers during layup is critical due to thick copper tolerance issues (±10% for 2 oz copper). Automatic optical registration systems ensure accurate alignment.
Lamination
Laminating heavy copper requires higher pressure, temperature, and time compared to standard PCBs to ensure strong adhesion between copper and dielectric materials.
Plated Through Holes (PTHs)
PTHs in heavy copper PCBs require filling or plugging to prevent trapped gases and delamination during lamination. Filling options include plated copper fills, conductive pastes, and non-conductive epoxy plugs.
Etching
Etching thick copper layers requires longer times. Agitation during panel etching improves uniformity, and thicker etch masks are often necessary for extended etching durations.
Pillar Plating
After etching, additional copper is plated to form thicker connection pillars around pads and vias, compensating for copper loss during the etching process.
Automated Optical Inspection (AOI)
Visual inspection of heavy copper layers is challenging. AOI systems are crucial for inspecting alignment, detecting defects, and ensuring clearance of Copper Over Plating Void (COPV).
Testing and Certification
Electrical testing validates connectivity and continuity, with IPC 6012 Class 3 certification recommended for ensuring high reliability of heavy copper PCBs.
Heavy Copper PCB Design Guidelines
Key Design Considerations for Heavy Copper PCBs:
Layer Stacking:
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Position thick copper layers near the board center to minimize warping.
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Avoid placing outer layers adjacent to each other to mitigate registration challenges.
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Rotate fiber weave direction by 90° between adjacent dielectric layers for enhanced dimensional stability.
Component Placement:
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Ensure adequate clearance from plane layers to ensure complete soldermask coverage.
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Consider shadows cast by components onto inner copper layers.
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Verify for exposed copper at drilled holes to prevent unintended electrical connections.
Thermal Management:
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Position heat-generating components over thick copper layers to utilize them as heat spreaders.
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Utilize multiple vias beneath hot components to efficiently transfer heat to inner planes.
High Current Traces:
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Use copper pouring or polygons for high current lines instead of multiple parallel traces.
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Place these traces adjacent to plated through-hole vias to facilitate effective heat dissipation.
Filled Vias:
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Minimize the use of filled vias as they can impede heat transfer compared to hollow vias.
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If necessary, countersink filled vias and ensure soldermask clearance around the holes.
Panel and Tooling:
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Incorporate generous tolerances for fabrication and assembly processes.
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Account for material shrinkage, stretching, and potential warping during manufacturing.
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Include fiducials and test coupons on panels to facilitate precise tooling and testing.
DFM Analysis:
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Seek Design for Manufacturing (DFM) feedback from the fabricator during the design phase.
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Address manufacturability concerns, particularly regarding heavy copper tolerance issues.
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Early collaboration with the PCB manufacturer ensures smoother prototyping and production phases.
Finding the Right Heavy Copper Partner
Selecting a PCB Manufacturer for Heavy Copper Boards:
Capabilities Checklist:
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Laminate Thicknesses: Ensure capabilities for 2 oz, 3 oz, 4 oz, etc., copper thicknesses.
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PTH Filling: Capability with options such as copper, conductive ink, or epoxy plugging for plated through-holes.
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Registration Accuracy: Precision of ≤ 0.003” (preferred) for accurate layer alignment.
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Fine Line Etching: Ability to achieve ≤ 4 mil line/space for intricate circuit designs.
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Plating Thickness: Minimum plating thickness of ≥ 2.5 mils copper in holes for robust connectivity.
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Sectional Plating: Capability for post-etch plating to fill gaps and ensure uniform copper distribution.
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AOI Inspection: Utilization of 5+ camera high-resolution automated optical inspection for quality assurance.
Quality and Certifications:
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IPC 6012 Class 3 Standards: Adherence to stringent IPC 6012 Class 3 shop floor processes.
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ISO 9001 Certification: Certified quality management system ensuring consistent manufacturing standards.
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UL or TUV Approval: Compliance with UL or TUV safety and performance standards.
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Qualification Testing: Experience in thermal stress, shock, and vibration testing to ensure reliability and durability.
Technical Expertise:
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Experience with Heavy Copper Designs: Demonstrated expertise with references in handling heavy copper PCB projects.
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Design for Manufacturing (DFM) Support: Capability to provide comprehensive DFM feedback and optimization.
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Thermal Analysis and Plane Current Simulations: Proficiency in thermal management and electrical current simulations for optimal performance.
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Feedback and Consultation: Ability to provide insights on layout, stack-up, and reliability enhancements.
Lean Prototyping:
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Low NRE Charges: Cost-effective prototyping with minimal Non-Recurring Engineering (NRE) charges.
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No Minimum Quantity Requirements: Flexible production capabilities accommodating both small and large volume orders.
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Quick Turnaround: Expedited services with 24-hour turnaround for simple 2-4 layer builds.
Evaluation Considerations:
Thoroughly assess potential manufacturers based on these criteria to ensure they meet your requirements for heavy copper PCB fabrication.
Conclusion
Heavy copper PCB technology addresses high current loads, thermal performance needs, and power integrity requirements in electronic applications. Thick copper layers enhance reliability but demand meticulous process controls during fabrication. Collaboration with a PCB manufacturer early in the design phase and adherence to layout guidelines are crucial to harnessing the advantages of heavy copper PCBs effectively. Partnering with an experienced manufacturer offering design reviews and qualification testing ensures optimal outcomes in heavy copper PCB fabrication, leveraging specialized precision and expertise.