Heavy Copper PCB Manufacturing and Design Guidelines
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Introduction
Heavy copper PCBs refer to boards with copper thickness exceeding 2 oz (70 μm). The thicker copper provides advantages like higher current carrying capacity, better thermal performance, and reliability. However, manufacturing these boards requires specialized capabilities.
This article provides an overview of heavy copper PCB technology, benefits, manufacturing processes, and key design considerations when working with PCB fabricators.
What is Heavy Copper PCB?
Heavy copper PCBs are defined as boards with:
- Copper thickness > 2 oz (70 μm)
- Preferred term over “thick” copper PCB
Common heavy copper weights:
- 2 oz (70 μm)
- 3 oz (105 μm)
- 4 oz (140 μm)
- 6 oz (210 μm)
- 8 oz (280 μm)
- 10 oz (350 μm)
Other key attributes:
- Typically compatible with FR-4 dielectric
- Mostly used for inner layers rather than outer layers
- Plated through holes (PTHs) often need to be plugged/filled
- Requires careful registration and lamination
Heavy copper inner layers improve thermal performance and current carrying capacity useful for applications like LED lighting, power electronics, and electric vehicle inverters.
8 Layer PCB Inner 8oz, 20 oz Out layer
Benefits of Heavy Copper PCBs
Heavy copper PCBs provide several benefits compared to standard 1 oz copper:
Higher Current Capacity
Thick copper lowers current density levels. This reduces heating and allows larger current handling without damage.
Improved Thermal Performance
The thicker copper acts as a heat spreader due to higher thermal conductivity. This keeps components cooler.
Lower Resistance
Thicker copper layers lead to lower sheet resistance. This improves conductivity and reduces resistive losses.
Better Power Distribution
Thick copper inner planes serve as ideal power distribution layers in multilayer PCBs. They minimize ground bounce and supply noise.
Higher Reliability
Thicker copper is more resistant to thermal stress, fatigue, and damage from repeated electrical loads. This enhances long term reliability.
EMI and Noise Shielding
Thick copper layers embedded within the PCB provide shielding against electromagnetic interference and crosstalk.
Heavy Copper PCB Manufacturing Overview
Producing heavy copper PCBs requires specialized fabrication processes and equipment considerations compared to standard PCBs.
Sourcing Copper Clad Laminates
The raw material is FR-4 laminates clad with rolled copper foils. Popular weights:
- 1⁄2 oz (18 μm)
- 1 oz (35 μm)
- 2 oz (70 μm)
- 3 oz (105 μm)
Copper foils are bonded to dielectric cores like FR-4, CE resin, hydrocarbon, ceramic, Teflon using adhesive or fusion bonding.
Registration and Layup
Aligning layers during layup is critical due to thick copper tolerance issues (±10% for 2 oz copper). Automatic optical registration systems enable precision alignment.
Lamination
Thick copper requires higher lamination pressure, temperature, and time compared to standard PCBs. This ensures strong adhesion between copper and dielectric.
Typical lamination parameters for heavy copper PCBs:
| Copper Thickness | Pressure | Temperature | Time |
|---|---|---|---|
| 1 oz | 300 PSI | 180°C | 60 min |
| 2 oz | 350 PSI | 185°C | 75 min |
| 4 oz | 400 PSI | 190°C | 90 min |
Plated Through Holes
PTHs need to be plugged/filled to avoid trapped gases and delamination issues during lamination. Filling options:
- Plated copper fills
- Conductive pastes
- Non-conductive epoxy plugs
Etching
Thick copper requires longer etch times. Panel agitation helps improve etch uniformity. Etch masks may also need to be thicker for prolonged etching.
Pillar Plating
After etching, additional copper is plated to build thicker connection pillars around pads and vias. This compensates for copper loss during etching.
AOI Inspection
Heavy copper layers make visual inspection difficult. Automated optical inspection is essential to check alignment, defects, and COPV separation.
Testing and Certification
Electrical testing validates connectivity and continuity. IPC 6012 Class 3 certification is recommended for high reliability heavy copper PCBs.
Heavy Copper PCB Design Guidelines
Below are some key design considerations for heavy copper PCBs:
Layer Stacking
- Position thick copper layers close to the board center to minimize warpage.
- Do not place outer layers next to each other as it exacerbates registration issues.
- Rotate fiber weave direction 90° between adjacent dielectric layers for stability.
Component Placement
- Ensure sufficient clearance from plane layers for soldermask coverage.
- Account for component shadows falling on inner copper layers.
- Check for exposed copper at drilled holes.
Thermal Management
- Place heat generating components over thick copper layers to act as heat spreaders.
- Provide multiple vias beneath hot components to transfer heat to inner planes.
High Current Traces
- Use copper pouring/polygons for high current lines instead of routing multiple parallel traces.
- Place adjacent to plated thru-hole vias for heat dissipation.
Filled Vias
- Limit use of filled vias as they impair heat transfer compared to hollow vias.
- Countersink filled vias and keep soldermask clear of holes.
Panel and Tooling
- Allow generous tolerances for fabrication and assembly.
- Account for material shrinkage, stretching, and warpage.
- Use fiducials and test coupons on panel for easy tooling.
DFM Analysis
- Seek DFM feedback from fabricator during design phase.
- Check manufacturability, especially around heavy copper tolerance issues.
Early engagement with the PCB manufacturer smooths the design process and avoids issues during prototyping.
Finding the Right Heavy Copper Partner
When selecting a PCB manufacturer for heavy copper boards, ensure they meet the following criteria:
Capabilities Checklist
- Available laminate thicknesses – 2 oz, 3 oz, 4 oz, etc.
- PTH filling – Copper, conductive ink, epoxy plugging
- Registration accuracy – ≤ 0.003” preferred
- Fine line etching – ≤ 4 mil line/space
- Plating thickness – ≥ 2.5 mils copper in holes
- Sectional plating to fill gaps post-etch
- AOI inspection – 5+ camera high resolution
Quality and Certifications
- IPC 6012 Class 3 shop floor processes
- ISO 9001 certified
- UL or TUV approved facility
- Qualification testing – thermal stress, shock, vibration
Technical Expertise
- Experience with heavy copper designs – review references
- Design for manufacturing (DFM) support
- Thermal analysis and plane current simulations
- Feedback on layout, stack up, and reliability
Lean Prototyping
- Low NRE charges
- No minimum quantity requirements
- Small panel or array formats
- 24 hour turnaround for simple 2-4 layer builds
Evaluate manufacturers thoroughly on these aspects before choosing your heavy copper PCB partner.
Conclusion
Heavy copper PCB technology enables applications with high current loads, thermal performance demands, and power integrity requirements. The thick copper layers offer reliability enhancements but also necessitate tight process controls during fabrication. Working closely with the PCB manufacturer during the design stage and following layout guidelines helps realize the benefits of heavy copper PCBs in your product. As heavy copper fabrication requires specialized precision and expertise, partnering with an established manufacturer that provides design reviews and qualification testing delivers the optimal outcome.
FAQ
What are the key benefits of using heavy copper PCBs?
Heavy copper PCBs offer higher current capacity, better thermal conductivity, lower electrical resistance, enhanced power distribution, and improved reliability compared to standard 1 oz copper boards.
What PCB characteristics help identify a board as heavy copper?
Key indicators of heavy copper PCBs are copper thickness over 2 oz (70 μm), plated through holes being plugged or filled, and typically used only for inner layers rather than outer layers.
What are the typical applications suited for heavy copper PCBs?
Heavy copper boards are commonly used in high power electronics like motor drives, power supplies, battery chargers, LED lighting, energy storage, and electric vehicle inverters.
What are the special considerations when soldering heavy copper PCBs?
Thick copper requires higher soldering temperature and longer dwell time for heat to soak through to bond properly. Also important to account for thermal expansion and mechanical stress on solder joints.
How does the cost of heavy copper PCBs compare to standard copper thickness?
The cost of heavy copper PCBs can be 50% to 100% higher than equivalent standard copper thickness boards due to more expensive materials, specialized fabrication processes, lower yields, and higher scrap rates.