Heavy Copper PCB - PCB/PCBA Manufacturer

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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

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

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.

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