PCB Copper Weight: 1oz vs 2oz for Power Applications

Copper weight determines how much current your PCB traces can safely carry and how effectively the board dissipates heat. The standard 1oz copper (35µm thick) works for most signal routing, but power electronics — motor drivers, battery chargers, LED drivers, and power supplies — often demand 2oz (70µm) or heavier copper. This guide helps you choose the right copper weight for your design and understand the manufacturing implications when ordering from Indian and overseas PCB fabricators.

Table of Contents

• Understanding Copper Weight
• Current Carrying Capacity
• Thermal Performance
• Impact on Design Rules
• When to Use 2oz Copper
• Heavy Copper (3oz and Above)
• Cost Considerations
• Frequently Asked Questions

Understanding Copper Weight

Copper weight is expressed in ounces per square foot (oz/ft²), which translates to a specific thickness:

Most Indian PCB fabricators default to 1oz outer and 0.5oz or 1oz inner layers for standard boards. Specifying 2oz copper is a common upgrade that most fabricators support at a moderate price premium.

Current Carrying Capacity

The IPC-2221 standard provides trace width vs current capacity charts. Here are practical values for external (outer) layers with 10°C temperature rise:

Inner layers carry approximately 50% less current than outer layers for the same trace width because they cannot dissipate heat as effectively. Always use the IPC-2221 calculator or Saturn PCB Toolkit for accurate values based on your specific temperature rise allowance.

Thermal Performance

Heavier copper improves thermal conductivity and heat spreading. For power components with exposed thermal pads (QFN, DPAK, TO-252), 2oz copper on the thermal pad layer reduces junction temperature significantly.

• 1oz copper thermal resistance: approximately 70°C/W per square cm
• 2oz copper thermal resistance: approximately 35°C/W per square cm
• Thermal vias under the pad further improve heat transfer to the opposite side

For LED PCBs, motor drivers, and DC-DC converters, the improved thermal performance of 2oz copper often allows you to use a smaller board or fewer heatsink components, potentially offsetting the higher copper cost.

Impact on Design Rules

Heavier copper requires wider minimum trace widths and spacings due to etching limitations:

This means you cannot combine 2oz copper with ultra-fine-pitch components (0.4mm pitch BGA) on the same layer. A common solution is to use different copper weights on different layers: 2oz on the power layers, 1oz on the signal layers. Discuss this with your manufacturer as it affects the lamination process.

When to Use 2oz Copper

Use 2oz copper when any of these conditions apply:

• Continuous current above 2A on traces that must stay narrow (under 2mm)
• Motor driver PCBs: H-bridge outputs, BLDC phase connections
• Battery charger boards: Charging paths for lithium cells above 2A
• LED driver boards: Constant-current paths for high-power LEDs
• Power supply boards: Input and output power paths of DC-DC converters
• Thermal pad connections: For ICs that dissipate more than 1W

For most Arduino shields, sensor breakout boards, and IoT devices, 1oz copper is perfectly adequate.

Heavy Copper (3oz and Above)

Heavy copper PCBs (3-20oz) are used in power electronics, automotive ECUs, and industrial power conversion. They are a niche manufacturing capability.

• 3oz copper: Available from most PCB manufacturers including JLCPCB and PCBWay at significant premium
• 4-6oz copper: Requires specialised fabricators. In India, PCBPower and Shogini Technoarts handle these
• 10oz+ copper: Extreme copper, used in bus bars and high-current distribution. Very few manufacturers worldwide

Heavy copper boards are typically thicker (2.0-3.0mm vs standard 1.6mm) to accommodate the copper thickness and maintain flatness. The cost scales roughly linearly with copper weight — a 3oz board costs approximately 2-3x a 1oz board.

Cost Considerations

At JLCPCB, upgrading from 1oz to 2oz on a 2-layer board adds approximately $2-5 to a standard 5-piece prototype order. For Indian manufacturers, the premium is similar in percentage terms but the base price is higher.

Frequently Asked Questions

Can I have different copper weights on different layers?

Yes, mixed copper weights are common. A typical power PCB uses 2oz on outer layers (power paths and thermal pads) and 1oz on inner layers (signal routing). Specify this in your stack-up drawing. Most fabricators support this at no additional premium beyond the heavier copper cost.

Does heavier copper affect soldering?

Yes, heavier copper acts as a larger heat sink, making hand soldering more difficult. Pads on 2oz copper require higher iron temperature (370-380°C vs 320-340°C) and longer dwell time. For assembly houses using reflow ovens, the reflow profile may need adjustment to ensure all joints reach adequate temperature.

How do I calculate the trace width I need?

Use the Saturn PCB Toolkit (free) or the IPC-2221 trace width calculator. Input: required current, acceptable temperature rise (10°C is common), copper weight, and whether the trace is on an outer or inner layer. The calculator gives you the minimum trace width. Always add margin — use at least 25% wider traces than the calculated minimum.

Is 2oz copper necessary for a 5V 2A USB power delivery board?

Not necessarily. At 2A, a 1oz copper trace of 1.0mm width on an outer layer handles the current with about 10°C temperature rise. If your layout permits traces this wide, 1oz is sufficient. However, if space constraints force narrow traces (under 0.5mm), then 2oz copper provides more headroom.

What about copper pour (polygon fill) instead of wider traces?

Copper pour is an excellent way to increase current capacity without using heavier copper. A solid copper pour on 1oz copper carries far more current than a single trace. For power planes, always use copper pour connected to the power net. Combine copper pour with multiple vias for layer transitions.

Find copper clad boards, prototyping PCBs, and soldering equipment for your power electronics projects at Zbotic PCB & Prototyping — fast delivery across India.