1oz vs 2oz Copper PCB: When to Upgrade and What It Actually Costs

After manufacturing thousands of boards at both copper weights, here's what we've learned about when 2oz copper actually pays for itself — and when it just adds cost and restricts your routing.

The Quick Decision

If any trace needs to carry more than 1A at your minimum trace width, or thermal spreading from copper planes is critical to your design, go 2oz on those layers. If your board is primarily signal routing with power delivered through wide pours and planes, stay at 1oz and save 15-25% on your board cost.

Current Capacity: The Real Numbers (IPC-2152)

Values at 10°C temperature rise above ambient.

Key insight: 2oz gives you ~40-50% more current capacity, not double. The relationship isn't linear because heat dissipation changes with copper volume.

Manufacturing Impact You Need to Know

Here's what most guides miss: going to 2oz copper changes your design rules.

Minimum trace/space at 2oz: 5/5mil (vs 3.5/3.5mil at 1oz)

Why? Etching 70µm of copper takes twice as long as 35µm. During that time, lateral etching (undercut) proceeds continuously, removing ~20-25µm from each side vs ~10-15µm at 1oz. The manufacturer applies etch compensation on the phototool, but there's a physical limit to how narrow a trace can survive the extended etch.

The etch factor (vertical:lateral ratio) goes from ~2.5:1 at 1oz to ~3:1 at 2oz. This directly determines your achievable minimum geometry.

Impedance Changes (This Catches People)

Thicker copper means wider traces for the same impedance. For a 50Ω microstrip with 4mil dielectric to ground:

• 1oz (35µm): ~4.2mil trace width
• 2oz (70µm): ~5.8mil trace width

That's a 40% increase. For differential pairs, both trace AND spacing increase, which significantly impacts routing density. If you need both high current AND controlled impedance, use mixed copper weights: 2oz on power layers, 0.5-1oz on signal layers.

Real Cost Difference

For a 100×100mm, 6-layer board with ENIG finish:

The cost premium comes from: longer etch time (reduced line throughput), etch compensation CAM work, and 2-3% lower first-pass yield at 2oz inner layers.

Decision Matrix by Application

DFM Rules for 2oz Designs

1. Min trace/space: 5/5mil (not 4/4)
2. Annular ring: 4.5-5mil (vs 3.5mil at 1oz)
3. Solder mask dam: 4mil minimum (vs 3mil)
4. Copper balance: Keep within 20% fill variation between layers
5. Mixed weights work: Use 0.5oz inner for signals, 2oz outer for power

The golden rule: never let power requirements force your signal traces wider than optimal for impedance control. Separate power and signal onto different layers with appropriate copper weights for each function.

Based on production data from our advanced multilayer facility. For copper weight recommendations for your specific design, visit atlaspcb.com/get-quote.

Further reading:

• PCB Copper Weight and Thickness Guide
• Heavy Copper PCB for Power Electronics
• PCB Trace Width Current Capacity