Conductor Loss Calculator | Skin Effect & Resistance

What Is Conductor Loss in an RF PCB Trace?

Conductor loss is the signal attenuation caused by resistive heating in the metal traces and reference planes of a PCB transmission line. At RF and microwave frequencies the skin effect forces current into a thin surface layer of the conductor, raising its effective resistance far above the DC value. For a 50 Ω microstrip on 1 oz (35 µm) copper at 10 GHz, conductor loss typically accounts for 0.02–0.06 dB/cm—often comparable to or exceeding dielectric loss, depending on the laminate chosen.

Why Conductor Loss Matters at High Frequencies

At DC, current distributes uniformly across the full cross-section of a trace. As frequency rises, electromagnetic fields push current toward the conductor surfaces. The depth at which current density falls to 1/e (about 37 %) of its surface value is the skin depth δ. For copper (σ ≈ 5.8 × 10⁷ S/m) at a few representative frequencies:

At 10 GHz the skin depth is only 0.66 µm—far thinner than standard 1 oz copper (35 µm). Current flows in a thin shell, so the effective conductor cross-section shrinks and resistance climbs with the square root of frequency. Use the skin depth calculator to check the value for your operating frequency and conductor material. You can also try the interactive tool below.

If you enter 10 GHz and copper’s conductivity of 5.8 × 10⁷ S/m, the result is approximately 0.66 µm. That tells you the effective conducting layer is less than 2 % of a half-ounce foil’s thickness—confirming that trace geometry, not bulk copper weight, dominates loss at this frequency.

Conductor Loss Formula

For a microstrip line the conductor attenuation constant α_c (in Np/m) is commonly expressed as:

α_c = R_s / (Z₀ · w)

where R_s = √(π f μ₀ / σ) is the surface resistivity of the conductor (Ω/□), Z₀ is the characteristic impedance, and w is the trace width. Converting to dB per unit length: α_c (dB/m) = 8.686 × α_c (Np/m).

Key observations from this relationship:

• Loss rises with √f—doubling the frequency increases conductor loss by about 41 %.
• Wider traces reduce loss because current spreads over a larger perimeter.
• Lower-impedance lines (wider w, thinner dielectric) tend to have lower conductor loss, all else being equal.
• Higher-conductivity metals (copper vs. nickel) directly lower R_s.

This simplified model assumes smooth copper. Real foils have surface roughness that further increases loss, especially above a few GHz. To quantify that additional penalty, run your numbers through a copper roughness loss calculator using the Huray or Hammerstad–Jensen correction.

Interactive Conductor Loss Calculator

Enter your trace width, copper thickness, conductor conductivity, frequency, and line impedance to get conductor attenuation in dB per unit length.

For example, a 50 Ω microstrip with a 0.30 mm (about 12 mil) wide trace on 1 oz copper at 5 GHz returns roughly 0.025 dB/cm. Over a 10 cm feed network that totals 0.25 dB—significant in a low-noise receiver front end. If the result is too high for your link budget, consider widening the trace (which may require a thicker dielectric to hold 50 Ω), switching to stripline for better current distribution on both reference planes, or selecting an attenuator pad calculator to verify that your gain budget still closes after accounting for this loss.

Practical Ways to Reduce Conductor Loss

Choose the Right Copper Weight and Finish

Because current travels only in the outermost skin depths, plating finish matters more than bulk copper weight above a few GHz. ENIG adds a thin nickel barrier (σ ≈ 1.4 × 10⁷ S/m—about 4× lower than copper), which can increase conductor loss noticeably at millimeter-wave frequencies. Immersion silver or OSP preserves the copper surface conductivity. Rogers RO4350B datasheets specify loss tangent but remind designers that total insertion loss also depends on copper roughness and surface finish.

Minimize Roughness

Standard electrodeposited (ED) copper foils have an RMS roughness of 1.5–2.5 µm. At 10 GHz, where skin depth is 0.66 µm, that roughness is several times δ and can add 30–50 % to the smooth-copper conductor loss. Specify low-profile (LP) or very-low-profile (VLP) foil—typically ≤ 1.0 µm RMS—for any design above 5 GHz.

Widen Traces Where Layout Allows

A wider conductor spreads current over more surface area. If impedance must stay at 50 Ω, increase the dielectric thickness proportionally. Thicker cores also reduce the percentage of current that flows on the rough bottom side of the trace.

Use Stripline for Long Runs

Stripline has two reference planes, so return current splits between them and the effective loop resistance drops. The trade-off is tighter fabrication tolerances and the need for via transitions at component pads.

Conductor Loss vs. Dielectric Loss: Which Dominates?

Dielectric loss scales linearly with frequency (proportional to f × tan δ), while conductor loss scales with √f. At low-GHz frequencies on a high-loss laminate like FR-4 (tan δ ≈ 0.020), dielectric loss usually dominates. On low-loss laminates such as RO4350B (tan δ ≈ 0.0037) or PTFE-based RO3003 (tan δ ≈ 0.0013), conductor loss can be the larger contributor up into the tens of GHz, especially with rough copper. A complete loss budget should sum both terms—and add the roughness correction—before comparing against the system’s allowable insertion loss.

FAQ

What is a typical conductor loss for a 50 Ω microstrip at 10 GHz?

On 1 oz smooth copper with a low-loss laminate, expect roughly 0.03–0.06 dB/cm depending on trace width, roughness, and surface finish. Roughness alone can push the value toward the higher end.

Does copper weight affect conductor loss at RF?

Above a few hundred MHz the skin depth is much thinner than even half-ounce foil (17.5 µm), so adding copper weight has negligible effect. Surface roughness and plating finish matter far more.

How does ENIG finish increase conductor loss?

The 3–6 µm nickel layer in ENIG has about one-quarter the conductivity of copper. Because current flows in the outermost skin depths, nickel’s higher resistivity raises R_s and can add 0.01–0.03 dB/cm at millimeter-wave frequencies. Immersion silver avoids this penalty.

Can I reduce conductor loss by using gold plating?

Gold’s conductivity (4.1 × 10⁷ S/m) is lower than copper’s (5.8 × 10⁷ S/m), so a thick gold layer actually increases loss slightly. A thin flash gold over copper for bondability is acceptable, but avoid thick electrolytic gold on signal traces above 5 GHz.