When optimizing PCB copper thickness reduction for a thick copper board, many engineers evaluate current-carrying capability mainly according to DC current and conventional IPC-based calculations. However, this approach may not fully represent the thermal behavior of high-frequency power circuits.

In switching power supplies, inverters, motor drives, and other power-conversion systems, the current waveform may contain a significant high-frequency component in addition to its DC component. As frequency increases, the distribution of current within the copper conductor changes because of the skin effect and, in some structures, the proximity effect. These effects can increase AC resistance and associated losses.

As a result, a PCB may pass a conventional DC temperature-rise calculation but still develop localized hot spots during actual switching operation.

For PCB copper thickness reduction, engineers therefore need to distinguish between predominantly DC current paths and high-frequency switching paths. Copper thickness, trace width, loop geometry, ripple current, copper distribution, and thermal management should be evaluated together rather than relying on copper thickness alone.

1. How the Skin Effect Influences Thick Copper PCB Current-Capacity Evaluation

The skin effect describes the tendency of alternating current to become increasingly concentrated toward the surface of a conductor as frequency increases. The characteristic penetration depth, commonly referred to as skin depth, decreases approximately with the inverse square root of frequency.

For copper, the skin depth is approximately:

• 0.21 mm at 100 kHz
• 0.066 mm at 1 MHz
• 0.021 mm at 10 MHz

These values are approximate and assume idealized conditions. Actual AC resistance in a PCB structure can also be influenced by conductor geometry, nearby copper, trace spacing, current return paths, and proximity effects.

Consider a PCB with approximately 2 oz copper, corresponding to about 70 μm of copper thickness. At 100 kHz, the copper thickness is smaller than the approximate skin depth, so a substantial portion of the conductor cross-section can still contribute to current conduction.

At 1 MHz, however, the skin depth is approximately 66 μm, which is close to the thickness of 2 oz copper. Increasing copper thickness beyond this point does not necessarily provide the same proportional reduction in AC resistance as it would under a purely DC condition.

This is an important consideration for PCB copper thickness reduction. The benefit of increasing copper thickness depends not only on current magnitude but also on the frequency spectrum of the current waveform.

For example, a switching converter may have a large DC bus current but also contain switching-frequency ripple and higher-order harmonics. The total copper loss can therefore be viewed conceptually as the combination of DC conduction loss and frequency-dependent AC loss.

The higher-frequency components may contribute disproportionately to localized heating, particularly in compact switching loops where current density is concentrated.

2. DC Current and Ripple Current Require Different Evaluation Methods

A power PCB should not necessarily be evaluated as one uniform electrical structure. Different current paths may have very different requirements.

DC Bus and Low-Ripple Power Paths

A DC bus with relatively low ripple is primarily dominated by resistive conduction loss. In this case, engineers can use conventional current-capacity calculations together with thermal simulation to evaluate whether copper thickness can be reduced.

Increasing trace width or using larger copper areas can compensate for some of the loss of conductor cross-sectional area.

However, the evaluation should still consider trace length, ambient temperature, thermal spreading, copper distribution, vias, component connections, and the allowable temperature rise.

High-Frequency Switching Power Loops

The situation is different for a high-frequency power loop.

A switching loop may carry rapidly changing current with substantial high-frequency components. In addition to DC resistance, engineers should consider AC resistance, parasitic inductance, current-loop area, switching frequency, harmonic content, and the interaction between adjacent conductors.

Simply increasing trace width may not solve every problem. A physically wide but electrically long switching loop can still have excessive parasitic inductance and electromagnetic radiation.

For these circuits, reducing loop area and minimizing the distance between switching devices, capacitors, and their associated return paths can be as important as selecting copper thickness.

Low-Current Signal Circuits

Low-current control, sensing, and communication circuits generally have much lower current-carrying requirements than power paths. In many applications, standard copper thickness can therefore be sufficient.

This creates an opportunity for regional copper optimization rather than applying the same heavy-copper specification to the entire PCB.

3. Ripple Current and AC Losses in Switching Circuits

Ripple current is one of the most important factors to consider when reducing copper thickness in high-frequency power circuits.

The total current waveform can contain a DC component plus periodic or transient AC components. The magnitude and frequency spectrum of these components depend on the converter topology, switching frequency, control strategy, inductor characteristics, capacitor selection, operating point, and load conditions.

As the AC component increases, frequency-dependent conductor losses can become more significant.

The relationship between AC loss and current is particularly important because conductor power loss increases approximately with the square of current. Therefore, reducing unnecessary ripple current can improve thermal performance without simply adding more copper.

This means that copper-thickness optimization should not be treated as a material-only optimization.

Engineers should also investigate whether the circuit itself can be optimized to reduce high-frequency current circulation.

Potential measures include:

• Placing high-frequency decoupling capacitors close to switching devices
• Optimizing power-stage capacitor selection
• Reducing unnecessary parasitic inductance
• Shortening high-current switching paths
• Minimizing switching-loop area
• Improving current return-path continuity
• Reviewing the placement of inductors, MOSFETs, diodes, and capacitors
• Evaluating the ripple-current spectrum under different load conditions

When ripple current is reduced at the circuit level, AC conduction losses can also decrease, potentially creating additional design margin for copper-thickness optimization.

4. PCB Layout Optimization Can Be More Effective Than Simply Adding Copper

One common mistake in heavy-copper PCB design is assuming that increasing copper thickness is always the most effective way to reduce power loss.

For high-frequency circuits, PCB design should address both electrical resistance and parasitic effects.

The physical loop should be as compact as practical. Switching devices and high-frequency capacitors should be positioned so that the forward and return paths remain close together.

Long traces increase resistance and can also increase parasitic inductance. A shorter current path therefore helps reduce both conduction loss and high-frequency loop inductance.

The reference and return paths should also be examined carefully. An apparently short signal or power trace may still have a poor return path if the corresponding reference plane is interrupted.

For multilayer boards, parallel copper paths can sometimes be used to distribute current between layers. For example, top and bottom copper layers may share current through an appropriately designed via structure.

However, simply connecting two copper layers with a few vias does not guarantee uniform current sharing. Via quantity, via diameter, placement, connection geometry, current distribution, and thermal conditions should all be considered.

5. Optimize Copper Thickness by Circuit Region

A more practical approach is to divide the PCB into functional current regions instead of applying one copper-thickness specification to the entire board.

For example:

This regional strategy can reduce unnecessary heavy-copper processing in low-current areas while preserving appropriate copper capacity in critical power regions.

For PCB copper thickness reduction, the goal is therefore not necessarily to reduce copper thickness everywhere. Instead, engineers should determine where heavy copper is electrically necessary and where standard copper can meet the requirements.

This can also simplify manufacturing and improve routing flexibility.

6. Thermal Testing Must Include Actual Switching Conditions

Simulation is an important part of copper optimization, but prototype testing remains essential.

The prototype should be tested under both steady-state and dynamic operating conditions. A simple DC load test may not reproduce the actual current waveform of a switching power circuit.

Thermal testing should therefore include:

• Full-load steady-state operation
• Different load levels
• Load-step testing
• Startup and shutdown conditions
• Switching-frequency operation
• Maximum expected ambient temperature
• Thermal imaging
• DC resistance measurement
• Ripple-current measurement
• Critical component temperature measurement

During thermal testing, engineers should use thermal imaging to identify localized hot spots around MOSFETs, diodes, inductors, capacitors, vias, connectors, and narrow copper transitions.

It is also useful to compare the original thick-copper design with the optimized design under identical test conditions.

The comparison should include not only the maximum temperature but also the location of the hot spot, temperature distribution, voltage drop, resistance, and power loss.

A board that shows acceptable average temperature can still have a localized hot spot caused by current concentration or an unfavorable switching-loop layout.

7. Measure Ripple and AC Loss Instead of Relying Only on Temperature

Temperature is the final result of multiple loss mechanisms. It does not always reveal the underlying cause.

When a prototype shows unexpected heating, engineers should measure the electrical conditions that produce the heat.

Important measurements include:

• Switching waveform
• Ripple-current amplitude
• Switching frequency
• Harmonic content where relevant
• Voltage overshoot and ringing
• DC voltage drop
• Conductor resistance
• Component losses
• Temperature distribution

Oscilloscope measurements with appropriate current probes can help characterize the actual switching waveform.

For more demanding designs, frequency-domain analysis or electromagnetic simulation may be useful to estimate frequency-dependent conductor behavior.

The purpose is to determine whether the temperature increase comes mainly from DC conduction loss, high-frequency AC loss, component loss, switching loss, or a combination of several mechanisms.

This distinction is particularly important when implementing PCB copper thickness reduction. If the dominant loss is switching loss in a semiconductor device, simply increasing copper thickness may provide limited improvement. If the dominant loss is conductor resistance, trace geometry and copper cross-section become more important.

8. Reliability Verification After Copper Thickness Reduction

After electrical and thermal prototype testing, the optimized PCB should undergo an appropriate reliability validation program.

Long-duration operation can expose degradation mechanisms that are not visible during short-term testing.

Depending on the application, the reliability program may include:

• Long-duration full-load operation
• Temperature cycling
• High-temperature aging
• Damp-heat testing
• Repeated load cycling
• Electrical insulation testing
• Post-aging resistance measurement
• Post-aging thermal testing

Before and after reliability testing, engineers should compare conductor resistance and temperature rise at defined operating points.

For high-power products, repeated thermal cycling can also place stress on solder joints, vias, component connections, and PCB materials. Therefore, the reliability assessment should cover the complete current path rather than focusing only on copper thickness.

A successful optimization should demonstrate that the reduced-copper design retains sufficient electrical and thermal margin after the required environmental and operating stresses.

9. Practical Copper-Thickness Optimization Strategy for Power PCBs

A reliable optimization workflow can be summarized as:

Current Requirement Analysis → DC/AC Current Separation → Ripple Analysis → Thermal and Electrical Simulation → PCB Design Optimization → DFM Review → Prototype Fabrication → Switching-Condition Testing → Thermal Testing → Reliability Validation → Mass-Production Control

During the analysis stage, engineers should first determine which current paths are dominated by DC current and which contain significant high-frequency components.

Next, the current waveform and ripple spectrum should be evaluated. This helps determine whether copper thickness, trace width, loop geometry, or circuit-level optimization should be prioritized.

The design can then be modified according to the characteristics of each circuit region.

Before mass production, the optimized PCB should pass both electrical and thermal validation under representative operating conditions.

For production, Kingda can incorporate the approved copper specification, trace geometry, plating requirements, and critical inspection items into the manufacturing control process.

10. Key Considerations for Kingda Thick Copper PCB Projects

For a thick copper PCB project, copper thickness should be selected according to the complete electrical operating environment rather than current magnitude alone.

Important factors include:

• DC current
• Ripple current
• Switching frequency
• Harmonic content
• Trace width and length
• Copper thickness
• Current-loop area
• Via structure
• Thermal environment
• Component power dissipation
• PCB layer configuration
• Manufacturing capability

Kingda can support copper-thickness optimization by evaluating PCB fabrication requirements together with layout and manufacturing considerations.

The objective is to identify a copper configuration that provides sufficient current capacity and thermal margin without unnecessarily increasing material usage or manufacturing complexity.

For high-frequency power boards, the best optimization result may come from combining moderate copper thickness with wider conductors, shorter current paths, improved capacitor placement, parallel copper layers, and optimized switching-loop geometry.

Conclusion

The skin effect and ripple current introduce important constraints when reducing copper thickness in high-frequency power PCBs.

Conventional DC current calculations remain useful for predominantly DC power paths, but they may not fully capture the behavior of switching circuits with substantial high-frequency current components.

For reliable PCB copper thickness reduction, engineers should separate DC and AC current paths, analyze the current waveform, evaluate frequency-dependent losses, optimize switching-loop geometry, reduce unnecessary ripple current, and validate the final design through prototype and reliability testing.

The key principle is simple: copper thickness should be optimized together with current distribution, frequency, trace geometry, thermal management, and circuit topology.

By combining simulation, PCB design optimization, prototype thermal testing, electrical measurements, and long-term reliability validation, engineers can reduce unnecessary copper usage while maintaining the performance and reliability required for demanding power-electronics applications.