Safe Current and Power Density Limits in PCB Copper(in A/m² and W/m³) simulation - Page 1
Forum section: electronics / projects

author: electronx
author_rank: Regular Contributor
timestamp: July 07, 2025, 08:35:19 pm
content: Hi everyone,I'm running power and thermal simulations on a custom power PCB design, and I’m trying to determine safe design margins for both current density (A/m²) and power density (W/m³) in copper traces.While there are many discussions and references for current density (e.g. IPC-2152), I’m struggling to find concrete numerical thresholds for both parameters — especially power density — in real-world, simulation-driven design flows.In my simulations, I observe the following:Current density in the range of 3–10 × 10⁶ A/m² depending on the traceLocalized power density hotspots reaching 1 × 10⁸ W/m³ or higherI’m wondering whether those are acceptable or pose a thermal reliability risk.My Key Questions:Do you have or follow any safe-limit chart or table (e.g. rule-of-thumb thresholds) for:Current density (A/m²)Outer layers, continuous power tracesOuter layers, short transient pulsesInner layers continuous power tracesInner layers, short transient pulses******************************************************Power density (W/m³)Current density (A/m²)Outer layers, continuous power tracesOuter layers, short transient pulsesInner layers continuous power tracesInner layers, short transient pulses---------------------------------------------------I want to set a reference table for myselfHave you correlated simulation results (thermal/power maps) with measured failures or temperature data in your designs?Do tools like solvers align well with lab observations in terms of these limits?A structured reference (chart/table) would be incredibly helpful — something I can use to say “we are safe here” when looking at simulation results.Thanks in advance for your experience and any data or papers you can share!

author: thm_w
author_rank: Super Contributor
timestamp: July 08, 2025, 12:39:32 am
content: Isn't this going to depend on airflow (or none if passive) and ambient temperature spec?https://resources.altium.com/p/copper-current-density-simulations-quick-and-dirty-way

author: electronx
author_rank: Regular Contributor
timestamp: July 08, 2025, 08:40:08 am
content: there is no any cooler

author: mtwieg
author_rank: Frequent Contributor
timestamp: July 08, 2025, 04:03:42 pm
content: I'm not aware of any standard beyond IPC-2152, which is still very crude and tends to overestimate temperature rise.It's a fundamentally challenging problem with no general solution. Heat transfer from the board to ambient is perhaps the biggest confounding factor. It's actually harder to estimate under natural convection conditions, due to its inherent nonlinearity and dependence on orientation and spacings.I don't think there's any way to make "rules of thumb" about current density limits without ending up overly conservative in some cases or underestimating temperature in others. Temperature rise is the bottom line (and perhaps temperature gradient as well), not current or power.

author: electronx
author_rank: Regular Contributor
timestamp: July 08, 2025, 05:18:12 pm
content: Hello, I’ve obtained some average reference values from a Chinese company. Now, if we assume that the copper is cooled using nitrogen gas, then practically speaking —disregarding factors such as:Lorentz forcesElectromigrationDielectric breakdown / arcingAnd even in non-superconducting systems— we can theoretically pass any amount of current through the conductor.But we are not using coolingIn this case, for a PCB without any active cooling,the only critical factor becomes the peak temperature the conductor can reach while carrying such high current levels under passive cooling at 25 °C (i.e., without any heatsinks or airflow).If the temperature reaches a point of thermal saturation and stabilizes at desired levels such as 10–15–20 °C, and remains steady in saturation,then it can be considered safe to conduct such current continuously.Therefore, after observing the reference values, the best option would be to run a thermal simulation in a convection-limited enclosure

author: mtwieg
author_rank: Frequent Contributor
timestamp: July 08, 2025, 10:29:23 pm
content: Quote from: electronx on July 08, 2025, 05:18:12 pmUh not sure what nitrogen atmosphere has to do with anything.QuoteOk....QuoteRight, if you have the equipment to do so, then this is the best option.