勛圖tv 繚 ENGINEERING GUIDE
PCB Via Current Capacity: Resistance, Loss and Thermal Limits
PCB via current-carrying capacity depends on the plated geometry, connected copper, temperature conditions and acceptable electrical loss. A barrel-resistance calculation can estimate voltage drop and resistive heating for an idealized via. It cannot, by itself, tell you the safe continuous current or predict the temperature rise of a real board.
Begin with the current path
Identify where current enters and leaves the via and how the adjoining planes or traces spread heat. Record continuous current, pulses, duty cycle and the allowed voltage drop. A group of parallel vias may not share current equally if their connections differ in resistance or inductance. Placement and copper access matter as well as the number of holes.
For switching or high-frequency currents, DC resistance is only part of the problem. Transition inductance, return-path geometry and frequency-dependent conductor behavior may require circuit or field analysis. Do not use a DC barrel model as an RF transition model.
Via DC resistance and loss
Via DC resistance and loss
Use the current inputs and keep the assumptions
Start with the example to understand the units and output, then use Clear for my inputs before entering your project. Example mode stays visibly labeled even if you edit its numbers. The form begins without a result so an illustrative value cannot be mistaken for an approved requirement. Every field must have a valid value; zero is accepted only where it has a meaningful role in the particular model.
Read the input notes before calculating. They identify the physical boundary and what is excluded. Keep the same unit convention across the drawing and worksheet. Changing an input invalidates the previous result and disables its download until you calculate again. This prevents an old number from appearing to describe a revised geometry.
The result is a screening record. A negative margin or an out-of-range condition identifies a question to resolve; a positive margin is not a manufacturing approval. Use the record with the actual drawing, material and project requirement. The model does not load CAD files, inspect images or retrieve private factory data.
Download the current result if it helps the discussion. The text includes the entered inputs, result and limitations. It stays on your device until you choose to attach or share it. Contact is a separate step; this page does not automatically populate the enquiry form or upload a file. Avoid confidential identifiers if you only need an exploratory calculation.
| Input | What to establish before using it |
|---|---|
| Review reference | Use a nonconfidential reference that lets you connect this calculation to the correct drawing revision. |
| Finished inside diameter 繚 mm | The model treats the opening as a uniform cylinder. It does not represent a solid copper-filled via or a tapered microvia. |
| Uniform copper wall 繚 micrometers | Use a justified representative wall thickness. Local thinning, defects and interfaces are outside this ideal barrel calculation. |
| Conductive barrel length 繚 mm | Enter the length carrying the modeled current. The full board thickness may not equal the active span for a particular connection. |
| Identical parallel barrels | The calculation assumes equal geometry and equal current sharing. Different plane connections can invalidate that simplification. |
| Total DC current 繚 A | This is an entered operating condition, not a safe-current recommendation. Pulses and AC behavior need separate treatment. |
| Copper resistivity 繚 ohm meter | The example is a near-room-temperature bulk-copper assumption. Temperature rise is not solved; provide suitable properties for your analysis. |
Model the copper that actually carries current
For a uniform cylindrical barrel with finished inside diameter d and copper wall thickness t, copper cross-sectional area is pi times ((d + 2t) squared minus d squared), divided by four. Resistance is resistivity times length divided by that area. The worksheet converts millimeters and micrometers consistently and reports milliohms, millivolts and watts.
The illustrative resistivity represents copper near room temperature. Actual resistance changes with temperature and construction. The tool does not model a thermal feedback loop, contact resistance, necked regions or plating variation. Use a conservative representative geometry for screening, then obtain the appropriate engineering validation.
Example: parallel barrels and unequal sharing
Consider four geometrically identical barrels with equal connections carrying a total DC current. The ideal parallel resistance is one barrel's resistance divided by four. The corresponding total loss is total current squared times the parallel resistance. This result relies on equal current sharing; it is not valid evidence that one poorly connected via cannot become the hottest path.
Changing the count from four to eight halves the ideal resistance if all other assumptions remain equal. It does not necessarily halve board temperature rise because heat spreading, ambient conditions and neighboring power dissipation remain part of the thermal system.
What a current rating needs beyond arithmetic
Define the measurement location and allowed temperature rise, board copper distribution, mounting and airflow, load waveform and relevant production tolerances. Review how the design behaves if plating is thinner at a critical location. Prototype measurements should use a representative layout and environment rather than an isolated test hole with different heat sinking.
Texas Instruments' motor-driver layout guidance provides useful context on copper distribution and via use around power devices. Its examples have their own assumptions. They should not become a universal current-per-via rule for unrelated constructions.
Filled copper and thermal paths
A copper-filled via has a different conductive geometry from a hollow barrel. A resin-filled hole still primarily conducts through the barrel. Conductive paste has material-specific properties and should not be assigned bulk copper resistivity by default. Select the model that represents the actual structure.
Thermal vias also require a heat-flow model with suitable boundary conditions. Electrical resistance and thermal resistance are different quantities, even though both depend on geometry and material. The present tool intentionally reports electrical loss without inventing a junction or board temperature.
Use the result in a design review
Save the entered dimensions, current and assumptions with the output. Compare the predicted voltage drop with the circuit's budget, and use the loss as one input to thermal analysis. If the result changes significantly when plausible plating or current values change, prioritize that uncertainty for verification.
How many vias are enough? The answer depends on electrical and thermal requirements. Can a calculator certify a current rating? This one cannot. What should accompany an enquiry? Supply the stackup, current waveform, copper layout around the transition and the relevant temperature or loss requirement so the discussion can move beyond a hole-count guess.
Connect the local feature to the circuit-level requirement
Start with a requirement expressed at the circuit level: allowable voltage loss, connection topology, return-path continuity or an isolation condition. Then determine which local geometries influence that requirement. A calculation of one copper feature becomes useful when its result is compared with an allocated budget. Without that connection, a precise number can distract from the real system constraint.
Keep DC, transient and high-frequency behavior separate. A resistance calculation can support a DC loss estimate under its stated assumptions. It does not automatically describe inductance, impedance discontinuity or current distribution during a fast transition. Similarly, a geometric clearance can establish separation in a simplified drawing while leaving the electrical safety and field-distribution questions unresolved.
Use the actual material and connection model. Copper thickness, temperature, plane access and interface geometry can alter the result. If several parallel paths are assumed equal, examine whether the layout supports that assumption. A symmetric count on a schematic does not guarantee equal physical paths on the board. Where a model is sensitive to one uncertain input, prioritize that input for measurement or manufacturing confirmation.
Treat tolerances as part of the analysis, not an afterthought. Recalculate with plausible bounds that are supported by the proposed construction. Do not simply add an arbitrary percentage to the final result and call it a safety margin. Identify the source of each bound and whether it represents a nominal variation, a worst-case limit or a statistical estimate. The tools here intentionally do not convert those categories into one another.
Plan prototype verification around the product environment. A bench coupon can be informative, but its copper area, mounting and temperature conditions may differ from the final assembly. Document what the test represents and what it does not. For an isolation or connectivity concern, ensure the chosen inspection can actually observe the relevant condition rather than relying on a visually clean surface.
Keep the result with the drawing revision and the circuit requirement it supports. If the stackup, hole treatment or adjoining copper changes, revisit the calculation instead of assuming the earlier conclusion survives. The appropriate next step may be a manufacturing question, a more detailed simulation or a representative test. The page tool helps identify that step; it is not a release authority or a substitute for a complete electrical design review.
Standards, source context and limits
Use the performance and acceptance documents named in the procurement agreement, including their revisions and any applicable addenda. A design guide explains choices; a product acceptance requirement defines what must be demonstrated. Neither a reference link nor a calculator result is a certification of the board or the supplier. Where a value is contractually important, check the controlled document and agree the measurement method with the responsible parties.
Examples on this page are deliberately labeled and are not advertised 勛圖tv limits. Supplier documentation is linked for the specific material or process context it explains. Equipment photographs and cross-section examples show the subject; they are not current production, inspection or qualification records for your order.