Documentation sections

Microvia Current Capacity Calculator

POSThttps://rftools.io/api/py/v1/calculate

Slug microvia-current-capacity. Calculate laser-drilled microvia current capacity from barrel cross-section using IPC-2221, with DC resistance, voltage drop, current density, self-heating, and IPC-2226 aspect-ratio checks.

Inputs

Send every one of these in inputs, in the units shown. Most are required: a call without one is refused (400) and costs nothing; one the calculator can do without takes the default shown. An input outside its range is still computed and flagged in the provenance.

Inputs of microvia-current-capacity
Name	Unit	Range	Default	Description
viaDiameternumber	mm	0.05 … 0.25	0.1	Laser-drilled capture diameter. IPC-2226 defines a microvia as ≤ 0.15 mm.
platingThicknessnumber	µm	5 … 40	18	IPC-6012 microvia barrel plating (blind and buried microvias), Classes 2 and 3: 12 µm average, 10 µm minimum at the thinnest point. Through-holes need 20 µm average (Class 2) or 25 µm (Class 3).
viaDepthnumber	mm	0.02 … 0.25	0.075	Dielectric thickness between the capture and target layers.
tempRisenumber	°C	1 … 100	10	Allowed Temperature Rise
currentnumber	A	0.001 … 20	0.25	Current through the whole array, split evenly between the parallel vias.
numViasnumber	none	1 … 200	1	Parallel Microvias
temperaturenumber	°C	−40 … 150	25	Sets copper resistivity; does not change the IPC-2221 capacity, which is a rise above ambient.
conductorClassnumber	none	0 … 1	0	The IPC-2221A curve the barrels are read on: internal (conservative; the vias are buried) or external (the pads sink heat). IPC-2152 uses its conservative chart either way.One of: 0 Internal (k = 0.024) · 1 External (k = 0.048)
standardnumber	none	0 … 1	0	The rule the design current is checked against, both read at the vias’ summed barrel cross-sectionOne of: 0 IPC-2221A Fig. 6-4 · 1 IPC-2152 §A.3.4

Outputs

Returned in values, by key. A value that is unbounded or undefined is null.

Outputs of microvia-current-capacity
Field	Unit	Description
currentIpcInternalAheadline	A	Capacity per Via (internal, conservative)
currentIpcExternalA	A	Capacity per Via (external k)
arrayCapacityA	A	IPC-2221 Figure 6-4, note 5: closely spaced parallel vias are rated by their summed cross-section, so N vias carry N^0.725 times one via
barrelAreaMm2	mm²	Barrel Cross-Section
resistanceMOhm	mΩ	Resistance per Via
resistanceArrayMOhm	mΩ	Array Resistance
voltageDropMV	mV	Voltage Drop
powerDissipationMW	mW	Power Dissipation
deltaTSelfHeat	°C	Peak rise of a barrel heated along its length with both ends at the pad temperature: P·L/(8·k·A·N)
currentDensityAPerMm2	A/mm²	Current Density
aspectRatio	:1	Aspect Ratio (depth : diameter)
limitCurrent	A	The most current the vias may carry at the allowed rise, read on the chosen chart at their summed barrel cross-section
limitPercent	%	The design current as a percentage of the limit; above 100 % does not comply
minVias	none	The fewest parallel microvias whose summed cross-section carries the design current within the limit
minViaDiameter	mm	The microvia diameter at which the design current equals the limit with this count and plating; at or above it the vias comply

Calling it

Calculate: one call, the request and response in full, and its errors.
Batch: this calculator with others, or a sweep, in one request.
Solve for a target: the value of one input that brings an output to a target.

curl -X POST https://rftools.io/api/py/v1/calculate \
  -H "X-API-Key: $RFTOOLS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "slug": "microvia-current-capacity",
    "inputs": {
      "viaDiameter": 0.1,
      "platingThickness": 18,
      "viaDepth": 0.075,
      "tempRise": 10,
      "current": 0.25,
      "numVias": 1,
      "temperature": 25,
      "conductorClass": 0,
      "standard": 0
    }
  }'

import rftools

client = rftools.Client()  # reads RFTOOLS_API_KEY, or the key `rftools login` saved

result = client.calculate("microvia-current-capacity", {
    "viaDiameter": 0.1,
    "platingThickness": 18,
    "viaDepth": 0.075,
    "tempRise": 10,
    "current": 0.25,
    "numVias": 1,
    "temperature": 25,
    "conductorClass": 0,
    "standard": 0,
})
print(result.values)
print(result.warnings, result.provenance.formula_ref)

const response = await fetch("https://rftools.io/api/py/v1/calculate", {
  method: "POST",
  headers: {
    "X-API-Key": process.env.RFTOOLS_API_KEY,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "slug": "microvia-current-capacity",
    "inputs": {
      "viaDiameter": 0.1,
      "platingThickness": 18,
      "viaDepth": 0.075,
      "tempRise": 10,
      "current": 0.25,
      "numVias": 1,
      "temperature": 25,
      "conductorClass": 0,
      "standard": 0
    }
  }),
});
console.log(response.status, await response.json());

package main

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
	"os"
)

func main() {
	body := []byte(`{
	  "slug": "microvia-current-capacity",
	  "inputs": {
	    "viaDiameter": 0.1,
	    "platingThickness": 18,
	    "viaDepth": 0.075,
	    "tempRise": 10,
	    "current": 0.25,
	    "numVias": 1,
	    "temperature": 25,
	    "conductorClass": 0,
	    "standard": 0
	  }
	}`)
	req, err := http.NewRequest("POST", "https://rftools.io/api/py/v1/calculate", bytes.NewReader(body))
	if err != nil {
		panic(err)
	}
	req.Header.Set("X-API-Key", os.Getenv("RFTOOLS_API_KEY"))
	req.Header.Set("Content-Type", "application/json")
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()
	out, _ := io.ReadAll(res.Body)
	fmt.Println(res.Status, string(out))
}

application/json

{
  "slug": "microvia-current-capacity",
  "values": {
    "currentIpcInternalA": 0.2761999651813298,
    "currentIpcExternalA": 0.5523999303626596,
    "arrayCapacityA": 0.2761999651813298,
    "barrelAreaMm2": 0.004636990756698534,
    "resistanceMOhm": 0.28434668090070625,
    "resistanceArrayMOhm": 0.28434668090070625,
    "voltageDropMV": 0.07108667022517656,
    "powerDissipationMW": 0.01777166755629414,
    "deltaTSelfHeat": 0.0000933259667197919,
    "currentDensityAPerMm2": 53.9142761151407,
    "aspectRatio": 0.7499999999999999,
    "limitCurrent": 0.2761999651813298,
    "limitPercent": 90.51413161325742,
    "minVias": 1,
    "minViaDiameter": 0.08946811379099469
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:microvia-current-capacity",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "IPC-2221A (2003) Figure 6-4 (conductor current capacity, the chart of IPC-2221, 1998), through its published fit; IPC-2226 (HDI design, microvia definition and aspect ratio); IPC-6012 (plating thickness classes); IPC-TM-650 2.6.27 (microvia thermal shock)",
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "viaDiameter": {
          "min": 0.05,
          "max": 0.25,
          "unit": "mm"
        },
        "platingThickness": {
          "min": 5,
          "max": 40,
          "unit": "µm"
        },
        "viaDepth": {
          "min": 0.02,
          "max": 0.25,
          "unit": "mm"
        },
        "tempRise": {
          "min": 1,
          "max": 100,
          "unit": "°C"
        },
        "current": {
          "min": 0.001,
          "max": 20,
          "unit": "A"
        },
        "numVias": {
          "min": 1,
          "max": 200,
          "unit": ""
        },
        "temperature": {
          "min": -40,
          "max": 150,
          "unit": "°C"
        },
        "conductorClass": {
          "min": 0,
          "max": 1,
          "unit": ""
        },
        "standard": {
          "min": 0,
          "max": 1,
          "unit": ""
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "viaDiameter": 0.1,
      "platingThickness": 18,
      "viaDepth": 0.075,
      "tempRise": 10,
      "current": 0.25,
      "numVias": 1,
      "temperature": 25,
      "conductorClass": 0,
      "standard": 0
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "viaDiameter"
      ],
      "msg": "Input should be a valid number, unable to parse string as a number",
      "input": "abc"
    }
  ]
}

An input sent as text. Nothing was counted.

{
  "detail": "More than 120 requests in 60 seconds from this address.",
  "errorKind": "rate_limited",
  "limit": 120,
  "windowSeconds": 60,
  "upgradeUrl": "https://rftools.io/pricing/"
}

Too many requests in a minute, with Retry-After.

Same inputs on the calculator pageMicrovia Current Capacity Calculator, at these values