Documentation sections

Thermal Via Array Calculator

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

Slug thermal-via-array. Calculate thermal resistance of a PCB thermal via array for heat spreading from SMD packages to inner copper planes or heatsinks.

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 thermal-via-array
Name	Unit	Range	Default	Description
numViasnumber	vias	1 … 10000	9	Total number of thermal vias in the array
viaDiameternumber	mm	0.05 … 5	0.3	Via drill hole diameter. IPC-7093 recommends 0.2–0.4mm for thermal vias.
platingThicknessnumber	μm	1 … 200	25	Via barrel copper plating thickness. Typical PCB: 18–35μm. The barrel is always copper; any fill occupies the bore inside it.
pcbThicknessnumber	mm	0.1 … 10	1.6	PCB thickness (length of the via thermal path)
copperThermalnumber	W/m·K	at least 1	385	Thermal conductivity of the via fill material. Copper: 385, silver: 430, thermal epoxy: 1–5. The plated barrel is copper (385 W/m·K) whatever the fill.
drillFillnumber	none	0 … 1	0	Fraction of the bore inside the plating that is filled, from 0 (a hollow plated via) to 1 (fully filled with the material above, copper by default). Copper-filled vias offer the best thermal performance.

Outputs

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

Outputs of thermal-via-array
Field	Unit	Description
thetaPerVia	°C/W	Thermal resistance of a single via
thetaArrayheadline	°C/W	Total thermal resistance of all vias in parallel: θ_array = θ_via / N
effectiveConductance	W/°C	Thermal conductance of the array (reciprocal of θ_array)

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": "thermal-via-array",
    "inputs": {
      "numVias": 9,
      "viaDiameter": 0.3,
      "platingThickness": 25,
      "pcbThickness": 1.6,
      "copperThermal": 385,
      "drillFill": 0
    }
  }'

import rftools

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

result = client.calculate("thermal-via-array", {
    "numVias": 9,
    "viaDiameter": 0.3,
    "platingThickness": 25,
    "pcbThickness": 1.6,
    "copperThermal": 385,
    "drillFill": 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": "thermal-via-array",
    "inputs": {
      "numVias": 9,
      "viaDiameter": 0.3,
      "platingThickness": 25,
      "pcbThickness": 1.6,
      "copperThermal": 385,
      "drillFill": 0
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "thermal-via-array",
	  "inputs": {
	    "numVias": 9,
	    "viaDiameter": 0.3,
	    "platingThickness": 25,
	    "pcbThickness": 1.6,
	    "copperThermal": 385,
	    "drillFill": 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": "thermal-via-array",
  "values": {
    "thetaPerVia": 192.41400439917464,
    "thetaArray": 21.379333822130516,
    "effectiveConductance": 0.046774142184208944
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:thermal-via-array",
    "version": "api@3f2c1a9b04de",
    "formulaRef": null,
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "numVias": {
          "min": 1,
          "max": 10000,
          "unit": "vias"
        },
        "viaDiameter": {
          "min": 0.05,
          "max": 5,
          "unit": "mm"
        },
        "platingThickness": {
          "min": 1,
          "max": 200,
          "unit": "μm"
        },
        "pcbThickness": {
          "min": 0.1,
          "max": 10,
          "unit": "mm"
        },
        "copperThermal": {
          "min": 1,
          "max": null,
          "unit": "W/m·K"
        },
        "drillFill": {
          "min": 0,
          "max": 1,
          "unit": ""
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "numVias": 9,
      "viaDiameter": 0.3,
      "platingThickness": 25,
      "pcbThickness": 1.6,
      "copperThermal": 385,
      "drillFill": 0
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "numVias"
      ],
      "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 pageThermal Via Array Calculator, at these values