Source: https://guthlabs.ai/docs/instruments/heat-sink-thermal-resistance-calculator/

instrument / verified-clean

# Heat Sink Thermal Resistance Calculator

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Inspectable records

[01**Overview**Purpose and lifecycle](<https://guthlabs.ai/docs/instruments/heat-sink-thermal-resistance-calculator/>)[02**Mechanism**Method and assumptions](<https://guthlabs.ai/docs/instruments/heat-sink-thermal-resistance-calculator/mechanism/>)[03**Implementation**Binding and validation](<https://guthlabs.ai/docs/instruments/heat-sink-thermal-resistance-calculator/implementation/>)[04**Qualification**Evidence and errata](<https://guthlabs.ai/docs/instruments/heat-sink-thermal-resistance-calculator/qualification/>)

## Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

**Area**: Electrical & Electronics Engineering — Circuits, Power Systems, Electronics Lab

**Tranche**: tranche-4

**Evidence ID**: t4-290

**Ledger rows**: 1

No ledger note is attached.

## Review findings

The temperature formula is valid as a steady-state estimate. Verdict is NEEDS_REVIEW because the spec claims an output, margin to Tj(max), without defining the required Tj(max) input or the margin formula. The implementation should explicitly add Tj(max), define margin = Tj(max) − Tj, enforce units and numeric constraints, and retain the honest steady-state label.

### Formula and scope findings

- The junction-temperature formula Tj = Ta + P(θJC + θCS + θSA) is standard for a steady-state, single-heat-flow thermal-resistance chain.

- The claimed output 'margin to Tj(max)' has no supplied Tj(max) input and no stated margin formula; the conventional definition is margin = Tj(max) − Tj.

- The formula assumes θJC, θCS, and θSA are valid constant series thermal resistances under the same operating conditions and that all dissipated power flows through this chain.

### Unit assumptions

- P is in watts (W).

- θJC, θCS, and θSA are in °C/W or K/W; these units are numerically equivalent for temperature differences.

- Ta and Tj must use an absolute temperature scale consistently. If Ta is entered in °F, it must be converted to °C or K before adding the thermal rise.

- Tj(max) must use the same temperature scale as Tj when calculating margin.

- The conventional margin formula used in the test vectors is margin = Tj(max) − Tj.

## Boundary hardening

**BREAK_CLAIMED** · SELF_FLAGGED

The specified output includes margin to Tj(max), but the specification provides no Tj(max) input or fixed value, making that output undefined. Additionally, sufficiently large finite JavaScript inputs overflow Tj to Infinity.

## Errata and corrections

No applied erratum is attached to this unique-name record.

## Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

````
{
  "inputs": {
    "Ta": 25,
    "Ta_unit": "°C",
    "P": 10,
    "thetaJC": 1.2,
    "thetaCS": 0.3,
    "thetaSA": 4.5,
    "theta_unit": "°C/W",
    "Tj_max": 125,
    "Tj_max_unit": "°C"
  },
  "expected_outputs": {
    "Tj": 85,
    "Tj_unit": "°C",
    "margin_to_Tj_max": 40,
    "margin_unit": "°C"
  },
  "working": "θtotal = 1.2 + 0.3 + 4.5 = 6.0 °C/W. Temperature rise = 10 W × 6.0 °C/W = 60 °C. Tj = 25 °C + 60 °C = 85 °C. Margin = 125 °C − 85 °C = 40 °C."
}
````

## Related workflows

[Electronics Power-Rail Designerthermal chain](<https://guthlabs.ai/docs/instrument-workflows/power-rail/>)[Heat-Transfer Pathelectronics tie-in](<https://guthlabs.ai/docs/instrument-workflows/heat-path/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json · VERIFIED_CLEAN`

- `evidence-tranche4/tranche4-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`