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

instrument mechanism / verified-clean

# Heat Sink Thermal Resistance Calculator mechanism

The inspectable method record for Heat Sink Thermal Resistance Calculator, kept separate from implementation and qualification.

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

## Model scope

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.

- 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.

## Units and conventions

- 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.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "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."
}
````

## Failure boundary

**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.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/heat-sink-thermal-resistance-calculator/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/heat-sink-thermal-resistance-calculator/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/heat-sink-thermal-resistance-calculator/qualification/>)

## Sources and evidence

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

- `VERIFIED_LEDGER.json`

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

- `BOUNDARY_HAZARD_CATALOG.json`