Heat Sink

Deterministic engineering intelligence platform for mechanical, structural, and electrical designers. 91 modules validated solvers, 3D CAD workspace, and ISO/DIN standards compliance.

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▸Formula · assumptions · example(JEDEC JESD51 (Thermal measurement) · MIL-HDBK-251 · IEEE Thermal Standards)

Formula

R_{\theta,sa} = \frac{T_j - T_a}{P} - R_{\theta,jc} - R_{\theta,cs}, \quad R_{\theta,\text{conv}} = \frac{1}{h \cdot A_{\text{fin}}}

Junction-to-ambient thermal resistance network, forced/natural convection heat transfer coefficient h, and fin efficiency ηf.

Assumptions

  • · 1D steady-state thermal resistance network through TIM (Thermal Interface Material) interface
  • · Uniform heat flux distribution across heat sink base plate
  • · Convective heat transfer coefficient h calibrated for natural convection (5-25 W/m²K) or forced air (20-100 W/m²K)

Worked example

Worked example — Power Inverter Transistor (P = 45 W, Tj,max = 125 °C, Ta = 40 °C, Rjc = 0.5 K/W, Rcs = 0.3 K/W)

Maximum allowable sink-to-ambient thermal resistance Rsa = (125-40)/45 - 0.8 = 1.09 K/W, sizing an extruded aluminum fin pack with A = 0.085 m².