// MechanicalAI Engineering — Thermal Analysis Tools

Junction-to-Ambient
Thermal Resistance Calculator

Full Rja stack: Rjc + Rcs (TIM) + Rsa (heatsink) · Junction temperature · Thermal margin

Component Parameters

Power Dissipation P

Watts (W) — from datasheet or power budget

Rjc — Junction to Case R_jc

°C/W — from component datasheet (θjc)

Max Junction Temp T_jmax

°C — from datasheet (typically 125°C or 150°C)

Environment Parameters

Ambient Temperature T_amb

°C — worst-case operating ambient

Heatsink Rsa R_sa

°C/W — heatsink thermal resistance (0 if no heatsink)

Rjb (optional) R_jb

°C/W — junction-to-board (for PCB conduction path)

TIM — Thermal Interface Material (Rcs)

Select your TIM or enter a custom Rcs value. Rcs = t / (k × A) where t = bond line thickness, k = conductivity, A = contact area.

Or enter custom R_cs 0.00 °C/W

°C/W — custom TIM resistance (overrides selection above)

Contact Area A

mm² — component footprint / heatsink contact area

Bond Line Thickness t

mm — compressed thickness of TIM

Enter inputs above and click Calculate →

◈ AI Thermal Engineering Assessment

Calculate first, then get an AI-powered thermal analysis with design recommendations.

TIM Thermal Conductivity Reference

TIM Type	Conductivity k (W/m·K)	Typical BLT	Rcs @ 100mm², 0.1mm	Best For
Thermal Grease (standard)	3–6	0.05–0.15mm	0.17–0.33 °C/W	Heatsinks, processors
Phase Change Material	3–8	0.05–0.1mm	0.13–0.33 °C/W	High performance, reflow
Thermal Pad (soft)	3–10	0.5–2.0mm	0.50–3.33 °C/W	Gap filling, PCB boards
Indium Foil	81	0.05–0.25mm	0.006–0.03 °C/W	High power, space-grade
Graphite Sheet	5–10 (z-axis)	0.1–0.5mm	0.10–1.00 °C/W	Spreading, flex apps
Epoxy (thermally conductive)	1–3	0.05–0.2mm	0.17–2.00 °C/W	Permanent bond, structural
Dry / No TIM	~0.03 (air)	N/A	33+ °C/W	Low power only

Typical Component Tjmax Values

Component Type	Typical Tjmax	Notes
General purpose ICs	125°C	Most commercial semiconductors
High-reliability / MIL-spec ICs	150°C	Automotive, defense grade
Power MOSFETs / IGBTs	150–175°C	Check per-device datasheet
LEDs (high power)	125–150°C	Lumen maintenance affects lower limit
Electrolytic capacitors	85–105°C	Lifetime-limiting component
Avionics / space grade	125°C	Typically derated to 110°C max