Calculate thermal resistance for up to 6 stacked layers. Includes temperature profile, layer breakdown, heat flux, status indicator, and presets for CPU, LED, and MOSFET thermal paths.
Thermal resistance (R_th) quantifies how much temperature rise occurs per watt of heat dissipated through a material: ΔT = R_th × P. For a slab of thickness t, area A, and thermal conductivity k, the thermal resistance is R_th = t / (kA), measured in °C/W. When multiple layers are stacked in series — as in a chip-to-heatsink assembly — the total thermal resistance is the sum of each layer's contribution.
Proper thermal management is critical in electronics: exceeding a component's maximum junction temperature causes performance degradation, reduced lifetime, or immediate failure. The path from a semiconductor die to ambient air may include a die attach layer, thermal paste, heatsink base, and fins — each contributing to the total thermal resistance.
This calculator lets you model up to 6 stacked thermal layers, each with independent material, thickness, and area. It computes the total thermal resistance, temperature at each interface, heat flux, and a visual temperature profile so you can identify thermal bottlenecks.
Thermal stack-ups involve multiple materials with very different conductivities (copper at 401 W/m·K vs. FR4 at 0.25 W/m·K), so a thin layer of poor conductor can dominate the total thermal resistance. This calculator identifies which layer is the bottleneck and shows the temperature at every interface — information that would require tedious manual calculation for multi-layer assemblies.
Single Layer: R_th = t / (k × A) Series Stack: R_total = R₁ + R₂ + … + Rₙ Temperature Rise: ΔT = R_total × P Junction Temperature: T_j = T_ambient + ΔT Heat Flux: q = P / A (W/m²) Thermal Conductance: G = 1 / R_th (W/°C) Where: t = thickness (m) k = thermal conductivity (W/m·K) A = cross-section area (m²) P = power dissipation (W)
Result: T_j = 49.3 °C
For a CPU dissipating 125 W: the thermal paste layer (0.1 mm, 1600 mm², k=5) has R_th = 0.0001/(5 × 0.0016) = 0.0125 °C/W. The aluminum base (10 mm, 10000 mm², k=237) has R_th = 0.01/(237 × 0.01) = 0.0042 °C/W. Total R_th = 0.0167 °C/W. ΔT = 0.0167 × 125 = 2.09 °C. T_j = 25 + 24.3 = 49.3 °C (well within limits).
Modern processors can dissipate over 300 W in a package smaller than a postage stamp, creating heat flux densities exceeding 100 W/cm². Managing this heat requires careful attention to every layer in the thermal path: die attach, thermal interface material (TIM), heatsink base, and fin array. Each layer contributes thermal resistance, and the total determines whether the chip stays within its safe operating temperature.
TIMs bridge the microscopic air gaps between two mating surfaces. Categories include thermal greases (k = 1-12 W/m·K), phase-change materials (soften at operating temperature for better contact), thermal pads (convenient but higher R_th), and liquid metal (k = 20-70 W/m·K but electrically conductive and corrosive). The choice depends on the application requirements: ease of rework, electrical isolation, and maximum temperature.
For high-performance systems, engineers use copper heat pipes (effective k > 10,000 W/m·K), vapor chambers, thermoelectric coolers (Peltier devices), and direct-die liquid cooling. These technologies reduce effective thermal resistance far below what solid conduction alone can achieve, enabling processors to boost to higher frequencies while staying within thermal limits.
Thermal conductivity (k, in W/m·K) is a material property — how well the material conducts heat. Thermal resistance (R_th, in °C/W) depends on the specific geometry (thickness and area). A highly conductive material in a thin, wide layer has very low thermal resistance.
Without thermal paste, microscopic air gaps between surfaces (roughness ~1-10 μm) trap pockets of still air (k = 0.026 W/m·K). Thermal paste (k = 1-12 W/m·K) fills these gaps, dramatically reducing contact thermal resistance.
This calculator models conduction through solid layers. Add the heatsink-to-air convection resistance (from the heatsink datasheet, typically 0.5-10 °C/W) as an additional equivalent layer. Radiation is usually a small correction at typical electronics temperatures.
This calculator handles different areas for each layer — each layer has its own independent area input. Heat spreading (where heat flows laterally to reach a wider layer) adds a spreading resistance; for accurate modeling, use a spreading resistance formula or FEA.
The 1D series model is accurate when heat flow is primarily in one direction (perpendicular to layers) and layers are wide relative to their thickness. For tall, narrow stacks or when area changes dramatically between layers, 2D/3D heat spreading effects become significant.
Small passive heatsinks: 5-20 °C/W. Medium heatsinks with fan: 0.5-3 °C/W. Large server-class heatsinks: 0.1-0.5 °C/W. Liquid cooling loops: 0.05-0.2 °C/W. The heatsink-to-air resistance is usually the largest term in the total thermal path.