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Thermal Properties and Testing

Thermal Conductivity Thermal Resistance

The time rate of heat flow through a unit area producing a unittemperature difference across a unit thickness.Thermal conductivity is an inherent or absolute property of the material. The opposition to the flow of heat through a unit area of material across an undefined thickness.Thermal resistance varies with thickness.
INTRODUCTION

Thermal Impedance Test Methods – ASTM D5470

A property of a particular assembly measured by the ratio of thetemperature difference between two surfaces to the steady-state heat flow through them. Factors affecting thermal impedance include: Area: Thickness: Pressure: Time: Increasing the area of thermal contact decreasesthermal impedance. Thermal impedance decreases over time. Increasing mounting pressure under ideal conditionsdecreases thermal impedance. Increasing the insulator thickness increasesthermal impedance. Measurement: Thermal impedance is affected by the method oftemperature measurement. Thermal Impedance Per Bergquist TO-220 ThermalPerformance (25
2 in. diameter stack (ref. 3.14 in 2 ) – 10-500 psi, 1 hour per layer o C Cold Plate Testing)
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