Thermal territory

	Thermal Territory for a Component
Online calculator for the thermal territory needed to cool a component mounted on a PCB. A more elaborate procedure is implemented in the Btemp program. Install the demo version and select "Estiamte" - "Thermal territories" to get an idea how smooth this procedure works on a real world problem. Related links Learn about thermal design for electronics Online unit conversion More online tools Comments Your need to install a Java console to display this applet. All modern browsers have this option. General The concept is explained in the articles The Thermal Territory Concept, part 1 and The Thermal Territory Concept, part 2. A thermal territory is defined as the smallest area of a PCB that a component needs for its cooling. The size of that area depends on a hand full of parameters such as the size of the component, the heat dissipated, the thermal conductivity in the PCB and the allowed temperature difference. A thermal territory is also associated with a thermal efficiency which is defined as the ratio of the actual heat dissipated and the fictive heat dissipation if the territory had been isothermal. The thermal characteristics of the component are also important. This implementation uses a simple 2-resistor model. The calculated component temperatures and heat flows can be can be viewed by clicking on the component radio button. Chapter 11 of the theory document explains the concept more in detail. Inputs Therm cond Is the thermal conductivity of the PCB. See Thermal conductivity for PCBs. Thickness Is the thickness of the PCB. Heat tr coeff Is the local heat transfer coefficient. It is a parameter that depends on the air velocity and various PCB parameters. The log mean value at Heat transfer coefficient for parallel plates can be used as a first approach. Board temp Is the average temperature of the PCB below the component. A worst case standard approach is 75 C for commercial grade and 90 C for industrial grade components. Air temp Is the air temperature above the component. Width Is the width of the component. Height Is the height of the component. Rjb Is the thermal resistance from the chip to the heat carrying layers of the PCB. Rjc Is the thermal resistance from the chip to the top of the component. Rca Is the thermal resistance from the top of the component to the air. This resistance is determined by the heat transfer coefficient, the top factor and the size of the component. Top factor Is a multiplier for the heat transfer coefficient on the top of the component. 1.0 signifies the same value as for the PCB. 2.0 is a reasonable approximation for forced convection in the range 1 - 2 m/s. This factor can also be used to simulate a heat sink: Monitor the component window and adjust the factor until the Rca resistance corresponds to the conditions wanted. Top of page

Thermal Territory for a Component

Online calculator for the thermal territory needed to cool a component mounted on a PCB.

A more elaborate procedure is implemented in the Btemp program. Install the demo version and select "Estiamte" - "Thermal territories" to get an idea how smooth this procedure works on a real world problem.

Related links
Learn about thermal design for electronics
Online unit conversion
More online tools
Comments

General

The concept is explained in the articles The Thermal Territory Concept, part 1 and The Thermal Territory Concept, part 2.

A thermal territory is defined as the smallest area of a PCB that a component needs for its cooling. The size of that area depends on a hand full of parameters such as the size of the component, the heat dissipated, the thermal conductivity in the PCB and the allowed temperature difference.

A thermal territory is also associated with a thermal efficiency which is defined as the ratio of the actual heat dissipated and the fictive heat dissipation if the territory had been isothermal.

The thermal characteristics of the component are also important. This implementation uses a simple 2-resistor model. The calculated component temperatures and heat flows can be can be viewed by clicking on the component radio button.

Chapter 11 of the theory document explains the concept more in detail.

Inputs

Therm cond
Is the thermal conductivity of the PCB. See Thermal conductivity for PCBs.

Thickness
Is the thickness of the PCB.

Heat tr coeff
Is the local heat transfer coefficient. It is a parameter that depends on the air velocity and various PCB parameters. The log mean value at Heat transfer coefficient for parallel plates can be used as a first approach.

Board temp
Is the average temperature of the PCB below the component. A worst case standard approach is 75 C for commercial grade and 90 C for industrial grade components.

Air temp
Is the air temperature above the component.

Width
Is the width of the component.

Height
Is the height of the component.

Rjb
Is the thermal resistance from the chip to the heat carrying layers of the PCB.

Rjc
Is the thermal resistance from the chip to the top of the component.

Rca
Is the thermal resistance from the top of the component to the air. This resistance is determined by the heat transfer coefficient, the top factor and the size of the component.

Top factor
Is a multiplier for the heat transfer coefficient on the top of the component. 1.0 signifies the same value as for the PCB. 2.0 is a reasonable approximation for forced convection in the range 1 - 2 m/s. This factor can also be used to simulate a heat sink: Monitor the component window and adjust the factor until the Rca resistance corresponds to the conditions wanted.

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