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Designing the dissipation of heat produced by joule effect, 2 practical examples

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Design heat dissipation by joule effect:

The Joule effect is one of the main phenomena that occurs in electronic equipment when electrical energy is converted into thermal energy. In summary, the Joule effect consists of the generation of heat that arises when an electric current flows through a circuit element between two points characterized by a certain potential difference.

The Joule effect, in some cases, is intentional, as in fuses, hair dryers, or electric ovens, but in most cases, it is an unavoidable consequence of the passage of current, which produces unwanted and potentially harmful heat. For those involved in thermal simulation in the design of electronic devices, it represents a problem that must be thoroughly understood within a 3D design environment.

The Joule effect can be effectively analyzed and managed using a tool such as Simcenter FloTHERM XT, the thermal simulation software integrated into PADS Professional, the PCB Design suite developed by Mentor and Siemens for small and medium-sized electronic design companies. In the latest versions of FloTHERM XT, electrical boundary conditions are applied to the periphery of a 3D solid representation of the conductor. The subsequent 3D electro-thermal simulation process calculates the current, potential, and voltage and uses the Joule heating power as a cell-by-cell source for the temperature distribution.

Typical application areas for simulating the heat generated by the Joule effect include busbars, power substrates, and BGA ground planes, as well as leadframes and fuses. These are cases in which heat due to electrical resistance plays a dominant role in total power dissipation.

Example 1 - Thermal simulation of a fuse.
Below we see a simple example of a fuse mounted on a PCB. The fuse cartridge has been omitted for clarity. A current value on the face of the trace leading to the fuse and a fixed voltage value on the edge of the ground plane on the underside of the PCB are defined. A via connects the trail to the return to the ground.

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Below we see a simple example of a fuse mounted on a PCB. The fuse cartridge has been omitted for clarity. A current value on the face of the trace leading to the fuse and a fixed voltage value on the edge of the ground plane on the underside of the PCB are defined. A via connects the trail to the return to the ground.

Flotherm XT
The speed of the arrows is given by the current density, which in turn is closely related to the resulting power dissipation and temperature. Note the high current density inside the winding fuse, achieved by design. FloTHERM XT can also detect the resulting power dissipation due to Joule heating. Since it is a 3D simulation, power density is given in power per volume, in this case / mm3.
Simulazione_3D_Flotherm
The resulting temperature is the most interesting element. The hottest temperatures occurring in the middle section of the fuse were detected here.

The role played by the fuse involves a coupling between the electrical and thermal worlds. An increase in temperature will result in an increase in electrical resistivity, which in turn will increase current density, which will increase Joule heating power, which will increase temperature, and so on. If the heat is removed quickly enough, equilibrium is achieved and conditions stabilize at a constant temperature rise. If the coupling is too strong, especially under high current conditions, the temperature will soar, as long as the fuse does not overheat. FloTHERM XT can handle this coupling through its material property of temperature-dependent electrical resistivity.

Example 2 - PDN analysis of a PCB.
The other example we present shows the effects of Joule heating in the Power Distribution Network (PDN) of a PCB. FloTHERM has a unique technology for representing such complex geometries, defined in 3D within EDA software (in this case PADS Professional), which can be included in a Joule heating simulation. The result is diagrams showing the voltage distribution (more or less uniform, because the PDN works as expected, supplying all the potential difference), the magnitude of the current density, the power dissipation of the resulting Joule heating, and finally the resulting temperature.
In this case, we will have a very small temperature rise on the environment. In "typical" digital electronics, power dissipation in the die of active devices that dominates the thermal behavior of the system, not Joule heating in PDNs.