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AUTOR DO BLOG ENG. ARMANDO CAVERO MIRANDA SAO PAULO BRASIL

sábado, 2 de janeiro de 2010

Thermal Analysis of Semiconductors




Thermal simulation predicts the junction temperature
and life time of semiconductors.

The design of power converter includes necessarily the calculation of power loss and
temperature rise in the semiconductors and heat sink. This article shows the procedure of
evaluation junction temperature and life time of semiconductors.
By Tobias Hofer, Negal Engineering GmbH Switzerland.

The design of power converter includes necessarily the calculation of
power loss and temperature rise in the semiconductors and heat
sink. For a reliable design the temperature ripple of the silicon should
also be considered. The temperature ripple mainly determines the life
time of the semiconductor (number of cycles to failure). The junction
temperature is related to the heat sink temperature. Mostly the heat
sources are not homogenous distributed over the heat sink. Therefore,
the heat distribution on the heat sink must be known.

Case temperature
The lifetime of the power module not only depends on the temperature
difference ΔTj but also on the average junction temperature of
the semiconductor. It makes a difference whether the temperature
swing of 30K is between 60°C and 90°C or between 80°C and
110°C.
It takes a much smaller number of cycles to failure if the
absolute temperature is higher. The junction temperature is relative to
the case temperature of the semiconductor module. The fact that the
heat sources (semiconductors) are not evenly spread over the heat
sink, the heat distribution of the heat sink must be simulated. The
simulation tool used for the simulation in this paper represents the
heat sink as a rectangular plate. One side is cooled by convection.
On the other side rectangular heat sources are placed. The top of the
heat sources and heat sink is isothermal.

For a reliable design of the power converter it is important to calculate
the semiconductors temperature. The significance of simulating
the temperature distribution on the heat sink was shown. Taking the
temperature ripple and the average temperature of the semiconductor
in account leads to safer designs. With adequate simulation software
it is possible to optimize the design during the development
process in an early stage. All simulations in this paper were performed
with SemiSimV1 [3].

References
[1] Realistic benchmarking of IGBT-modules with the help of fast and
easy to use simulation-tool
R.Schnell, U.Schlapbach; ABB Switzerland

[2] Power Cycling Lifetime of Advanced Power Modules for Different
Temperature Swings U.Scheuermann, U.Hecht; SEMIKRON
[3] SemisSimV1, www.negal.ch

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