Online proceedings - EDA Publishing Association

11-13
May 2011, Aix-en-Provence, France
Accurate Thermal Characterization of Power
Semiconductor Packages by Thermal Simulation and
Measurements
Andras Vass-Varnai (1,2) , Robin Bornoff (2) , Sandor Ress (1,2) , Zoltan Sarkany (2) , Sandor Hodossy (1) , Marta Rencz (1,2)
Budapest University of Technology and Economics (1)
Mentor Graphics Mechanical Analysis Division (2)
@eet.bme.hu
@mentor.com
In this paper the possibility of generating a compact thermal
model based on thermal transient measurements is discussed and
evaluated. A case study of a power diode in a cylindrical-shaped
copper package is shown. The detailed model of the package is
built and simulated in a CFD based thermal simulator software.
The measurement results are compared to the results of the
simulations and after some model refinement we found good
agreement. The compact model of the package is also identified
based on the structure functions generated from the real
measurement. The case-node is determined using the standard
dual-interface method. The resulting compact model has proven
to be a perfect representation of the real package as the structure
functions generated based on measurements and corresponding
simulation results match perfectly.
I. INTRODUCTION
As the functionality of thermal simulators gets more and
more complex, measurement techniques also improve.
Thermal engineers face an increasingly difficult task to
make the right selection from the existing tools. Beside this
problem the precise determination of thermal performance
indicators such as RthJC or RthJB is becoming more and
more difficult as the package geometries become more
complex. The thermal characterization of novel power
packages hosting a number of dies is a major issue where
the standard definitions cannot be applied anymore [1,2].
The answer to these challenges may lie in a combined
measurement and simulation approach. Measurements yield
a structure description of materials having different
conductivities; simulation gives the clue as to what certain
sections in the measured structure correspond to. TIM
materials are very difficult to model, as neither their
conductivity nor their thickness can be determined with
high accuracy even by the designer of a given package.
Well planned thermal measurements are suitable tools to
measure the in-situ resistance of these materials so that they
can be later on used for accurate model creation. Another
example may be the junction-to-case thermal resistance
measurement of power packages where the single R thJC
value obtained by measurements may not be a perfect
indicator due to the complex heat-spreading path. In such
cases steady-state simulations may show the temperature
variation on the case surface which is a good basis to verify
whether the simple R thJC approach is valid for the given
package or not.
As the measurement and simulation techniques mutually
support each-other, the ultimate solution for package
thermal characterization may be the simulation model
creation based on real measurements [3].
II. Experimental
In order to compare simulation results with actual
measurements a power diode package was selected having a
cylindrical package shape and a hexagonal silicon diode
inside.
Fig. 1: Package structure of the studied diode (actual on left, 3D model on
right)
The package is app. 8.4 mm high and has a 12.5 mm
diameter cooling surface on its bottom. The hexagonal die is
located in the top region of the package and it is mounted
using a top and bottom die attach layer to the copper
cylinders. The edges of the hexagon are located on a 8.1
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