transient multiphysics simulation of the i-stars module ii/ii-1.pdf · transient multiphysics...
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Transient Multiphysics Simulation of the i-StARS Module
Jean-Louis BLANCHARD – VALEO / GEEDS
Laurent DUPONT – IFFSTAR / LTS
February 1 & 2, 2012
7th European Advanced Technology Workshop on Micropackaging and Thermal Management
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Plan of the presentation
Purpose of the simulation
View of the IFSTTAR experimental setup
Joule effect modelling methods
Description of the simulation model
Geometry
Materials
Mesh
Comparison between simulation and experimental results for two modules
Conclusion
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Purpose of the simulation
Investigate the temperature evolution of an I-StARS module during high intensity transient profiles using two-physics (electrical and thermal) simulation
This power module is a one phase leg switch of a starter generator
Cross-check the simulation results with experimental measurements performed at INRETS (now IFSTTAR)
Investigate the influence of voids in braze layers
Phase connection
Plus connection
Hiside leadframe
Loside leadframeBackplate
Heat sink
Adhesive (leadframes / backplate)
Grease(backplate / heat sink)
dies
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INRETS experimental setup
The experimental setup enables to perform electrical and thermal measurements
The transient time duration requires a high-frequency IR camera
Measurements were made with a MOSFET transistor in avalanche and resistive mode
Simulations are made in resistive mode only
IFFSTAR camera1 kHz frequency acquisition
GEEDS camera
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Joule Effect Modelling
Conventional method: volume heat source model
Estimation of the joule effect power P (W)
Application of a volume heat source Q (Wm-3)
Multiphysics method: electrical thermal model
Specification of the temperature-dependent electrical conductivity or resistivity of materials
Application of electrical boundary conditions (tension / tension) or (tension / intensity)
Computation by the software of the electrical maps and related joule effect
With tension / tension boundary conditions, the multiphysics model enables the automatic adjustment of current with temperature
2RIP VPQ /
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Simulation model geometry
The simulation is based on a concurrent thermal electrical model built with ANSYS Multiphysics
Such a model requires an accurate geometrical representation of the bondings and die stackup of the MOSFET transistor
Die 2
View of the bondings (bonding diameter: 0.5mm)
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Simulation model geometry
View of the die stackup
Intrinsic thermal and electrical properties are used for all materials, with the exception of the silicon die electrical resistivity
The electrical resistivity of the silicon die is modelled in such a way that the resistance across its thickness is equal to the RDSon value of the MOSFET transistor
This equivalent resistivity is temperature-dependent
Leadframe
Lower braze (130µm)
Lower slab (50µm)
Invar (150µm)
Upper slab (50µm)
Upper braze (130µm)
Die (235µm)
Aluminium Layer (10µm)
Bonding
[The adhesive is located between the leadframes and the backplate]
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Simulation model mesh
532 422 nodes
245 811 elements
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Simulation model environmental conditions
Electrical boundary conditions:
0V on the phase connection
100 ms 500A step on the plus connection
Thermal boundary conditions:
23°C prescribed temperature on the radiator back side
Initial temperature: 23°C
Phase connection
Plus connection
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1 2
3 4
Module M3390 simulation Overview
This module has no void in the braze layer
Die #4 is not bonded
Dies #1 and #3 are excluded from the model to reduce the mesh size
Die #2 is the measured one
The simulation predicts that the maximum temperature is reached on the bonding located near the MOSFET gate
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Module M3390 simulation Maps at time 0.1s
Tension mapIn the bondings and die stack
Global temperature map
Temperature mapin the silicon layer
Visualization of the current flow
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Module 3390. Tension difference between connections
0
0,1
0,2
0,3
0,4
0,5
0,6
0,00E+00 1,00E-02 2,00E-02 3,00E-02 4,00E-02 5,00E-02 6,00E-02 7,00E-02 8,00E-02 9,00E-02 1,00E-01
Time (s)
Tens
ion
(V)
Sim.Exp.
Module M3390 simulation Tension comparison
The RDSon value is the maximum one provided by the component manufacturer
9mV
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Module M3390 simulation Temperature map in the aluminium layer
3D view generated with Ansys Parametric Design Language and SCILAB scripts
Die temperature probe
Die temperature probe
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0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
0 10 20 30 40 50 60 70 80 90 100 110
Time (ms)
Nor
mal
ized
tem
pera
ture
Bonding sim.Bonding exp.Die left sim.Die left exp.Die right sim.Die right exp.
Module M3390 simulation Temperature comparison
Avalanche phenomenon during switch off
6°C
19°C
12°C
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Module M3390 simulation Detailed electrical comparison
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Module RX74 simulation
A void with 1.25 mm2 area located in the upper braze layer is inserted in the simulation model
In this figure, the top aluminium and silicon layers are hidden, as well as two bondings
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Module RX74 simulation
Simulated profiles
90
95
100
105
110
115
0 0,002 0,004 0,006 0,008
Curvilinear abscissa (m)
Tem
pera
ture
(°C
)
No voidOne void
Void locationTemperature profiles
Experiment Simulation
Upper curves: with a void
Lower curves: without void
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Conclusion
Main benefits
The inclusion of electrical effects is a key feature for:– Computing the joule effect with a high degree of accuracy– Improving correlatively the reliability of thermal simulations– Cross-checking simulation results with experimental measurements
Multiphysics simulation is the natural way to describe systems where coupled physics phenomena take place
Further work
For the i-StARS module, the next step will consist of modelling the active behaviour of electronic components, to be in a position to process the avalanche mode
More generally, for power modules, the next extension will consist of performing routinely 3-physics simulation dealing with electrical, thermal and CFD (Computational Fluid Dynamics) aspects