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ThématiquesEPASF - FARMAN calculsFIABILITE DESCOMPOSANTS DEPUISSANCESylvain PIETRANICO (SATIE/LMT)Sylvie POMMIER (LMT)Stéphane LEFEBVRE (SATIE)

Fracture mechanism – (a)When extreme loads are applied, abrittle fracture of the ceramic isobservedThe crack path is normal to themaximum principal stress in theceramic layer .type (a) – failureBrittle fracture of the ceramicEssai de tractioncompression

Fracture mechanism – (b)Tiny crack near the copper/ceramicinterface – type (b) failure.Fatigue crack growth in copperalong the copper/ceramic interfaceEssai de tractioncompressionThe fatigue life of the componentis equal to the number of striationscounted on the fracture surface.This damage mechanisms is theone limiting the fatigue life.

ApproachCopperCeramic (NiAl or Si 3 N 4 )SingularitiesFE modelCopper – elastic plasticCeramic - elasticNon singular area : WEIBULL STRESS DISTRIBUTION-A crack initiation criteria-Stochastic : the fracture stress is statistically distributedbecause initiation sites statistically are statistically distributed (pores, grain boudary, second phases)-Scale effectsSingular area : FRACTURE MECHANICS FRAMEWORK-A crack growth criteria-Deterministic : no need to create a singularity, it pre-exists-Criteria : at which condition this singularity can move

Characterization of the materials : ceramics- brittle- failure stress statistically distributed- scale effect•Bending tests•2 ceramics- NiAl Aluminium nitride-Si 3 N 4 Silicon nitride•3 geometriesthin : t=0.5 mm , w=2.5large : t=0.5 mm , w=10 mmthick : t=1 mm , w=2.5 mmNiAl

Characterization of the materials : ceramicsPF( dV ) = 1 − P ( dV )S=Weibull distributionm⎛⎞⎜ dV ⎛ σ ⎞1 − exp − ⎟⎜⎜⎟V ⎟⎝o ⎝ σ 0 ⎠ ⎠Three points bendingtest

Characterization of the materials : ceramicsPF( dV ) = 1 − P ( dV )S=Weibull distributionm⎛⎞⎜ dV ⎛ σ ⎞1 − exp − ⎟⎜⎜⎟V ⎟⎝o ⎝ σ 0 ⎠ ⎠Three points bendingtestStress field in 3 points bendingσ22 yt⎛( x, y) = ⎜1− ⎟ σ max⎝xL⎞⎠

Characterization of the materials : ceramicsPF( dV ) = 1 − P ( dV )S=Weibull distributionm⎛⎞⎜ dV ⎛ σ ⎞1 − exp − ⎟⎜⎜⎟V ⎟⎝o ⎝ σ 0 ⎠ ⎠Three points bendingtestStress field in 3 points bendingσ22 yt⎛( x, y) = ⎜1− ⎟ σ max⎝xL⎞⎠PF( ) ( )V= 1 − P = − ∫S V 1 expV−dVVo⎛ σ⎜⎝ σ 0( x,y)⎞⎟⎠mWeakest link theorym⎛ ⎞⎜ ⎛ σW⎞= 1 − exp − ⎟⎜⎜⎟⎟⎝ ⎝ σ 0 ⎠ ⎠

Characterization of the materials : ceramicsPF( dV ) = 1 − P ( dV )S=Weibull distributionm⎛⎞⎜ dV ⎛ σ ⎞1 − exp − ⎟⎜⎜⎟V ⎟⎝o ⎝ σ 0 ⎠ ⎠Three points bendingtestStress field in 3 points bendingσ22 yt⎛( x, y) = ⎜1− ⎟ σ max⎝xL⎞⎠PF( ) ( )V= 1 − P = − ∫S V 1 expV−dVVo⎛ σ⎜⎝ σ 0( x,y)⎞⎟⎠mWeakest link theorym⎛ ⎞⎜ ⎛ σW⎞= 1 − exp − ⎟⎜⎜⎟⎟⎝ ⎝ σ 0 ⎠ ⎠Where, in 3 points bendingσW= σmax⎛⎜⎝V 1eff ⎞Vo⎟ ⎟ ⎠mandVeff⎛ σ x,= ∫ ⎜V ⎝ σ( )y⎞⎟⎠mdV=⎛V⎜2⎞⎟max ⎝ ⎠ 11( ) 2+m

Characterization of the materials : ceramicsP F= 1 −⎛exp⎜−⎜⎝⎛ σW⎜⎝ σ 0⎞⎟⎠m⎞⎟⎟⎠σW= σmax⎛⎜⎝V 1eff ⎞Vo⎟ ⎟ ⎠m⎛ L.t.w ⎞ 1V eff = ⎜ ⎟⎝ 2 ⎠ 1 + m( ) 2Aluminium NitrideAlNmσ= 9.56o = 360MPaSilicon NitrideSi 3 N 472m = 13.σ =o 470MPa

Characterization of the materials : ceramics- brittle- failure stress statistically distributed- scale effect•Bending tests•2 ceramics- NiAl Aluminium nitride-Si 3 N 4 Silicon nitride•3 geometriesthin : t=0.5 mm , w=2.5large : t=0.5 mm , w=10 mmthick : t=1 mm , w=2.5 mmNiAl

Range of applicabilityPF( )( )FEdV σ x,y,zV = 1 − exp ∫ − ⎜VFEVFEo⎛⎜⎝FEσ0⎟ ⎞⎠mWhereσFE( x,y,z )is the positive part of the maximum principal stress in the sub volume dVAluminium NitrideAlNmσ= 9.56o = 360MPaSilicon NitrideSi 3 N 4m = 13. 72σ =o 470MPaThe smallest AlN effective volume is equal to 0.07 mm 3The smallest Si 3 N 4 effective volume is equal to 0.03 mm 3 .( )1 dσxThe maximum value of is equal to 4mm -1 .σ ( x ) d x

ApproachCopperCeramic (NiAl or Si 3 N 4 )SingularitiesFE modelCopper – elastic plasticCeramic - elasticNon singular area : WEIBULL STRESS DISTRIBUTION-A crack initiation criteria-Stochastic : the fracture stress is statistically distributedbecause initiation sites statistically are statistically distributed (pores, grain boudary, second phases)-Scale effectsSingular area : FRACTURE MECHANICS FRAMEWORK-A crack growth criteria-Deterministic : no need to create a singularity, it pre-exists-Criteria : at which condition this singularity can move

Finite element simulationsCopperCeramic (NiAl or Si 3N 4)SingularitiesFor the Weibull analysis, thesingular area are excluded : ( )σ xd( x ) 11 σ−d x≥4mm

ApproachCopperCeramic (NiAl or Si 3 N 4 )SingularitiesFE modelCopper – elastic plasticCeramic - elasticNon singular area : WEIBULL STRESS DISTRIBUTION-A crack initiation criteria-Stochastic : the fracture stress is statistically distributedbecause initiation sites statistically are statistically distributed (pores, grain boudary, second phases)-Scale effectsSingular area : FRACTURE MECHANICS FRAMEWORK-A crack growth criteria-Deterministic : no need to create a singularity, it pre-exists-Criteria : at which condition this singularity can move

Singular area( ) ( )σ r , θ = rλ fθSharp corner (angle 90°), bi-materialTheoretical value (Bogy) : λ=-0.42

Singular area( ) ( )σ r , θ = rλ fθSharp corner (angle 90°), bi-materialTheoretical value (Bogy) : λ=-0.42Sharp corner (angle 90°), bi-material+ plasticity in copper+ finite thicknessesOrder of the singularity from FE λ=-0.5« Generalized » stress intensity factorsare determined

Singular area - approach•Assumption : Westergaard equations apply (checked by FE)•Extraction of the displacement field in the ceramic layer (elastic)•Extraction of K I and K II from this displacement field•Find the inclination α from the interface plane that maximisesK*I( α ) = C ( ) ( ) 11 α K I + C12α K II*K I( )αK*II( α ) = C ( ) ( ) 21 α K I + C 22 α K II•IfK * α max >I( ) K IC•the ceramic layer is broken along a plane inclined by an angle αmax

Summary-Singular area : the stress intensity factor amplitude increasesduring the overload cycles but then is reduced duringsubsequent fatigue cycles-Non-singular area : the failure probability of the ceramicincreases during the overload cycles but then is reduced duringsubsequent fatigue cycles

Thèse Sylvain Pietranico : année 2• Etude du comportement des métallisations souscontraintes thermiques de forte amplitude• Essais de vieillissement accélérés, évolutions de paramètresélectriques liés au vieillissement.• Observation MEB du comportement de la couche de métallisationen cours de vieillissement• Modélisation, compréhension des mécanismes de vieillissement.

Essais de vieillissement accélérés :Régimes de court-circuitEssai de court circuit:Tcc=20µsE=300VIcc=80AEnergie dissipée =0,48J

Dedicated package from MicrosemiObjectives : to analyse the ageing of :- the metallization layer- the bond wires (contacts between wires and metallization)Dedicated modules have been realised by Microsemi(600V NPT IGBT and COOLMOS TM )

Caractérisations régulières effectuées :1. Variation des caractéristiques électriques du MOSChute de tension à l’état passant, tension de seuil, courants de fuite…2. Observation MEB du MOSVue descellulesen coupeVuede la surfacesupérieurede la métallisation3. Corrélation entre la détérioration physique de la puce et la dégradationdes caractéristiques électriques du MOS

Travaux en cours: Variation des caractéristiquesMesure de Rdson, transconductance, Idsat, Vth.Variations observées : Courant de saturationVgs (mV)

Travaux en cours: Mesure de résistivitéIVI (A)3.532.521.510.500 cycle29000cyclesNombresde cycles0.E+00 1.E-03 2.E-03 3.E-03 4.E-03 5.E-03 6.E-03 7.E-03V (V)R/R01.091.081.071.061.051.041.031.021.0110.990 2000 4000 6000 8000 10000 12000 14000E (J)Chute de la conductivité de la couche de métallisationLors de la répétition des cycles de court-circuit

Travaux en cours: Observation MebNeuf1000 cycles3000 cycles7000 cycles

Travaux en cours: Observation Meb11000 cycles15000 cycles21000 cycles29000 cycles

Travaux futurs : Métallisation• Corrélation entre la dégradation de la métallisation et les propriétés électriques des modulesde puissance.• Caractérisations mécaniques de la couche d’aluminium• Réalisation d’éprouvettes par le LAAS• Observation MEB en fatigue, comparaison aux résultats obtenus lors de contraintes d’originethermomécaniquesGéométrie d’uneéprouvetteMasque des éprouvettes(2 wafer Si sont encours de réalisation)µmachine de traction

ThématiquescalculsAcknowledgementsFrench Research Agencies (DGA and CNRS)Farman institute of the Ecole NormaleSupérieure de Cachan.