silicon nitride substrates for power...
TRANSCRIPT
Silicon Nitride Substrates for Power Electronics
Ulrich Voeller, Bernd Lehmeier
2
Table of content Si3N4
Material characteristics1
2
3
4
Technology - comparison AMB/DBC
Interfacial structure and chemistry
Performance- metallized substrate
5 Summarized
3
Mechanical characteristics
Al2O3 96% AlN ZTA (9%)(HPS9%)
Si3N4
Thermal conductivity[W/mK] 24 180 28 90
Bending strength[MPa] 450 450 700 650
Fracture toughness[MPa / ] 3,8-4,2 3-3,4 4,5-5 6,5-7m
Advantage:
high reliability (thermo shock resistance) besides good thermal performance
4
Electrical characteristics
Ceramic material
Thickness [mm]
ε r (50Hz)tan δ
(50Hz)*10-3
Breakdown voltage
[kV]
Normed Breakdown voltage [kV/mm]
Partial discharge
E=14kV/mm
Si3N4 0,32 7,62 2,26 14,85 ±4,46% 46,4 <5pC
ZTA 9% (HPS 9%) 0,32 10,32 1,67 11,86±
3,27% 37,1 <5pC
AlN 0,63 8,7 1,76 21,16 ±2,82% 33,6 <5pC
Average values of N=10 Partial discharge free
5
Si3N4 Technology
Si3N4Copper
Coating
Tempering
Laser, Plating (Ni,Au/ Au/ Ag )
Copper Brazing-solder
Screen printing
Brazing process
Masking, Copper etching
2nd Etching
Si3N4
Active Metal Brazing Direct Bond Copper
DBC process
Oxidation
Masking, Copper etching
Laser, Plating (Ni,Au/ Au/ Ag )
6
Interfacial structure Si3N4 DBC
Cross section: Cu/Si3N4-100x:Sample preparation:Ion beam etching„Cross Section Polishing“
Analysis of cross section:
HR (high resolution)-SEM
Cu Si3N4
7
Interfacial structure Si3N4 DBC
Cross section: Cu/oxidation-layer/Si3N4 -20kx:
Si3N4
Cu
Oxidation layer
• thickness: 1-2µm• chemical adhesion: Copper silicate
Explanation:
Passivation of the Si3N4surface
Activation of the surface forDBC process
8
Interfacial structure Si3N4 AMB
Cross section: Cu/Brazing/Si3N4- 100x / 10kx
Si3N4
Brazing
Copper
chemical adhesion: Intermetallic compound
5000200010010
99
90807060504030
20
10
5
32
1
Cycles
Perc
ent
3,85392 35,16 1,2434,66993 56,94 1,1598,06937 109,99 15,6245,13231 2370,46 1,846
Shape Scale A D*Table of Statistics
AlN: 35 cyclesAl2O3: 55 cyclesHPS9%: 110 cyclesSi3N4 DBC: 2300 cycles
Ceramic material
Reliability [-55-150°C]
Arbitrary Censoring - ML EstimatesWeibull - 95% CI
9
Performance: Reliability
Si3N4 AMB: 5000 cycles
Comparison ceramics:
ΔT=205K (-55-150°C)
d(Cu)=0,3mm; d(Al2O3;HPS9%;Si3N4)
=0,32mm d(AlN)=0,63mm same Layout no Dimple- Design
Best Perfomance: Si3N4 DBC (Cu 0,3):
2300cycles Si3N4 AMB (Cu 0,5):
>5000cycles
10
Failure mode: DBC
Start 75 cycles50 cycles25 cycles 100 cycles
HPS9%:Start 1000 cycles 2000 cycles1500 cycles500 cycles
Si3N4:
gradual delamination of Copper, Si3N4 ceramic is staying undamaged! conchoidal fracture in HPS 9% ceramic
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comparison – thermal cyclingCombination Copper
Layoutside [mm]Ceramic
[mm]Copper Backside
[mm]Thermal Cycles
[1]
Al2O3 DBC 0.3 0.38 0.3 55HPS 9% (ZTA) DBC 0.3 0.32 0.3 110AlN DBC 0.3 0.63 0.3 35Si3N4 DBC 0.3 0.32 0.3 2300Si3N4 AMB 0.5 0.32 0.5 5000
DBC - Al2O3 cycled substrate after 50 cycles conchoidal fracture
DBC – Si3N4 cycled substrate after 2300 cycles delamination
d(Cu)=0,3mm ; d(Si3N4)=0,32mm N=9 Testing condition:continuous rise of voltage until breakdown is registered
12
Performance: Breakdown strength (DBC)
XVIIIX
12
11
10
9
8
7
6
Lot
Brea
kdow
n st
reng
th [
kV]
9,19,08,9
95% CI for the Mean Breakdown strength [kV]
Breakdown strength:
>6,5 kV@ 0,3mmCu/ 0,32mm Si3N4
13
Performance: Partial discharge free (DBC)Partial discharge free :d(Cu)=0,3mm ;d(Si3N4)=0,32mm N=12 Testing condition:
Si3N4 Lot2Si3N4 Lot1
5
4
3
2
1
0
part
ial d
isch
arge
[pC
]
Boxplot of Si3N4 Lot1; Si3N4 Lot2
Proof voltage: 5kV @ 10sec
Target value: Partial discharge free: <10pC
14
Performance: Rth comparison
6_S i3N
4_DB
C_0,32
mm
5_Si3
N4_AMB_
0,32m
m
4_AlN_
0,63_
mm
3_HPS
9%_0
,32mm
2_Al2
O3_0,3
2mm
1_Al2O
3_0,6
3mm
0,38
0,36
0,34
0,32
0,30
0,28
0,26
0,24
0,22
0,20
Material
Rth
[K/
W]
0,2010,2020,197
0,2710,275
0,359
Rth [K/W]
PelPel = 50 W = const. T1 = 100 ± 0,1 °C = const. Solder: SnAg3,7Cu0,7
(d=0,05mm)
15
Summary
ProcessTechnology
Direct Bonded Copper (DBC) Active Metal Brazing (AMB)
Reliability 2300 cycles >5000 cycles
Materialcombination(Cu/Si3N4/Cu)
0,3/0,32/0,3 0,5/0,25/0,50,5/0,32/0,5
Partial dischargefree
++ ++
Design Rules Standard DBC Design Rules: min spacing: 0,5mm @ 0,3mm Cu
AMB Design Rules: min. spacing: 1mm @ 0,5mm Cu
Cost +20%
16
comparison – summary
The increasing demand for longer life time cycles and higher thermal performance in power modules can be realized with high strength Si3N4 insulating material.
The investigation showed that depending on the metallization method, the reliability of Si3N4 was better by a factor of 20 using DBC (direct bond copper) technology and by a factor of 50 using AMB (active metal brazing) technology compared to conventional DBC ceramic materials.
The higher mechanical properties of Si3N4 ceramic, especially its very high fracture toughness (K1C), contribute to its enhanced reliability.
Furthermore, Si3N4‘s higher strength enables the use of a thinner cross section resulting in a comparable thermal performance to AlN.
Thank you for your attention