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TRANSCRIPT
Die Attach Soldering
Jie Geng, Hongwen Zhang and Ning-Cheng Lee
Indium Corporation
iNEMI Solder Materials Workshop at IPC APEX, San Diego, CA 31 January, 2019
Contents
• Introduction and background
• Indium’s solder materials for different service temperature ranges:
• I. Up to 175°C: SACSb(-X)
• II. Up to 200°C: BiAgX®
• III. Above 200°C: SnSbAgCu-X
2
Bonding Materials in Power Discrete Components
3
Discrete Power Components will be bonded onto a PCB in the subsequent SMT reflow, which requires the internal Die-Attachment surviving 260oC SMT reflow temperature multiple times, and no significant degradation in the electrical and the thermal performance under service (<150oC) . High-Pb solders are still widely used and exemption has been extended to 2021.
http://powerelectronics.com/pmics/25-pol-regulator-shrinks-pcb-size-20
Bonding Materials in Power Modules
4
Power Modules require surviving the service condition without significant degradation in the mechanical, the electrical, and the thermal performance. WBG (SiC/GaN) Power Modules require a more reliable design for Tj of 150oC, 175oC and 200oC or even higher.
CSPT, 2018
Lead-Free Bonding Materials
Selection of the bonding materials depends on the requirements of the performance, the processing, and the cost of the power devices.
<150oC
<200oC
<300oC
<800oC
<500oC
iNEMI Project HTLF Bonding Materials for Die attachment, 2017 5
0 50 100 150 200 250 300
0
20
40
60
80
100
120
140
Bo
nd
Sh
ea
r S
tre
ng
th (
MP
a)
Temperature (oC)
BiAgX SiC/AMB
BiAgX Si/Cu
ZnAl SiC/AMB
AuGe SiC/AMB
AuSn SiC/AMB
SnSbCuAgX-3 Cu/Cu
Pb10Sn2Ag Capaticor
Pb5Sn1.5Ag Capacitor
Pb5Sn2.5Ag Si/DBC
Ag sintering Si/DBC
SAC305 Cu/invar
Innolot Cu/invar
Indalloy 276 Cu/Invar
High Lead
BiAgX
Press-less Ag-sintering
SnSbCuAgX
ZnAl
Au-rich
Sn-rich Solder
Potential LF Bonding Materials
LF bonding materials, Sn-rich SACSSb, SnSbCuAgX, BiAgX®, Au-based, ZnAl, and Ag-sintering materials are better in bond shear strength than high-Pb solders in certain temperature rang.
IEC
DA5
6 CSPT, 2018
I.
SACSb Solder (IND276) with High Reliability Performance up
to 175C
7
Shear test and thermal ageing at 175°C
Cu die (3mm x 3mm) on Alloy42 substrate
• At high temperature, SACSb is more ductile than both SAC305 & SACBSbN
• SACBSbN is very brittle.
8
SACSb ~ 2.5X of SACBSbN
Performance under temperature cycling
FB FA
After 3000 cycles, SACSb was 11-20X of SACBSbN and SAC305
FB FA
Harsh condition SACSb >> SACBSbN > 305 FA ≥ FB
9
Summary of SACSb
• Both SACSb and SACBSbN are alloys based on SnAgCu, but
reinforced with precipitate hardening and solution hardening. SACSb exhibited a finer microstructure with less particles dispersed, while SACBSbN exhibited more particles with some blocky Ag3Sn plates or rods. SACSb is strong and ductile, while
SACBSbN is strong but brittle.
• Under the harsh test condition where T was high, the dimension mismatch between parts and substrate became very significant due to CTE mismatch. This significant dimension mismatch would cause a brittle joint to crack quickly, as seen on SACBSbN. The challenge was more tolerable for a ductile joint, as shown by SACSb.
• Overall, to achieve high reliability under a wide service temperature environment, a balanced ductility and strength for solder alloy is critical for success.
• Targeted at Tj=150oC~175oC power module
10
II. High Temperature
Performance of BiAgX®
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BiAgX® - TCT Performance
0 500 1000 1500 20000
10
20
30
40
50
Bo
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MP
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Cycle # of TCT
BiAgX SiC/CuMo -55~200oC [1]
L-BiAgX Si/CuLF-55~125oC [2]
H-BiAgX Si/CuLF -55~125oC [3]
7.08 Si/Cu TST -55~150oC [4]
7.16 Si/Cu TST -55~150oC [5]
BiAgX Si/Cu TCT -40~175oC [6]
BiCuX Si/Cu TCT -40~175oC [7]
Pb5Sn2.5Ag Si/Cu TST -55~150oC [8]
Die Size
[1] 5mmx5mmx0.38mm
[2], [3] 2.5mmx2.5mmx0.32mm
[4], [5],[6],[7],[8] 3mmx3mmx0.68mm
272.09°C
279.01°C
271.52°C
272.64°C
269.98°C
274.50°C
Bi
BiCuX-1
BiCuX-2
BiCuX-3
Onset of Bi: 271.52oCOnset of BiCuX-1: 272.09oCOnset of BiCuX-2: 269.98oCOnset of BiCuX-3: 270.59oC
270.59°C
270.95°C
-8
-6
-4
-2
0
2
Heat F
low
(W
/g)
250 255 260 265 270 275 280 285 290
Temperature (°C)Exo Up Universal V4.7A TA Instruments
BiCuX
Onset Melting Temperature of BiCuX >270oC
Onset Melting Temperature of BiAgX >262oC
270oC
12
BiAgX® - Recrystallization and Fatigue
Recrystallization occurs during TCT before the fatigue crack nucleation and growth. The interior far away from the perimeter shows no obvious morphology change.
Harry Schoeller, Brittle to Ductile Transition in High Bi Solder, AREA Consortium Meeting March, 2015
Recrystallization upon TCT -55oC to 150oC
A
B-2
B-1
B-2 Recrystallization B-1
A Solder Creep Fatigue
13
Summary of BiAgX
• A drop-in lead-free solder for die attach
• Acceptable wetting and voiding
• Resisting the additional SMT reflows up to a 260oC peak temperature
• Acceptable thermal storage resistance even at 230oC
• Mechanical and thermal mechanical reliability comparable to or better than Pb5Sn2.5Ag
• Reasonable Cost
• Targeted at power discrete application
14
III. SnSbCuAg-X
15
Melting Behavior and Joint Microstructure
SnSbCuAgX (1)Solidus>300oC (2)Liquidus<360oC (3) >30MPa@ 260oC
Thermal Conductivity λSnSbCuAgX = 34 W/mK λPb92.5Ag5Sn2.5 = 23 W/mK
Patent Pending
Si (TiNiAu)
Bare Cu on DBC
(CuNi)6Sn5
SnSb
Ag3Sn
16
SnSbCuAgX - TCT Performance
0 500 1000 1500 2000 2500
0
5
10
15
20
25
30
35
40
Bo
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MP
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Cycle # of TCT
SnSbCuAgX-2 Si/DBC [1]
SnSbCuAgX-3 Si/DBC [1]
SnSbCuAgX-2 Cu/Alloy42 [2]
SnSbCuAgX-3 Cu/Alloy42 [2]
TCT -40 to 175oC 10min
[1] 3mmx3mmx0.68mm Si on bare Cu/SiN DBC
[2] 3mmx3mmx0.68mm Cu on Alloy 42
Si
Interface
Bond shear leads to Si die shattering even after TCT for Si/DBC.
DA5
IEC
17
SnSbCuAgX - TCT Performance
After 2000cycles of TCT -40 to 175oC
Si
Bare Cu on DBC
Si
Bare Cu on DBC
Si
Bare Cu on DBC
Vertical cracks are seen from Si die to DBC instead of lateral cracks around corner.
Targeted at power module application
18
Summary
• Performance of solder materials is highly dependent on the assembled components and service conditions.
• Solder alloys can be tailored by their specific applications to meet the requirements.
19
Acknowledgement
Thanks Chris LaBarbera for all the SEM work.
20
Thank you!
Questions?