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

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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

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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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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

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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

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III. SnSbCuAg-X

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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

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15

20

25

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35

40

Bo

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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

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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.

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Acknowledgement

Thanks Chris LaBarbera for all the SEM work.

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Thank you!

Questions?