SOP

Electromigration study in eutectic SnPb solder

joints with Ni under-bump-metallization and

solder-on-pad surface finish

SOP

Electromigration study in eutectic SnPb solder joints with Ni under-bump-metallization and solder-on-pad surface finish

Student Tai-Lin Wu

Advisor Chih Chen

A Thesis

Submitted to Department of Materials Science and Engineering

College of Engineering

National Chiao Tung University

in partial Fulfillment of the Requirements

for the Degree of Master in

Material Science and Engineering

August 2009

Hsinchu, Taiwan, Republic of China

I

SOP

SOP(solder on pad)

II

Electromigration study in eutectic SnPb solder joints

with Ni under-bump-metallization and solder-on-pad

surface finish

Student: Tai-Lin Wu Advisor: Dr. Chih Chen

Department of Materials Science and Engineering, National Chiao

Tung University

Abstract

As the performance and device density of electronic products continuous to

increase, electromigration has become an important reliability issue.In this study,

electromigration study is conducted in eutectic SnPb solder joints with Ni

under-bump-metallization and solder on pad (SOP) surface finish. We observed that

there is severe damage on the substrate side, and the damage on chip side is not

obvious. The damages on substrate side included void formation, dissolution of

copper, and intermetallic compound formation. The voids almost separated Cu pad

from the solder. We used microstructure analysis and 3-dimension simulation to

investigate the electromigration mechanism in the area between SOP/ Cu surface

finishes and solder. The higher diffusion rate of Cu in the eutectic SnPb solder was

responsible for the serious void formation in the surface of the SOP and the solder

layers. Therefore, the surface becomes the weakest region during electromigration.

III

CC lab

IR ppp

FIB

chear

IV

I AbstractII ..III ..IV ..VI ..1 1-1...1 1-2...3 ..6 2-1 ......6 2-2 ..7 2-2.1 ....7 2-2.2 8 2-2.3 8 2-2.4 TCR ..9 2-3 10 2-3-1 ...10 2-3-2 .11 2-4 ...12 UBM ..12

2-5 ...13

.22 3-1. ..22 3-2. ..23 3-2-1. 23 3-2-2. TCR effect .24 3-2.3 ..24 3-3 ...25 30 4-1 ..30 4-1.1 ..30 4-1.2 ..32 4-1.3 ...34 4-1.4 semi in-situ ...37 4-2 ..38 4-3 ...39

V

. ..56 ... ..57

VI

1-1 ..5 1-2 ..5 1-3 Kelvin structure .6 2-1 [9].14 2-2 [10].15 2-3 [12]16 2-4 (a)[14].....17 2-4 (b) 0.59 IR [14]..17 2-5 (a)-(c) 125 2.25 104 A/cm2 SEM [15]18 2-6 (a) IMC (b) [16].19 2-7 [1718].20 2-8 (a)5m 2.25 104 A/cm2 (b) 10m 3 104 A/cm2 100 100 (c) 50 m 6.75 104 A/cm2 100 100 [2122]21 3-1 ....26 3-2 TCR ...27 3-3 ....27 3-4 EDS ..28 3-5 ...29 4-1 ....41 4-2 130, 1.6 A 607 ..41 4-3 100, 1.6 A 1443 (a) SEM (b) SEM ....42 4-4 (a) 100 1.6 A 1164 OM (b) 43 4-5 130, 1.6 A 525 ..44 4-6 130, 1.6 A 525 (a) SEM (b) SEM ..45 4-7 100, 1.6 A 1164 (a) SEM (b) SEM ...46 4-8 100 1.6 A ..47 4-9 100 0.8 A semi in-situ (a) SEM (b) SEM ..48

VII

4-10 ..49 4-11 TCR .....50 4-12 ..51 4-13 ..51 4-14 .....................................................52 4-15 (a) (b) ....................................................................................................................53 4-16 (a) (b) ................................................................................................54

1

1-1.

1-1 [1]IC

(Chip to Module)

(Module

to Board)

(Board to Mother Board)

I/O

(Peripheral Array)

(Area Array)

I/O

(Self-Alignment)IBM 1960s

2

C4 ( Controlled Collapse Chip Connection )[2] 1-2

(Solder Bump)

(Sn63Pb37 183 )

(Spalling)

2006

(RoHS)[3]

[4]2005

Pb210Pb206Bi

Soft Error

3

1-2.

( Organic Solderability

PreservativeOSP) ( Solder on PadSOP)

( Electroless Nickel immersion GoldENIG)( HASL )

( Immersion Silver)( Immersion Tin) SOP

( pre-solder )

Au / Ni SOP

ENIG

( Intermetallic compound

IMC)

4

5

1-1

1-2

6

2-1

20

1994Skaupy Electron Wind

K. N. Tu

2003JAP[5]

Paul S. Ho

Thomas Kwok[6]Seith Wever

Nernst-Einstein

* *0 exp( )

Ne Ne QJ Z jD Z jDkT kT kT

= = (2-1)

)exp(0**

kTQjDZ

kTNejDZ

kTNeJ == (2-1)

JTZ*

D0Q Blech

10, 3, 1m164966 nmh

7

0.73 0.12 eV [78]

Kuo Ning Chiang, Chien Chen Lee APL2006

[9]

2-1

Blacks Equation

1 exp( )nQMTTF A

j kT= (2-2)

ln( ) ln ln QMTTF A n JkT

= + (2-3)

2-2

2-2.1

D. Gupta, K. Vieregge [10]210Pb 113Sn

120 120

2-2(a)400 K Arrhenius

Pb Tracer Sn Tracer 84.8 kJmol

77 kJmol Di0 710-10 m3s 710-12 m3s

8

150 mJm2 400 K Di0

Arrhenius

2-2(b)

2-2.2

Jong-Kai Lin, Jin-Wook Jang [11]UBM

150 5.1 104 30

IMC

2-2.3

9

Everett C. C.[12]

2-3

2-2.4 TCR

James Prescott Joule1841[13]

qV

V=IR()

P=I2R=J2V (2-4)

P I R J V

10

1 A

TCR

(Temperature Coefficient of Resistance effect)

TCR=01

10 TTRRoRf

(2-5)

S.H. Chiu [14]

2-4

TCR

2-3

2-3-1

Everett C. C. Yeh,[15]Al/Ni(V)/Cu

UBM1m1252.25 104 A/cm2

UBM

11

2-5

K. N. Tu [16]95.5Sn4.0Ag0.5Cu

Al/Ni(V)/Cu UBM 2-6 146

3.67103A / cm2 15%

6

2-3-2

Y. H. Lin, C. M. Tsai, Y. C. Hu, Y. L. LinC. R. Kao

J.Mater. Res. 182003[17]J. Electron. Mater. 342005[18]

5 m

100 2104 Acm2

2-7

12

C. Y. Liu, Lin Ke, Y. C. ChuangS. J. WangJAP, Vol. 100

2006[19]

2-3-3

M.H. Chu Chih Chen 2008 [20]

SOP

2-4

UBM

Jae-Woong Nah[21,22] 510 50 m

20 m (2-8)

13

50 m

50 m

(MTTF)10 20 m

2-5

H.Y. Hsiao Chih Chen APL 2009 [23]

()

14

2-1

1431 1.68 104 A/cm2 SEM

[9]

15

(a) (b)

2-2 [10]

16

2-3 [12]

17

(a)

2-4 (a)

(b) 0.59 IR

[14]

18

2-5(a)-(c) 125 2.25 104 A/cm2

SEM(d)(a)-(c)[15]

19

2-6 (a) IMC (b)

[16]

20

2-7 [1718]

21

(a)

(b)

(c)

2-8 (a) 5 m 2.25 104 A/cm2 (b) 10 m

3 104 A/cm

2 100 100 (c) 50

m 6.75 104 A/cm2 100 100

[2122]

22

3-1.

3-1 UBM under-bump

metallization Ti / Cu / Ni 0.1 m / 0.5 m / 2

m Ti / Cu Ni

100 m 110 mUBM

( Contact Opening ) 90 m

( UBM Opening ) 110 m 65 m

1.5 m( Pitch ) 270 m

(Presolder) FR4

20 m

23

3-2.

3-2-1.

Keithley 2400

Data switchAgilent E34970A

Agilent E34901A 90 100

mV 5V

()

135 m 2.2~2.5

106 V5V

GPIB

LabVIEW

24

3-2-2. TCR effect

TCR ( Temperature Coefficient of

Resistance )

0.2

5025175

3-2 TCR

0.2 IR ( Infrared Scope )

1

TCR

3-2.3

3-3 120

600120025004000 SiC

25

10.30.05m

(SEM)

JEOL 6500 (SEM)(OM)X

(EDSEnergy Dispersive Spectroscopy)

EDS 3-4

(Cu,Ni)6Sn5

3-3

3-5ANSYS

(mesh)

1.6

26

105 m

90 m

Cu (20 m)

eSnPb

Ni (2 m)Cu (0.5 m)Ti (0.1 m)Al (1 m)

3-1

27

3-2 TCR

3-3

28

Element Atomic%Ni 15.67Cu 45.21Sn 39.12

(Cu,Ni)6Sn5

3-4 EDS

29

3-5

30

4-1

4-2

4-3

4-1

4-1.1

4-1

4-1

SEM

(Ni,Cu)3Sn4 (Cu,Ni)6Sn5

31

Cu6Sn5

4-2 607 1.6

130

(Polarity Effect)

4-2

4-3(a)100

1.6 A 1443

32

4-3(b)

4-4(a) 100

1.6 1164

4-4(b)

4-1.2

4-5 130

1.6 525

EDS UBM

(Ni,Cu)3Sn4 UBM (Cu,Ni)6Sn5

33

(

()

)

SEM

1. ( 220

0.18 wt%)

2. 0.5 um

Cu6Sn5 2 um

Ni3Sn4

3. ( = UBM opening (110 um)=

bump height (105 um) )

4-1

2/13/1 )()(Asolder

AcuVsolder

Vcu= --(4-1)

34

V A

Cu6Sn5

5% [24] Ni3Sn4 10.7%

[24]

A Cu6Sn5,Cu pad = 317.6 (um2) A Ni3Sn4 = 1921.4 (um2)

A Cu6Sn5,Cu film= 603.9 (um2)

Atotal = A Cu6Sn5,Cu pad + A Ni3Sn4 + A Cu6Sn5,Cu film = 2842.9 (um2)

AIMC = 2140 (um2)

SEM

SEM

4-1.3

4-6 130 1.6 525

35

SEM Passivation Opening

2.52 104 / 4-6(a)

4-6(b)

(Ni,Cu)3Sn4 (Cu,Ni)6Sn5

4-6(b)

4-7 100 1.6 1164

SEM 4-7(a)

SEM

36

4-7(b) SEM

130

4-5(b) 4-6(b)

Spalling

100 130

1.6 10

37

1000 / cm 4-8

4-1.4 Semi In-situ

Dasiy-chain

Semi In-situ

4-9(a) 130

0.8 A Passivation Opening 2.5104

/ 4-9 (a)

(Hillock)

4-9 (b)

38

BEI Hillock

Hillock

130

4-10

4-2

(183)

39

TCR

TCR

50 175( 25)

4-11

R = 81.17573 + 0.30953 Temp.

4-3

ANSYS 4-12

1.6

4-12

( 1)

63178 /

40

3 4 19881 /

15473 /

1 2

10 3 4

1.3

4-13

1 21215 / 2

14824 /

4-12 3 4 4-12

1 2

4-14

25418 /

41

4-15 (a)

4-15 (b)

4-16 (a)

,

4-16 (a). 4-16 (a)

, 4-16 (b)

42

4-1

e

4-2 130, 1.6 A 607

43

e(a)

e

(b)

4-3 100, 1.6 A 1443

(a) SEM

(b) SEM

44

(a)

First cross-section plane

Second cross-section plane(b)

void

4-4

(a) 100 1.6 A 1164 OM

(b)

45

Element

Sn

Totals

(Ni,Cu)3Sn4

(Cu,Ni)6Sn5

e

4-5 130 , 1.6 A 525

46

e(a)

e(b)

4-6 130, 1.6 A 525

(a) SEM

(b) SEM

47

e(a)

e(b)

4-7 100, 1.6 A 1164

(a) SEM

(b) SEM

48

4-8 100 1.6 A

49

e(a)

e(b)

4-9 100 0.8 A semi in-situ

(a) SEM

(b) SEM

50

Chipside

TMTM

EM

Substrateside

EM

e

e ePbSn Sn Pb

TM

EM

TM

EM

4-10

51

4-11 TCR

52

34

12

1 2 3 4current density

(A/cm2) 63178 6106 19881 15473

4-12

1 2

1 2current density

(A/cm2) 21215 14824

4-13

53

4-14

54

4-15 (a) (b)

55

4-16 (a)

(b)

56

57

1. Intel Technology Journal, 9, 4, (2005). 2. V. B. Fiks, Soviet Physics Solid State, 1, pp.14-28, (1959). 3. European Union Waste in Electrical and Electronic Equipment (WEEE)

Directive, 3rd Draft, May (2000). 4. Japanese Ministry of Health and Welfare Waste Regulation on

Un-Reusable Pb, June (1998). 5. K.N.Tu, Recent advances on electromigration in VLSI of interconnects,

J. Appl. Phys, 94, pp. 5451-5473, (2003). 6. P. S. Ho and T. Kwok, Rep. Prog. Phys., vol. 52, pp. 301-348, (1989). 7. I. A. Blech and C. Herring, Appl. Phys. Lett. 29, 131,(1976).

8. T. L. Shao, S. W. Liang, T. C. Lin, and Chih Chen,WEEEDirective,

3rd Draft, May (2000).

9. Y.L.LIN, Y.S. LAI, C.M. TSAI, and C.R. KAO Journal of ELECTRONIC MATERIALS, Vol. 35, No. 12, (2006).

10. D. Gupta, K. Vieregge, and Gust, V.47, No. 1, pp.5-12, (1999). 11. J. K. Lin, J.W. Jang, and Jerry White, ECTC (2003).pp.816-821. 12. C. C. Yeh, W. J. Choi, K. N. Tu, P. Elenius, and H. Balkan, Appl. Phys.

Lett. Vol. 80, 580, (2002). 13. Joule, J.P. Philosophical Magazine, Vol. 19, PP. 260; Scientific Papers

65(1841). 14. S. H. Chiu, T. L. Shao, and Chih Chen, Appl. Phys. Lett.88,022110,

58

(2006). 15. E. C. C. Yeh, W. J. Choi, and K. N. Tu, P. Elenius, and H. Balkan,

Appl.Phys. Lett. Vol.80, Issue4, pp. 580-582 (2002). 16. Lingyun Zhang, Shengquan Ou, Joanne Huang, K. N. Tu, Stephen

Gee and Luu Nguyen, Appl. Phys. Lett. Vol.88, Issue, 012106 (2006). 17. H. Lin, C. M. Tsai, Y. C. Hu, Y. L. Lin, and C. R. Kao, J.Electron.

Mater. Vol. 34, 27, (2005). 18. C. Hu, Y. H. Lin, C. R. Kao, and K. N. Tu, J. Mater. Res. Vol. 18,

2544, (2003). 19. C. Y. Liu, Lin Ke, Y. C. Chuang, and S. J. Wang, JAP Vol. 100,

083702, (2006). 20. M.H. Chu and Chih Chen, Failure mechanism in SnCu solder bumps

with Al/Ni(V)/Cu thin-film UBM and OSP surface finishes (2008) 21. Jae-Woong Nah, J. O. Suh, and K. N. Tu, Seung Wook Yoon, Vempati

Srinivasa Rao, and Vaidyanathan Kripesh and Fay Hua J. Appl. Phys. Vol.100, Issue 12, 123513 (2006).

22. Jae-Woong Nah, Kai Chen, J. O. Suh, and K. N. Tu, ECTC (2007)

pp. 1450-1455. 23. H.Y. Hsiao and Chih Chen, Appl. Phys. Lett. 94, 092107 (2009). 24. Howard D. Blair, Tsung-Yu Pan, John M. Nicholson, ECTC (1998)

pp.259-267.