Influence of thermal cycling on shear strength of Cu –

Sn3.5AgIn – Cu joints with various content of indium

 

Pavol Šeboa, Peter Švecb, Dušan Janičkovičb, Pavol Štefánika

 

a Institute of Materials and Machine Mechanics, SAS, Račianska 75, 831 02 Bratislava, Slovakia

b Institute of Physics, SAS, Dúbravská cesta 9, 845 11 Bratislava, Slovakia

institute of materials & machine mechanics slovak academy of sciences

Subject of study

Published results

Aim of this contribution Conclusions

COST 531: Lead-free solder materials:

From many material combinations for study of

low temperature lead-free solder

we chose

on the base of literature data

Sn-Ag based alloys

Subject of study

To characterize the effect of indium effect of indium additionaddition in lead-free Sn – 3.5 Ag solder on its

phase transition temperature,

wetting of copper substrate

shear strength of copper joints.

Part of the results were presented at Part of the results were presented at

the COST 531 meetings in Lausanne the COST 531 meetings in Lausanne

and Genoaand Genoa

Most of the results were published in Most of the results were published in

Kovove Mater. 43 (2005) 202-209Kovove Mater. 43 (2005) 202-209

Published results

Solder Sn3.5Ag

Sn3.5Ag6.5In

Sn3.5Ag9In

225 209 206

Hm[J/g] 67 60 61

Txf[°C] 192 182 181

Hf[J/g] -64 -59Txm – Txf

[°C]33 27

Txm[°C]

-60

25

HHmm, , HHff , T , Txmxm, T, T

xfxf are for enthalpy changes and are for enthalpy changes and

onset temperatures of melting and fronset temperatures of melting and freeezing of ezing of relevant solders, respectivelyrelevant solders, respectively

Differential scanning calorimetry

Indium concentration dependence of contact angle Indium concentration dependence of contact angle of solders on Cu substrate for various temperaturesof solders on Cu substrate for various temperatures

250 280 320

0

10

20

30

40

50

60

70co

nta

ct a

ng

le [

° ]

temperature [°C ]

9 In [wt.%]6.5

0

0

5

10

15

20

25

30

35

250 280 320 250 280 320 250 280 320

temperature [°C]

shea

r st

ren

gth

[M

Pa] Sn3.5Ag Sn3.5Ag6.5In Sn3.5Ag9In

Shear strength of Cu-solder-Cu jointsShear strength of Cu-solder-Cu joints

Sn3.5Ag6.5InSn3.5Ag6.5In280°C, 30 min.280°C, 30 min.

compositecomposite

Cu foilCu foil

Cu-solder-CuCF composite joint

0

5

10

15

20

25

30

35

sh

ea

r s

tre

ng

th [

MP

a]Sn3.5Ag6.5InSn3.5Ag

280 °C30 min.

Shear strenght of Cu-solder-CuCF composite joint

•Indium decreases the onset temperature and Indium decreases the onset temperature and etnhalpy changes of melting and freezingetnhalpy changes of melting and freezing

• Wetting angle between copper substrate and Wetting angle between copper substrate and SnAgIn solder decreases with increasing amount SnAgIn solder decreases with increasing amount of of In and wetting temperature and timeIn and wetting temperature and time

• Joint strength moderately decreases with Joint strength moderately decreases with increasing joining temperature and the amount of In. increasing joining temperature and the amount of In. Failure of joints occureFailure of joints occuress in solder. in solder.

• Joint stregth of Cu-CF composite is lower than Joint stregth of Cu-CF composite is lower than that of Cu-Cu due to poor adhesion betweenthat of Cu-Cu due to poor adhesion between Cu and Cu and CF layer where the failure is occured.CF layer where the failure is occured.

Conclusions

The aim of this paper is:

•    to recognize the microstructure changes in Sn-3,5Ag solders and joints of Cu-Cu

• to identified the intermetallic compounds in the Cu – solder – Cu pad interfaces

•to determine the effect of thermal cycling on the degradation in residual shear strength of Cu – Sn-3.5Ag-In – Cu joints

•with various amount of indium.

Materials

Solders: Lead-free solder alloys contained: 0 (1); 6.5(2) and 9(3) mass % In  Produced in bulk form (for wetting experiments) and by rapid quenching in the ribbon form 5 mm wide and ~0.05mm thick (for Cu-solder-Cu joints) 

Substrates: Cu plates prior to placing with solder into the holder and furnace were daubed with rosin moderately activated flux.

Joints:

Joints-four for each set of cycling-were prepared at 280°C and 1800 s in the air atmosphere:

 One specimen was used for microstructure study, three for shear strength measurement

  Cycling:

Cycling was done in air atmosphere in the temperature interval: RT – 150°C;

 Number of cycles: 100; 200; 500 and 1000. Also in interval: RT-180°C : 500 cycles

Investigation (of solders, joints, interface in joint): 

Microstructure: light and scanning electron microscopy (SEM), energy disperse X-ray analyzer (EDAX),

X-ray diffraction (CuK radiation)

  Influence of thermal treatment on solders:

Resistometry: planar furnace with 4 probes method

 Shear strength: Zwick testing machine, push-off method

Results

Microstructure of original solders:

Solder Sn-3.5AgSolder Sn-3.5Ag

Solder Sn-3.5Ag-6.5 InSolder Sn-3.5Ag-6.5 In

Solder Sn-3.5Ag-9InSolder Sn-3.5Ag-9In

30 40 50 60 70 80 90

SnAg3SnIn4Ag9InSn4

In 9

In 6.5

In 0in

tens

ity

2 theta [deg]

X-ray phase analyssis of Sn-3.5Ag solders with InX-ray phase analyssis of Sn-3.5Ag solders with In

In 6.5In 6.5

In 9In 9

In 0In 0

50 100 150 2001.0

1.5

2.0R

(T)/

R(R

T)

temperature [deg. C]

In 0 In 6.5 In 9

Temperatuture dependence of the resistance of Temperatuture dependence of the resistance of the Sn-3.5Ag solder with Inthe Sn-3.5Ag solder with In

All three solders heated All three solders heated

In0 In0 – up to 180 °C– up to 180 °C

In6.5 In6.5 – up to 160 °C– up to 160 °C

In9 In9 – up to 180 °C– up to 180 °C

and quenchedand quenched

X-ray diffraction : X-ray diffraction : No change in phase No change in phase compositioncomposition

SEM: SEM: coarsening of microstructure in coarsening of microstructure in In6.5 and In9In6.5 and In9

0

5

10

15

20

25

0

10

0

20

0

50

0

10

00 0

10

0

20

0

50

0

10

00 0

10

0

20

0

50

0

10

00

number of cycles

shea

r st

reng

th [M

Pa]

Sn3.5Ag Sn3.5Ag6.5In Sn3.5Ag9In

Shear strengths of the Cu-solder-Cu jointsShear strengths of the Cu-solder-Cu joints

CuCu66SnSn55 between Cu-Sn3.5Ag solder after between Cu-Sn3.5Ag solder after

uncyceld (a) and 1000 cycles (b)uncyceld (a) and 1000 cycles (b)

RT – 150 °CRT – 150 °C

CuCu66SnSn55

CuCu66SnSn55 between Cu-Sn3.5Ag6.5In solder after between Cu-Sn3.5Ag6.5In solder after

uncyceld (a) and 1000 cycles (b)uncyceld (a) and 1000 cycles (b)

RT – 150 °CRT – 150 °C

CuCu66SnSn55

0

5

10

15

20

25

0

10

0

20

0

50

0

10

00 0

10

0

20

0

50

0

10

00 0

10

0

20

0

50

0

10

00

number of cycles

shea

r st

reng

th [M

Pa]

Sn3.5Ag Sn3.5Ag6.5In Sn3.5Ag9In

Shear strengths of the Cu-solder-Cu jointsShear strengths of the Cu-solder-Cu joints

Shear strength of Cu-solder-Cu joints for 100,200,500 and 1000 cycles (including shear strength of no cycled joints). 

Joints with solder (1): Shear strength decreases with increasing amount of cycles. This decrease reflects the increase of Cu6Sn5 phase thickness. 

Joints with solder (2): Shear strength increases with increasing the number of cycles and thickness of Cu6Sn5 layer decreases.

 Joints with solder (3): Shear strength increases except for 1000 cycles (where shear strength is on the level of no cycled joint). The thickness of Cu6Sn5 layer decreases with increasing the number of cycles except for 1000 cycles where InSn4 phase arises instead of In4Ag9. 

One can suppose that this phase retards the dissolution of copper from Cu6Sn5 phase.The higher is the thickness of Cu6Sn5 layer the lower is the shear strength of the joint.

The In4Ag9 phase seems to enhance the dissolution of copper from Cu6Sn5 phase into the SnAg solder.

30 40 50 60 70 80 90

(4)

(3)

(2)

(1)

2 theta [deg]

inte

nsity

CuSnCu6Sn5Ag3SnAg4SnIn4Ag9InSn4

X-ray phase analyssis of joints with X-ray phase analyssis of joints with Sn-3.5Ag solder and InSn-3.5Ag solder and In

In 6.5 1000 cyclesIn 6.5 1000 cycles

In 0 1000 cyclesIn 0 1000 cycles

In 9 1000 cyclesIn 9 1000 cycles

In 9 uncycledIn 9 uncycled

 Material

Number of

cycles

 Phases

Sn3.5Ag solder  Sn, Ag3Sn

Sn3.5Ag6.5In solder  Sn, In4Ag9

Sn3.5Ag9In solder  Sn, In4Ag9, InSn4

Cu – Sn3.5Ag – Cu joint 0Sn, Cu, Cu6Sn5, Ag4Sn,

Ag3Sn

Cu – Sn3.5Ag – Cu joint 1000Sn, Cu, Cu6Sn5, Ag4Sn,

Ag3Sn

Cu – Sn3.5Ag6.5In – Cu joint

0 Sn, Cu, Cu6Sn5, In4Ag9

Cu – Sn3.5Ag6.5In – Cu joint

1000 Sn, Cu, Cu6Sn5, In4Ag9

Cu – Sn3.5Ag9In – Cu joint

0

Sn, Cu, Cu6Sn5, Ag3Sn,In4Ag9

Cu – Sn3.5Ag9In – Cu joint

1000

Sn, Cu, Cu6Sn5, Ag3Sn, InSn4

ConclusionSn-3.5Ag-In(0;6.5;9 mass.%) solders consist of Sn and Ag3Sn; In4Ag9 and In4Ag9 and InSn4, respectively.

In all joints before and after thermal cycling in the temperature interval RT-150°C as well as RT-180°C at the interface between copper substrate and the solder Cu6Sn5 phase is formed.

For the joints made with indium-free solder the thickness of this phase is growing with increasing the number of cycles and the shear strength of these joints is decreasing.

For the joints made with In containing solders the thickness of this phase (Cu6Sn5) is decreasing with increasing the number of cycles and the shear strength of these joints is increasing.

Contents of phases in joints made with Sn-3.5Ag and Sn-3.5Ag-6.5 mass% In is equal before and after cycling

For joint with Sn-3.5Ag-9In solder after 1000 cycles InSn4 phase is formed instead of In4Ag9 phase.