sn3.5ag pb-free alloy for bga application€¦ · freescale semiconductor confidential and...

TM

Freescale Semiconductor Confidential and Proprietary Information. Freescale™ and the Freescale logo are trademarksof Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2006.

Sn3.5Ag PbSn3.5Ag Pb--Free Alloy for BGA ApplicationFree Alloy for BGA Application

Customer PresentationCustomer Presentation

Min DingPSD/TSOJuly 20, 2009 Updated

TMFreescale Semiconductor Confidential and Proprietary Information. Freescale™ and the Freescale logo are trademarksof Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2006. 1

Outline

► Background

► Component Level Characterization

► Board-level Solder Joint Reliability

► Summary


Introduction of Sn3.5AgWhat is Sn3.5Ag?

• Composition: 96.5wt%Sn3.5wt%Ag• Alternative Pb-free solder ball alloy intended for BGA applications. • No impact to customer board assembly process due to similar liquidus

melting temperature range as current solder ball alloys (Sn4.0Ag0.5Cu)

Market Trend on Sn3.5Ag• >10 years of research/application history • Sn3.5Ag is readily available from major solder alloy suppliers• Major package assembly houses are qualified with Sn3.5Ag for BGA

production


Component Level Characterization

► Evaluation Matrix and Test Vehicles

► Manufacturability

• Geometrical profile

► Mechanical Strength Test

• Ball Shear Results

• Cold Ball pull (CBP) test

Introduction

CBP test results

• Packing Drop Test

► Solderability


Evaluation Matrix• Solder Alloy: Sn3.5Ag and Sn4.0Ag0.5Cu

• Melting Point

• Sn3.5Ag: 221oC

• Sn4.0Ag0.5Cu: 217~221oC

• Ball Attach Reflow Profile

• Ramp-to-Peak profile

• 240oC peak temperature

• >230oC 20sec dwell


Test Vehicles

Supplier 30.60.529x291.0Thermally Enhanced PBGA

Supplier 1

Electrolytic Ni/Au

0.760.637.5x37.51.27TBGA

Supplier 10.660.4537.5x37.51.0TBGA

0.6

Ball Size(mm)

0.5

Pad Opening(mm)

Supplier 227x271.0PBGA

Substrate supplier

Pad FinishBody Size(mmxmm)

Pad Pitch(mm)Package Type


Manufacturability— Statistical Process Control of Ball Geometrical Profile

02468

1012

Coplanarity Ball Height Ball Diameter Coplanarity Ball Height Ball Diameter

After Assembly After Test

Cpk

SAC405

SnAg

1.67

• Sn3.5Ag and SAC405 have good process stability in ball geometry with Cpk > 1.67

• Statistical analysis shows insignificant difference between Sn3.5Ag and SAC405 in terms of co-planarity, ball height and ball diameter for all the package types tested


New Mechanical Strength Test— Ball Shear and Cold Ball Pull

Ball Shear Cold Ball Pull

• Good for testing solder ball bulk properties• Not sensitive enough for detecting

intermetallic bond strength & brittle failure• Exert mixed force (shear & tensile)• Side support from solder mask• Speed too low (<700um/s)

• Good for testing intermetallic bond strength & brittle failure

• Mainly tensile stress

• 10x faster loading speed than shear

Shear Blade Pull Jaw


Mechanical Strength Test— Ball Shear Test

Failure Modes in Ball Shear Test

• Test speed: 300um/sec

• Sample size: 40 balls/read point


Mechanical Strength Test— Ball Shear Strength

• Both Sn3.5Ag and SAC405 showed good ball shear strength with Cpk>1.67

• Sn3.5Ag has lower shear strength reflecting the lower yield strength and hardness. This could help to reduce the stress inside the solder joint during mechanical impact.

1.90

92.2

1525

1343

1856

Sn3.5Ag

1.27mm TBGA

2.41

87.4

1631

1398

1816

SAC405

2.46

64.9

1067

913

1164

Sn3.5Ag

1.0mm TBGA

2.24

86.7

1334

954.3

1286

SAC405

75.762.571.158.8Std.Dev. (g)

2.452.172.822.40Cpk

1256110713001121Mean (g)1078100612001018Min (g)1364126014511269Max (g)

SAC405Sn3.5AgSAC405Sn3.5Ag

1.0mm TEPBGA1.0mm PBGA


Mechanical Strength Test— Ball Shear Results

• Sn3.5Ag and SAC405 samples showed 100% ductile failure (Mode 1) in ball shear

• No significant difference in failure mode found between Sn3.5Ag and SAC405

1.27mm TBGA 1.0mm TBGA 1.0mm PBGA 1.0mm TEPBGA

0%0%0%

0%

1.27mm TBGA 1.0mm TBGA 1.0mm PBGA 1.0mm TEPBGA1.27mm TBGA 1.0mm TBGA 1.0mm PBGA 1.0mm TEPBGA

0%0%0%

0%

Percentage

SAC405 SAC405 SAC405 SAC405

1.27mm TBGA 1.0mm TBGA 1.0mm PBGA 1.0mm TEPBGA

0%0%0%

0%

1.27mm TBGA 1.0mm TBGA 1.0mm PBGA 1.0mm TEPBGA1.27mm TBGA 1.0mm TBGA 1.0mm PBGA 1.0mm TEPBGA

0%0%0%

0%

Percentage

SAC405 SAC405 SAC405 SAC405


New Mechanical Strength Test— Introduction to Cold Ball Pull Test

Failure Modes in CBP• CBP is a destructive test. Different failure modes are defined in Table 1

• Mode 2 (brittle failure) is the least desirable failure mode which can lead to missing ball incident

• Units with lower Mode 2 failure rate in CBP show lower missing ball yield loss in assembly and after shipping

• CBP is a highly accelerated test, the failure rate in CBP is much higher (>100x) than that in the field.

Table 1 Failure Modes in CBP


Stress Conditions

Reflow profile (Tpeak=260oC)1x, 2x, 3x, 6xMultiple Reflow

Baking at 150oC24, 48, 96,168, 504 and 1008 hours

High Temperature Storage

As-assembledT0

DescriptionStress Condition

Sample Size: For each reading point, totally 40 balls were pulled at 5mm/s. That is 8 balls per package and 5 packages per cell.


Mechanical Strength Test— Cold Ball Pull Test Results (TBGA)

• Sn3.5Ag reduces brittle failure rate significantly. No brittle failure is observed in CBP test with Sn3.5Ag spheres after assembly and test.

CBP Brittle Failure Rate - After Assembly & Test

78% 72%

0% 0%

90%96%

0% 0%0%

20%

40%

60%

80%

100%

After Assembly After Test After Assembly After Test

SAC405 SnAg

Brit

tle F

ailu

re R

ate

(Mod

e 2)

(%)

1.27mm 37.5x37.5 TBGA1.0mm 37.5x37.5 TBGA

CBP Brittle Failure Rate - Multiple Reflow

100% 100%

0% 0% 0% 0%0% 0% 0% 0%

100%100% 100%100%93% 93%

0%

20%

40%

60%

80%

100%

1x 2x 3x 6x 1x 2x 3x 6x

SAC405 SnAg

Brit

tle F

ailu

re R

ate

(Mod

e 2)

(%) 1.27mm 37.5x37.5 TBGA

1.0mm 37.5x37.5 TBGA

CBP Brittle Failure - High Temperature Storage (hours)

0% 0% 0% 0% 0%0% 0% 0% 0%10%

90% 85% 93% 88%

54%47%

100% 100% 100% 100% 100% 100%

63% 68%

0%

20%

40%

60%

80%

100%

24 48 96 168 504 1008 24 48 96 168 504 1008

SAC405 SnAg

Brit

tle F

ailu

re R

ate

(Mod

e 2)

(%

)

1.27mm 37.5x37.5 TBGA

1.0mm 37.5x37.5 TBGA


• PBGA with SAC405 shows <10% brittle failure in CBP test. This is consistent with subcon’s data

• After stressing at high temperature storage, brittle failures increase due to IMC growth

• Sn3.5Ag continues to show no brittle failure until after 504 hours HTS, and the rate is still much lower than SAC405

Mechanical Strength Test— Cold Ball Pull Test Results (PBGA)

CBP Brittle Failure Rate - After Assembly & Test

8%

0% 0% 0%1%

0% 0% 0%0%

5%

10%

After Assembly After Test After Assembly After Test

SAC405 SnAg

Brit

tle F

ailu

re R

ate

(Mod

e 2)

(%)

1.0mm 27x27 PBGA1.0mm 29x29 TEPBGA

CBP Brittle Failure - High Temperature Storage (hours)

0% 0% 0% 0% 0%13%

0% 0%

38%50%

0%0% 8%18%

8%18% 10%

75%

0%

28%

0% 0% 0% 0%0%

20%

40%

60%

80%

24 48 96 168 504 1008 24 48 96 168 504 1008

SAC405 SnAg

Brit

tle F

ailu

re R

ate

(Mod

e2)

(%) 1.0mm 27x27 PBGA

1.0mm 29x29 TEPBGA


Mechanical Strength Test— Cold Ball Pull Strength

• Sn3.5Ag shows significantly higher CBP strength than SAC405. That suggests higher mechanical robustness.

58

1872

1743

1994

Sn3.5Ag

1.0mm TBGA

75

1772

1564

1941

SAC405

1839817879Std.Dev. (g)2027210319382067Mean (g)1569187515421925Min (g)2319229122992248Max (g)

SAC405Sn3.5AgSAC405Sn3.5Ag

1.0mm TEPBGA1.0mm PBGA


Mechanical Strength Test— Packing Drop Test

• Purpose - Simulate the shock/knock during shipping

• Sample size - 60 good units / box (lot)• 2 bundles per box• 5 full trays + 1 empty cover tray (5+1)/bundle• 6 good units per tray, 4 at corners and 2 at center, dummy units for the other

pockets• Drop – 3 feet to hard surface from 10 different angles• Freescale’s current practice in production

• No missing ball should be found after 1 cycle of drops (drop from 10 angles)

2 bundles into one box

Drop from 10 different angles


Mechanical Strength Test— Tray Drop Test

• Purpose - Simulate the shock/knock in handling and shipping• Test configuration – 6 good units per lot

• 10 trays banded together• 6 good units in the 10th (bottom) tray and dummy units fill the rest of the pockets• Drop the bundles 10cm to the surface (hard material) in 5 angles shown by the red arrows• Not a production control, for engineering purpose only


Mechanical Strength Test— Packing Drop Test Results

• “Test to failure” approach - parts are dropped multiple cycles until missing ball is seen

• Test vehicle – 1.0mm, 37.5x37.5mm TBGA

1717Sn3.5AgTray Drop

22SAC405

Packing DropNo ball missing20Sn3.5Ag

33SAC405

No. of Cycle when 1st Ball

drop observed

No. of Cycles Tested

• Both Sn3.5Ag and SAC405 can meet Freescale’s current requirement – No missing ball after 1 cycle of test

• Sn3.5Ag showed considerable improvement over SAC405 in packing drop test


Solderability— Ceramic Plate Test

• No solderability failure in both alloys• Steamage: 8hrs. +/-15min + 24 hrs of baking at 125 deg.C• Reflow peak temp: 240C

1.0mm PBGA

1.0mm TEPBGA

1.27mm TBGA

1.0mm TBGA

SAC405

SAC405

SAC405

SAC405


Board Level Solder Joint Reliability

►Air Thermal Cycling (ATC) Evaluation• Test Matrix• Board Mounting Process• Results


Air Temperature Cycling— Test Matrix

Sn4.0Ag0.5Cu

Control New Alloy

Sn3.5AgSnPb2AgSolder Alloy

Air Temperature Cycling

Condition

-40~125oC

-40~125oC

27x270.50.61TEPBGA

27x270.50.61PBGA

Package size (mmxmm)

Pad Opening

(mm)

Ball Dia(mm)

Pad Pitch(mm)

PackageType


Air Temperature Cycling— Board Mounting Process

► Solder Paste• SnPbAg – SnPb Paste• SAC405 and SnAg – SAC387 Paste

► Reflow Profile• SnPbAg – SnPb board mounting profile • SAC405 and SnAg – Pb-free profile (peak temperature >230C)


Air Temperature Cycling (-40~125oC)– 1.0mm Pitch 388 PBGA (2L Substrate)

Cyc

les

to F

irst

Fai

l

• Pad pitch 1.0mm; Ball size 0.6mm; body size 27x27mm• All Pb-free alloys have similar mean-cycles-to-failure and

significantly larger than SnPbAg• Both SAC387 and SnAg showed good repeatability

Cyc

les

to 5

0% F

ailu

re

SnAgSAC387

SnPbAg

S10

1000

2000

30004000

5000

6000

7000

8000

9000

SnAgSAC387

SnPbAg

S10

1000

2000

3000

4000

5000

6000

7000

8000

100001000

99

90

8070605040

30

20

10

5

3

2

1

Cycles-to-Failure

Cum

ulat

ive

Failu

re (

%)

19.2554 5079.53 0.974 30 09.9916 8653.47 0.991 29 1

16.8491 8154.51 0.970 22 811.6398 8923.95 0.959 25 58.6615 9580.49 0.995 25 5

13.0520 8565.14 0.958 28 2

Shape Scale C orr F CTable of Statistics

SnPbAgSAC387SAC387_RptSnAgSnAg_RptSAC105

BGA Alloy

388 PBGA 1.0mm Pitch, 27x27mm Body Size - -40~125CWeibull


Liquid-to-Liquid Thermal Shock (-55~125oC)– 1.0mm Pitch 388 PBGA (2L Substrate)

• Pad pitch 1.0mm; Ball size 0.6mm; body size 27x27mm

100001000100

99

90

8070605040

30

20

10

5

3

2

1

Cycles-to-Failure

Cum

ulat

ive

Failu

re (

%)

4.30464 3518.53 0.907 28 03.82345 5958.10 0.980 23 72.26991 4018.90 0.980 29 15.57965 5852.72 0.994 23 72.18499 6245.22 0.972 22 8


SnPbAgSAC387SAC387_RptSnAgSnAg_Rpt

BGA Alloy

PBGA 1.0mm Pitch, 27x27mm Body SizeLiquid-to-Liquid Thermal Shock -55~125C


Air Temperature Cycling (-40~125oC)– 1.0mm Pitch 516 TEPBGA

Cyc

les

to F

irst

Fai

l

• Pad pitch 1.0mm; Ball size 0.6mm; body size 27x27mm• Compared with SAC387, Sn3.5Ag similar 1st failure cycles, larger mean-cycles-to-failure• Both SAC387 and SnAg showed good repeatability

SnAgSAC387

SnPbAg

0

500

1000

1500

2000

2500

3000

3500

4000

SnAgSAC387

SnPbAg

0

1000

2000

3000

4000

5000

6000

7000

Cyc

les

to 5

0% F

ailu

re

100001000

99

90807060504030

20

10

5

3

2

1

Cycles-to-Failure

Cum

ulat

ive

Failu

re (

%)

15.8437 3302.58 0.945 31 111.3770 5034.43 0.963 32 015.6748 4563.81 0.972 32 08.0967 6238.57 0.990 32 09.2030 6599.86 0.979 31 1


SnPbAgSAC387SAC387_RptSnAgSnAg_Rpt

BGA Alloy

TEPBGA 1.0mm Pitch, 27x27mm Body Size - -40~125CWeibull


• Sn3.5Ag showed similar life of cycles as SAC387

Cycles-to-Failure

Perc

ent

100000100001000100

99

90

807060504030

20

10

5

3

2

1

Table of Statistics

14 26.09270 4554.73 0.974 16 06.93027 5330.58 0.978

Shape

16 0

Scale Corr F C6.83572 2351.75 0.938

Variable

SnAg

SnPbAgSAC387

TEPBGA 1.0mm Pitch, 27x27mm Body Size - Varied AlloysLiquid-to-Liquid Thermal Shock (-55~125C)

Liquid-to-Liquid Thermal Shock (-55~125oC)– 1.0mm Pitch 516 TEPBGA


Mechanical Bend Test– IPC-9702 Monotonic Bend Test


Mechanical Bend Test– Example Bend Test Board Top


Mechanical Bend Test– 4 Point Bend Fixture


Mechanical Bend Test– Example Strain and Resistance Versus Time


Mechanical Bend Test– TBGA Weibull Plot for Break Strain

• Sn3.5Ag showed similar break strain as SAC405

Break Strain (microstrain)

Cum

ulat

ive

Failu

re (

%)

100001000

99

9080706050403020

10

5

32

1

17.8148 5850.06 0.920 3 011.7112 5904.42 0.969 5 022.1653 5439.52 0.897 5 0

Shape Scale Corr F CTable of Statistics

SnPbAgSAC387SnAg

Variable

1.27mm Pitch, 37.5x37.5mm TBGA Varied AlloyIPC - 9702 Monotonic Bend Test

Break Strain (microstrain)Cu

mul

ativ

e Fa

ilure

(%

)

100001000

99

90

8070605040

30

20

10

5

3

2

1

6.3882 5324.69 0.988 12 210.1465 4339.95 0.990 15 011.8291 4624.99 0.878 15 3

Shape Scale Corr F CTable of Statistics

SnPbAgSAC387SnAg

Variable

1.0mm Pitch, 37.5x37.5mm TBGA Varied Solder Ball AlloyIPC - 9702 Monotonic Bend Test

SAC405 SAC405


Board Assembly of Sn3.5Ag

Studied the performance of Sn3.5Ag and SAC405 at board level

• Manufacturability – robustness to reflow profile and solder paste

• Cu pad consumption

• Solder joint reliability with SnPb paste


Pure Pb-free PCB Board Mounting• Pb-free spheres: Sn3.5Ag and SAC405• Pb-free solder paste: SAC387• Pb-free reflow profile: 230~250oC peak temperature• Test vehicle: TBGA, TEPBGA• Response

• Solder sphere formation after board mounting

• Cu consumption after• 3x reflow at 240C• High temperature storage at 150oC up to 1008 hours

230,240,250

230, 240, 250

230, 240, 250

Reflow Peak Temperature

(oC)

SAC387

SAC387

SAC387

Solder Paste

37.5x37.51.27TBGA

37.5x37.51.0TBGA

27x271.0TEPBGA

Body Size(mmxmm)

Pad Pitch(mm)

Package Type


Pure Pb-free Board Mounting Process

Sn3.5Ag SAC405

230oC Peak Temperature, SAC387 solder paste, 1.0mm TEPBGA

• Sample size – 3 units per alloy per temperature• Both Sn3.5Ag and SAC405 collapsed and formed solder joint properly• No open failure was observed for both alloys in all the reflow profiles studied


Manufacturability— Board Mounting Reflow Process Evaluation at Customer

• Test Vehicle: 1.27mm TBGA with Sn3.5Ag

• Reflow profile: Pb-free board mounting with 225, 230 and 240C peak temperature

• Paste: SAC 305


Pure Pb-free Board Mounting Process— Cu consumption

Cu consumption = C - B


Pure Pb-free Board Mounting Process— Cu consumption (1.0mm Pitch TEPBGA)

• At T0 (after 1x board mounting reflow at 240C), Sn3.5Ag consumes about 3um more Cu than SAC405

• After 3x reflow at 240C reflow, Sn3.5Ag consumes 3um more Cu than SAC405

• Under high temperature storage, the Cu consumption increases with storage time for both alloys. The differences between SAC405 and Sn3.5Ag remains about the same

• The difference in Cu consumption is mainly due to the extra Cu dissolution into the Sn3.5Ag during reflow

0

2

4

6

8

10

T0 3X Reflow (240C)

Cu

Con

sum

ptio

n (u

m)

SAC405SnAg

0

2

4

6

8

10

12

T0 336hr 700hr 1008hr

Cu

Con

sum

ptio

n (u

m)

SAC405SnAg

Sample size: 14 measurements for each data point from 2 units


Backward Compatible PCB Board Mounting

•Pb-free spheres: Sn3.5Ag and SAC405•SnPb solder paste•Pb-free reflow profile: 221 and 225oC peak temperature•Test vehicle: PBGA, TEPBGA•Response

• Solder sphere formation after board mounting• Solder joint reliability

221, 225221, 225

Reflow Peak Temperature

(oC)

SnPbSnPb

Solder Paste

27x271.0PBGA27x271.0TEPBGA

Body Size(mmxmm)

Pad Pitch(mm)

Package Type


Backward Compatibility

0

20

40

60

80

100

Yiel

d (%

)

225C 221C

Sn3.5AgSAC405

0

20

40

60

80

100

Yiel

d (%

)

225C 221C

Sn3.5AgSAC405

1.0mm PBGA, SnPb Paste 1.0mm TEPBGA, SnPb Paste

• Yield loss was due to open solder joints after board mount

• SAC405 showed significant amount of open failure at 221C while Sn3.5Ag showed none

• SAC405 showed solder sphere to solder paste separation at 221C

Sample size: 13~15 units per temperature per alloy


Backward Compatible PCB Board Mounting— Solder Joint Reliability

Temperature Cycle-40~125oC

768

SAC405

SnAg

SAC405

SnAg

SAC405

SnAg

SAC405

SnAg

SAC405

SnAg

Alloy

14351x 221oC

TEPBGA

>20001x 225oC

3x 240oC27x27

Package size

(mmxmm)

1x 225oC >2000

1x 221oC

1.0

PBGA

1st Faiilure Cycles

Assembly Reflow Profile

Pad Pitch(mm)

PackageType

Sample size: 15 units per temperature per alloy


Summary

► Sn3.5Ag shows equally good manufacturability and board level solder joint reliability as SAC405

► No impact on FSL and customer manufacturing processes that have been set up for SAC405

► Sn3.5Ag has significantly better mechanical robustness at component level than SAC405 that could reduce the yield loss in package assembly and test significantly

sn3.5ag pb-free alloy for bga application€¦ · freescale semiconductor confidential and...

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