lead free bga aatc reliability

Lead Free BGA AATC ReliabilityLead Free BGA AATC ReliabilityRound Robin Testing : UIC, Motorola and Rockwell Collins

Pb Free/June 5th 2002 2

BGA ComponentBGA Component

• 1.27mm pitch, 256 I/O daisy chain• 0.030” diameter SMD pads• 0.030” diameter spheres (variable alloy)• 0.003” encapsulant • 0.016” FR4 substrate• 0.040” glass die• 2.95 grams average weight• Electroless nickel / immersion gold finish

Encapsulant Layer

Glass Die

Solder Bumps


Test Board 6Test Board 6

• 0.062” thick FR4• Eight BGAs per board• 0.020” (2), 0.022” (4), & 0.024” (2) NSMD pads• Three surface finishes:

Electroless nickel / immersion gold (ENIG)

Copper OSP

Immersion silver (ImmAg)


Assembly - Stencil Assembly - Stencil

C1 .020" .020 x .020"C2 .022" .022 x .022"C3 .022" .022 x .022"C4 .024" .024 x .024"C5 .024" .024 x .024"C6 .022" .022 x .022"C7 .022" .022 x .022"C8 .020" .020 x .020"

PCB SitePCB Pad Diameter

Stencil Aperture

5 mil thickLaser cutStainless steel

Nominal Values

Note that square, not circular, apertures were used for this experiment.


Assembly - Pastes Assembly - Pastes

Sn/Ag (96.5,3.5); Sn/Ag/Cu (95.5/3.8/0.7);Sn/Ag/Cu/Sb (96.2/2.5/0.8/0.5) (Castin), Sn/Pb (63/37)

4 pastes with compositions identical to the solder balls were used:

All pastes were type III or type IV No Clean formulations supplied by thesame vendors as those used in the previous study.

Assembly - Bake OutAssembly - Bake OutAll BGA components were pre-baked at 125oC for a minimum of 8 hoursprior to reflow.


Lifetime & Data AnalysisLifetime & Data Analysis

Characteristic Lifetime analysis was performed with the use of Winsmith Weibull Software. Characteristic Lifetime is the numberof cycles required for 63.2% of the sample set to fail.

Lifetime was calculated for each metallurgy-pad finish combination.

PCB pad size and printed paste volume effects were not considered.

Failures not associated with in-plane solder fatigue (as determined by cross sectioning) were excluded from lifetime calculations.

Predicted lifetimes were computed using beta (slope) values from the sample set utilizing the same solder alloy and a confidence level of -95% to produce conservative estimates.

Most failures were removed from the thermal chambers following the onset of events. Event detection behavior not characterized.


UIC SnPb Reflow ProfileUIC SnPb Reflow Profile

Peak 219oCTime Above Liquidus = 44 seconds

2.67oC/sec CoolingNitrogen Atmosphere (O2 < 30 ppm)


UIC Pb-Free Reflow ProfileUIC Pb-Free Reflow Profile

Peak 241oCTime Above Liquidus = 45 seconds

2.55oC/sec CoolingNitrogen Atmosphere (O2 < 30 ppm)


UIC Temperature Cycle (Air to Air)UIC Temperature Cycle (Air to Air)

0/100C AATC104 maximum-4 minimum5 minute ramp5 minute dwell


ENIG 32/32 6801 12715Cu OSP 8/8 7335 9850

ENIG 23/28 7598 14600Cu OSP 0/8 NA >16700

ENIG 24/38 5033 15200Cu OSP 13/21 9555 16500

ENIG 7/32 8928 24700Cu OSP 2/2 9398 NA

SnAg

N63 (cycles)

SnPb

SnAgCu

SnAgCuSb

# Failures / # Samples

Solder AlloyPCB

FinishFirst Failure

(cycles)

UIC Reliability Summary*UIC Reliability Summary*

*Adjusted for non-fatigue failures.Test halted following 16700 cycles.


0/100C AATC

Lowest N63

ENIG PCB: First Failure @ 6801 Final Failure @ 16698 N63 = 12715

Cu OSP PCB: First Failure @ 7335 Final Failure @ 11066 N63 = 9850

1000 100001

2

5

10

20

3040506070809095

99

OC

CU

RR

EN

CE

CD

F %

Cycles to Failure

CMP205152

UIC SnPb Data UIC SnPb Data

CMP205112


3 3 4 44 1 1 1 1 1 1 1 14 3 4 3 1 1 1 2 2 2 1 4 4 2 2 1

3 3 3 1 1 1 1 1 1 11 1

1 11 1

1 11 1

1 1 11

11 11 21 21

2 1 4 4 4 1 1 1 1 1 62 2 2 1 1 1 1 65 5 3 3

11 1 1

111

2

1

1 1 1 1

Failure Frequency SnPb on ENIG 27 Components

Failure Frequency SnPb on Cu OSP

8 Components

UIC SnPb Data UIC SnPb Data


CMP205152: First UIC SnPb Failure CMP205152: First UIC SnPb Failure

0/100C AATCFailure @ 6801Removed After Cycle 68026 Events Detected4.42 Ohm Initial Resistance4.78 Ohm Final ResistanceENIG PCBOuter Corner of PackageComponent Side Solder Fatigue

SnPb Solder Fatigue


CMP205112: Final UIC SnPb Failure CMP205112: Final UIC SnPb Failure

0/100C AATCFailure @ 16698Removed After Cycle 167002 Events Detected5.80 Ohm Initial Resistance6.38 Ohm Final ResistanceENIG PCBNo Joint Isolated by 4 PointCleaving in Outer Row

Potential Cleaving of SnPb Solder Joint


UIC SnAgCu Data UIC SnAgCu Data

1000 100001

2

5

10

20

30405060708090

OC

CU

RR

EN

CE

CD

F %

Cycles to Failure

CMP205045 (Excluded from Lifetime Analysis:

Interfacial Failure)

0/100C AATC

ENIG PCB: First Failure @ 2465 Second Failure @ 7598 N63 = 14600

*No Failures on Cu OSPThrough 16700 Cycles*20300 N63 Prediction

CMP205048

\WB c=-95

Cu OSPPredicted


UIC SnAgCu Data UIC SnAgCu Data

1 1 1 1 1 1 2 2 31 1 1 2

2 1 11 2 1

2 213 12 13 12

1 1 41 1 2211 1 1 1

1 2 1 2 2 2

1 1

Failure Frequency SnAgCu on ENIG 21 Components


CMP205045: First UIC SnAgCu Failure CMP205045: First UIC SnAgCu Failure

0/100C AATCFailure @ 24655.1 Ohm Initial ResistanceElectrically Open at RemovalENIG PCBOuter Corner of PackageNon-Solder Fatigue Failure

Interfacial Failure

Enlarged Image


CMP205048: First UIC SnAgCu Fatigue Failure CMP205048: First UIC SnAgCu Fatigue Failure

0/100C AATCFailure @ 7598Removed After Cycle 76335.10 Ohm Initial Resistance5.20 Ohm at RemovalENIG PCBOuter Corner of PackageComponent Side Solder Fatigue

SnAgCu Solder Fatigue


CMP205057 SnAgCu on ENIG 11938 CTF

PCB Side Fatigue Failure5.21 Ohm Initial Resistance5.99 Ohm Final Resistance

CMP205052 SnAgCu on ENIG 10880 CTF

Component Side Fatigue Failure5.17 Ohm Initial Resistance20.0 Ohm Final Resistance

UIC SnAgCu Failure Modes UIC SnAgCu Failure Modes


CMP205036 SnAgCu on ENIG14115 CTF

Electrically Good JointCracks Visible in X-ray

UIC SnAgCu Failure Modes UIC SnAgCu Failure Modes

CMP205034 SnAgCu on ENIG 16700 Cycles to Removal

Electrically Good, Non-Failure


UIC SnAgCuSb Data UIC SnAgCuSb Data

Glass Delamination (Excluded)

Interfacial Failure(Excluded)

Large Void(s)(Included)

1

2

5

10

20

30405060708090

OC

CU

RR

EN

CE

CD

F %

1000 10000Cycles to Failure

Excluded

0/100C AATC

ENIG PCB: N63 = 15200

Cu OSP PCB: N63 = 16500


UIC SnAgCuSb Data UIC SnAgCuSb Data 1 1

1 11 1 1

11 1

11

1 1 1 2 1 1 11 1

1 1 4 4

Failure Frequency SnAgCuSb on ENIG

19 Components1 1 1

1 1 1 1 1

11 21 2

2

111

1 1 1

Failure Frequency SnAgCuSb on Cu OSP

10 Components


Delamination is the separation of theunderfill material from the substrate and/or the glass die.

Primarily occurs during reflow operations.

Delamination affects both in-plane andout-of-plane stresses.

Some degree of delamination located near the center of the package is acceptable.

Delamination may be visible to the naked eye or may require C-SAM to identify.

Effects of Delamination Effects of Delamination

CMP205126 SnAgCuSb on Cu OSP 2137 CTF

Visible Delamination

Effect of Delamination


Effects of Delamination : Warpage Effects of Delamination : Warpage

CMP205126 SnAgCuSb on Cu OSP PCB

Room Temperature

100 Degrees Celsius


CMP205013 SnAgCuSb on ENIG6105 CTF

Solder Fatigue through Large Voids 5.39 Ohm Initial Resistance5.70 Ohm Final Resistance

CMP205132 SnAgCuSb on Cu OSP3990 CTF

Interfacial Failure4.51 Ohm Initial Resistance4.62 Ohm Final Resistance

UIC SnAgCuSb Failure Modes UIC SnAgCuSb Failure Modes


CMP205919 SnAgCuSb on ENIG16700 Cycles to Removal

Electrically Good, Non-FailureCleaving Observed in Outer Row


Typical FailureCracks on Component and PCB Side

Numerous Voids Present5.93 Ohm Initial Resistance6.02 Ohm Final Resistance

UIC SnAgCuSb Failure Modes UIC SnAgCuSb Failure Modes


UIC SnAg Data UIC SnAg Data

1

2

5

10

20

30405060708090

OC

CU

RR

EN

CE

CD

F %


0/100C AATC

Highest N63

ENIG PCB: First Failure @ 8928 7th Failure @ 15896 24702 N63 Prediction

Cu OSP PCB: First Failure @ 1534 Final Failure @ 10204 6/8 Defective No Prediction Provided


UIC SnAg Data UIC SnAg Data 2 2 1 1

1 1 1

1 1 2 2

1 1

1 1 1 1

Failure Frequency SnAg on ENIG 7 Components

Failure Frequency SnAg on Cu OSP

2 Components



CMP205074 SnAg on Cu OSP1534 CTF

Glass Delamination

CMP205069 SnAg on Cu OSP 4575 CTF

Interfacial Failure Electrically Open Upon Failure


CMP205070 SnAg on Cu OSP10204 CTF

PCB Side Solder Fatigue5.10 Ohm Initial Resistance40.56 Ohm Final Resistance


Thick Cu-Sn Intermetallics

Cu

Non-reflow Voids


Motorola SnPb Reflow ProfileMotorola SnPb Reflow Profile

Peak 221oC1.3oC/sec CoolingTAL = ~115 secondsNitrogen Atmosphere


Motorola Pb-Free Reflow ProfileMotorola Pb-Free Reflow Profile

Peak 242oC1.2oC/sec CoolingTAL = 46 secondsNitrogen Atmosphere


Motorola Temperature Cycle (Air to Air)Motorola Temperature Cycle (Air to Air)

0/100C AATC107 maximum-7 minimum10 minute ramp5 minute dwell


ENIG 14/14 5885 8495Cu OSP 8/8 7631 8730

ENIG 14/16 7356 10290Cu OSP 7/8 8051 10870

ENIG 7/8 7713 9295Cu OSP 1/8 11261 >13707

ENIG 4/16 7812 15318Cu OSP 1/8 13521 >13707

Solder AlloyPCB

Finish

SnPb

SnAgCu

SnAgCuSb

SnAg


First Failure (cycles)

N63 (cycles)

Motorola Reliability Summary*Motorola Reliability Summary*

*Adjusted for non-fatigue failures.Based on data accumulated through 13707 cycles.


10001

2

5

10

20

304050607080909599

OC

CU

RR

EN

CE

CD

F %

10000Cycles to Failure

Motorola SnPb Data Motorola SnPb Data

0/100C AATC

Lowest N63

ENIG PCB: First Failure @ 2959 Final Failure @ 9914 N63 = 8495 Cu OSP PCB: First Failure @ 7631 Final Failure @ 9179 N63 = 8730

Excluded(Interfacial Failures)

CMP205656


Motorola SnPb Data Motorola SnPb Data 1 11 1 1 1 1 1 1 1 1

1 1 1 1 1 11 1 2 2 2 1 1 11 1 1

11

111

1 1 1 21 1 1 21 1 1

1 1 1 1 1 21 3 3 2 1 1 2 1 1 2

3 3 2 2 1 1 1 2 2 2 3 3 31 1 1 1 1 11 11

1 21 11 1

11 11 1 1 1

1 1 11 1 11 1

1 1 1 1 1 1 11 1 1 1 1 1

Failure Frequency SnPb on Cu OSP

4 Components

Failure Frequency SnPb on ENIG 7 Components


CMP205225 SnPb on ENIG2959 CTF

Interfacial Failure


Interfacial Failure

Motorola SnPb Failure Modes Motorola SnPb Failure Modes


Motorola SnPb Failure Modes Motorola SnPb Failure Modes


First Solder Fatigue Failure


Motorola SnAgCu Data Motorola SnAgCu Data

1

2

5

10

20

30405060708090

OC

CU

RR

EN

CE

CD

F %


0/100C AATC

ENIG PCB: First Failure @ 7356 14th Failure @ 11188 N63 = 10290 Cu OSP PCB: First Failure @ 8051 7th Failure @ 12200 N63 = 10870

CMP205563CMP205625


1 1 11 1 1

1

1

1 1 11

Failure Frequency SnAgCu on ENIG 7 Components

Motorola SnAgCu Data Motorola SnAgCu Data


Motorola SnAgCu Failure Modes Motorola SnAgCu Failure Modes

CMP205563 SnAgCu on ENIG7356 CTF

First SnAgCu Solder Fatigue Failure


CMP205625 First SnAgCu on Cu OSP PCB Failure

8051 CTF

Motorola SnAgCu Failure Modes Motorola SnAgCu Failure Modes

Silver Needle

Copper

Non-reflow Voids


Motorola SnAgCuSb Data Motorola SnAgCuSb Data

1

2

5

10

20

30405060708090

OC

CU

RR

EN

CE

CD

F %


0/100C AATC

ENIG PCB: First Failure @ 7713 7th Failure @ 11062 N63 = 9295

Cu OSP PCB: First Failure @ 11261 14245 N63 Prediction

Cu OSPPredicted

\WB c=-95

CMP205455


Motorola SnAgCuSb Failure ModesMotorola SnAgCuSb Failure Modes


First SnAgCuSb Solder Fatigue Failure

Cleaving?


Motorola SnAg Data Motorola SnAg Data

1

2

5

10

20

30405060708090

OC

CU

RR

EN

CE

CD

F %


\WB c=-95

0/100C AATC

ENIG PCB: First Failure @ 6945 4th Failure @ 12858 15318 N63 Prediction Cu OSP PCB: First Failure @ 13521 16000 N63 Prediction

ENIGPredicted

\WB c=-95

Cu OSPPredicted

CMP205426


Motorola SnAg Data Motorola SnAg Data

1 111

11

1 1

Failure Frequency SnAg on ENIG 4 Components


Motorola SnAg Failure Modes Motorola SnAg Failure Modes

CMP205426 SnAg on ENIG6945 CTF

First SnAg Solder Fatigue Failure


Rockwell Data Rockwell Data

-55 to 125oC Air to Air Thermal Cycle

All Components were Assembled to Immersion Silver PCBs

All Components were Assembled with SnAgCu (95.5/3.8/0.7) Solder Paste:

Sphere Alloy Sn Pb Ag Cu

3.800 0.700

96.432 0.000 3.519 0.04996.5Sn3.5Ag

95.5Sn3.8Ag.7Cu 95.500 0.000

Alloy Composition % on .022" Pad

63Sn37Pb 0.0490.26334.41965.270

Estimated alloy % based on 90% paste transfer and 50% solidified paste volume.


Rockwell Reliability Summary* Rockwell Reliability Summary*

9/31 467 2667

16/32 413 1990

13/32 367 2860

ImmAg

ImmAg

ImmAg

Solder AlloyPCB

Finish

SnPb

SnAgCu

SnAg


First Failure (cycles)

N63 (cycles)

*Adjusted for non-fatigue failures.Based on data accumulated through 2000 cycles.

ENIG components


Rockwell Reliability Data Rockwell Reliability Data

1

2

5

10

20

30405060708090

OC

CU

RR

EN

CE

CD

F %


-55/125C AATC

ImmAg PCB:

SnPb N63 = 1990

SnAg N63 = 2667

SnAgCu N63 = 2860

ENIG Components on ImmAg PCBs

CMP205205Excluded


CMP205163 SnPb on ImmAg413 CTF

Bulk Solder Failure


Bulk Solder Failure

Rockwell SnPb Failure Modes Rockwell SnPb Failure Modes


Bulk Solder Failure

Copper

Nickel

Tin

Lead

Copper

Tin

Silver

Lead


Rockwell SnAg Failure Modes Rockwell SnAg Failure Modes

Copper

Nickel

Tin

Silver

CMP205205 SnAg on ImmAg184 CTF

Interfacial Failure



Bulk Solder Failure


Bulk Solder Failure




CMP205192 SnAg on ImmAg 1528 CTF

Bulk Solder Failure

Non-reflow Voids

Cu-Sn


CMP205277 SnAgCu on ImmAg367 CTF

Intermetallic (Cu-Sn) to Bulk Solder Failure

Rockwell SnAgCu Failure Modes Rockwell SnAgCu Failure Modes

Copper

Tin

Silver




Intermetallic (Cu-Sn) to Bulk Solder Failure

Cu-Sn


CMP205740 SnAgCu on ImmAgCu Component

1530 CTF


Silver Needle


UIC and Motorola SnPb:

Solder joints consistently fractured through the bulk solder material near the mask defined component attachment pad.

A few interfacial failures occurred at the component electroless nickel / solder interface.

Minor cleaving was observed on one sample following 16700 AATCs. Cleaving did not lead to failure.

Lowest characteristic life among alloys tested.

ConclusionsConclusions

*Results may be highly influenced by such factors as the reflow profile and test cycle conditions.*



UIC and Motorola Lead Free:

All alloys demonstrated superior fatigue resistance compared to SnPb. SnAg most reliable.

Bulk solder fatigue occurred near the component attachment pad and PCB attachment pad. No relation between PCB pad size and crack location was evident.

Fatigue cracks are often very fine, with multiple crack fronts influenced by the local microstructure of the solder. A completely cracked joint can be electrically continuous. May explain “glitch”.



UIC and Motorola Lead Free:

Several interfacial failures were observed at electroless nickel / solder interfaces.

Severe cleaving was observed on electrically good samples. Cleaving may occur before in-plane crack propagation and potentially lead to solder bridging.

The CASTIN alloy contained large voids which resulted in early failures. These early failures may occur before SnPb failures.

Data indicates higher reliability on copper OSP PCBs. Thick intermetallics, often greater than .25 mil may form at the copper / solder interface.

5 lead free components on ENIG with atypical event pattern. Evidence of “glitch”?


ConclusionsConclusionsRockwell SnPb with SnAgCu paste:

Solder joints consistently fractured through the bulk solder material near the component or PCB attachment pad.

Lowest characteristic life among alloys tested.

Rockwell Lead Free:

Both alloys demonstrated superior fatigue resistance compared to SnPb. Prediction: SnAgCu most reliable. SnAg reliability is comparable.

Two failure mechanisms observed: 1.) Fracture through the bulk solder material near the component or PCB attachment pad. Similar to fine cracks observed in other tests.2.) Failure between the solder material and Cu-Sn IMC near the PCB pad. Unique among the other tests.

Non-reflow voiding prevalent at failure location.


Continuing Work Continuing Work

Picture by Amkor Technology

Alloy PCB # SamplesENIG 32OSP 32ENIG 32OSP 32

SnPb

SnAgCu

Partial repeat of experiment with commercially available components:

Completed 1256 0 to 100oC cycles without failure.

• 1.27mm pitch, 256 I/O daisy chain• 0.0177” diameter SMD pads• 0.030” diameter spheres (variable alloy)• SnPb Reliability: N63 = 7700 - 8200 Cycles


Continuing Work Continuing Work

Encapsulant Layer

Glass Die

Solder Bumps

Partial repeat of first experiment with NSMD components:

Alloy PCB # SamplesENIG 32OSP 24ENIG 32OSP 24ENIG 32OSP 24

SnPb

SnAgCu

SnAg

AATC Test Matrix

lead free bga aatc reliability

Documents

enig4 components motorola

final failure

enig19 components uic

outall bga components

lifetime calculations

cu osp pcb

nonfatigue failures

numberof cycles