Design and Material Parameter Effects on BGA Solder-joint ... · Typical solder-joints at 3000...

Design and Material Parameter Effects on BGA Solder-joint Reliability for

Automotive Applications

Burton Carpenter

Freescale Semiconductor, Inc.

[email protected]

Authors:Burton Carpenter, Thomas Koschmieder*,

Brett Wilkerson, Torsten Hauck Ph.D., John Arthur

* Now at Cirrus Logic

Outline/Agenda

� Introduction

� Simulations

� Results of Experiments

� 292MAPBGA

� 416TEPBGA

� Summary

� Conclusions

� Q & A

Freescale Semiconductor Inc.

Introduction

� Background� Solder-joint lifetime testing -40°C to +125°C

� Automotive requiring 2000+, 3000+ cycles

� Improved reliability, elimination of underfill

� Purpose of the study� Packages:

� 292MAPBGA:17mm x 17mm, 0.8mm pitch

� 416TEPBGA: 27mm x 27mm, 1.0mm pitch

� Understand effects of BOM & Design parameters

� Quantify improvements


Approach

Review Existing DataDetermine if criteria can be met

Simulations

FEM Construction and Validation

292MAP Simulation:Determine significant parameters

(screening DOE, 8 variables)

Experiments292MAP Experiment DOE:Validate FEM (Screening DOE, 6 variables)

Quantify SJR

292MAP Confirmation Experiment:Larger sample verification of DOE

(1 variable)

416TEPBGA Experiment DOE:Effect of parameters

Quantify SJR (3 variables)


� 292 MAPBGA � 416 TEPBGA

Packages Investigated


Parameter 292MAP 416PBGA

Body Size 17mm x 17mm 27mm x 27mm

Mold Size 17mm x 17mm 24mm x 24mm

Mold Cap 0.8mm 1.15mm

BGA Pitch 0.8mm 1.0mm

Die Size7.0mm (DOE)

9.2mm (confirm)8.6mm x 9.3mm

Layer Count 4

Pad Finish Electroplated Ni/Au

MoldCompound

PCB

Package Substrate

MoldCompound

PCB

Package Substrate

No MCMC to edge

Die

Outline

DOE Die Outline

Confirm Die Outline

� Component FEM Model

� Correlation of

component model with

warpage data

� Solder interconnect

shape predicted

� Complete FEM model

FEM ConstructionMold CompoundPackage Substrate Chip Die Attach

PCB

ComponentSolder Joint

Solder shape predicted assuming truncated sphere

0.5mmSolder Ball

0.4mm SRO & PCB pad

0.5mmSolder Ball

0.5mm SRO & PCB pad

Component model compared to historical warpage (Thermoire) data for 208MAP package


� Simulate temperature cycle -40°C to +125°C for test case

� Non-linear creep deformation predicted as a measure of material fatigue.

� Comparison of high creep strain solder-joints with experimentally observed failing joints

FEM Validation

Component Side

PCB Side

Example creep solder jointRed = High Creep StrainBlue = Low Creep Strain

125°C

-40°C0%

1%

2%

0 30 60 90 120 150 180

Acc

um

ula

ted

Cre

ep

Str

ain

Time (min)

Temp


Higher creep strain

Red indicatingsolder cracks

Simulated creep strain Failure pattern on 208MAP

292MAP Simulation DOE

� Identify potentially significant parameters & levels

� Parameters held constant:� PCB: 1.6mm 4-layer� PCB pad: NSMD matching package pad diameter� Solder Alloy: SAC405

� Design DOE screening matrix� 20 Cells: 2��

�� fractional factorial plus 4 center points


Factor Levels

Mold Compound CTE 8 ppm/°C 12 ppm/°C

Mold Cap Thickness 0.700 mm 0.800 mm

Die Thickness 0.178 mm 0.356 mm

Substrate Thickness 0.380 mm 0.560 mm

Substrate Core CTE 11 ppm/°C 17 ppm/°C

Package Pad Type SMD NSMD

Package Pad Diameter* 0.400 mm 0.500 mm

Sphere Diameter 0.400 mm 0.500 mm

* Package Pad Diameter =

Metal pad for NSMD

SRO (Solder Resist Opening) for SMD

292MAP Simulation Results� Simulate temperature cycle -40°C to +125°C for each “cell”� Extraction of 2 parameters:

� Maximum creep strain (crack initiation)� Average creep strain (crack propagation)

� DOE analysis:� Regression of creep strain vs. independent variables� Identify significant variables

Factor Change Max creep strain Avg creep strain

Mold Compound CTE 8 �10 ppm/°C * *

Mold Cap Thickness 0.7mm � 0.8mm * *

Die Thickness 14mil � 7 mil 44% 50%

Substrate Thickness 0.38mm � 0.56mm * *

Substrate Core CTE 11 �17 ppm/°C * *

Package Pad Type SMD � NSMD 32% *

Package Pad Diameter 0.4mm � 0.5mm 40% 36%

Sphere Diameter 0.4mm � 0.5mm * *

* Not statistically significant


Lower creep strain = longer solder-joint life

MoldCompound

PCB

Package Substrate

� Identify potentially significant parameters & levels

� Parameters held constant:� Package 17x17mm, 0.8mm BGA pitch, die 7.0x7.0mm� PCB: 1.5mm 4-layer� PCB NSMD pad: , diameter matching SRO


�� fractional factorial

292MAP Experimental DOE


Factor Levels


Substrate Thickness 0.380 mm 0.560 mm

Package Pad Type SMD NSMD

Package Pad Diameter 0.400 mm 0.500 mm

Sphere Diameter 0.400 mm 0.500 mm

Solder Alloy SAC305 SnAg

Significant from Simulation DOE


292MAP DOE – Crack Growth� Method:

� Dye-and-pry

� One part per cell at 3000, 4000, 5000 cycles

� Largest cracked area on each sample – averaged for all 8 cells for each pad type

� Result� NSMD had significantly less cracking – as predicted by FEM

� But NSMD failures occurred sooner – different failure mode: package substrate trace crack

0%

20%

40%

60%

80%

100%

2500 3000 3500 4000 4500 5000

Cra

cke

d S

old

er

Join

t A

rea

-M

ax

(%

)

Cycles -40/125C

Crack Growth vs. Package Pad Type

NSMD SMD

Package substrate trace crack

NSMDaverage first electrical failure ~3000

SMD average first electrical failures ~3740

292MAP DOE Regression

� SMD data only� Purpose to study solder-joint life due to cracking

� Analyzed as 8 Cells: 2�� fractional factorial

� 2nd order effects confounded with first order

� Results used as guide for next experiments

Factor Change First Failure

Die Thickness 11mil � 7mil 22%

Substrate Thickness 0.38mm � 0.56mm *

Package Pad Type SMD � NSMD Changed fail mode, not in model

Package Pad Diameter** 0.4mm � 0.5mm 32%

Sphere Diameter 0.4mm � 0.5mm Interaction with Pad Diameter

Solder Alloy SAC305 � SnAg Interaction with Pad Diameter



** Package Pad Diameter =

Metal pad for NSMD

SRO (Solder Resist Opening) for SMD

292MAP Confirmation Experiment� Compare 0.4mm and 0.5mm SRO� Independently monitor corner solder-joints� 0.5mm SRO 2x better (1% fail rate)� 0.4mm SRO corner joints have much higher failure rate� Corners different fail mode: diagonal cracks, PCB cracks


58%

34%

Package

PCB

41%

0%

Package

PCB

60%

20%

Package

PCB

61%

0%

Package

PCB

Corner Other

0.4mmSRO

0.5mmSRO

Typical solder-joints at 3000 cycles

0.4mm

Corner

Joints

0.5mm

Corner

Joints

0.5mm

Other

Joints

Number of AATS (-40/125C)

% P

acka

ge

s F

aile

d

1

2

5

10

30

50

70

90

3000 40001000 2000 5000

0.4mm

Other

Joints

Corner Balls Other

Each package has two nets

MoldCompound

PCB

Package Substrate

No MC

� Establish performance of larger package

� Parameters held constant:� Package 27x27mm, 1.0mm BGA pitch, die 8.6x9.3mm� PCB: 1.5mm 4-layer� PCB 0.45mm NSMD pad


�� fractional factorial + bonus cell

416TEPBGA Experimental DOE


Factor Levels


Substrate Thickness 0.560 mm

Package Pad Type SMD

Package Pad Diameter* 0.500 mm 0.600 mm

Sphere Diameter Match SRO

Solder Alloy SAC387 SnAg

Significant from 292MAP Experiment

* Package Pad Diameter =SRO

416PBGA Regression� SRO effect similar to 292MAP

� Die thickness not a factor:

� Larger package failing on outer rows

� SnAg better than SAC

� 50% improvement (cell 3 vs. 2)


Factor Change First Failure 1% Fail Rate

Die Thickness 11mil � 7mil * *

SRO/Solder Ball 0.5mm � 0.6mm 42% 41%

Solder Alloy SAC387 � SnAg 16% 11%


3000 5000

Number of AATS (-40/125C)

% P

acka

ge

s F

aile

d

1000 100001

10

30

50

70

90

99

Cell 2:0.5mm SRO,

SAC387,

11mil die

Cell 3:0.6mm SRO,

SnAg,

11mil die

Cell 5:0.6mm SRO,

SnAg,

7mil die

416PBGA Cross-section Results

� Examine 3 rows

of solder-joints

� Smaller SRO

failing on

package side

� Larger SRO

distributes strain

more evenly

between package

and PCB


Spheres with ≥ 50% Cracking @ 4000 cycles

Cell 2:0.5mm SRO, SAC387, 11mil die

Cell 3:0.6mm SRO, SnAg, 11mil die

Package

PCB

A21

25%

66%

D07Package

PCB

100%

21%

A

D

K

Die Outline

A

D

K

Die Outline

Both SidesPackage SidePCB Side

Summary


Package SRO + Solder Ball Solder Alloy Die ThicknessSolder-Joints

Prone to Fail

Crack Location in

Solder-Joint

292MAP

Simulations

Larger SRO Better:

0.5mm > 0.4mm

14% better

Not Studied Thinner Die Better

7mil > 14mil

56% better

- Package corners

- Die perimeter

- Package side

292MAP

DOE Exp.

Larger SRO Better:

0.5mm > 0.4mm

32% better to first fail

Interaction with SRO

0.4mm SRO: SnAg >

SAC305

0.5mm SRO: SAC305

> SnAg

Thinner Die Better

7mil > 11mil


- Die perimeter

- Package corners

on 0.4mm SRO

- Primarily package

side for SMD

292MAP

Confirm

Exp.

Larger SRO Better:

0.5mm > 0.4mm

33% better to 1%

failure rate (excluding

corner balls)

Not Studied Not Studied - Die perimeter

- Package corners

on 0.4mm SRO

- Primarily package

side

- Corner joint show

PCB side and diagonal

cracks

416PBGA

DOE Exp.

Larger SRO Better:

0.6mm > 0.5mm


41% better for 1% rate

SnAg Better

SnAg > SAC387


11% better for 1% rate

Not Significant - Corners and

outer perimeter

rows

- Primarily package

side for 0.5mm SRO

- Package and PCB

side for 0.6mm SRO

Clear

Signal

Mixed

Signal

Depends

on package

type

Depends

on package

details

Package

side when

ratio ~1:1

Conclusions� Modeling reduces overall effort

� Reduce number of variables for empirical evaluations� Estimate solder-joint reliability of similar but new package types

� Meeting stricter automotive requirements� Packages now available or with minor improvements

� Strong influence of package SRO� 32%-42% improvement by increasing 100µm over the “50% rule”

� SnAg solderball� Improves solder-joint life over SAC alloys in most instances

� Die Thickness� Thinner die improve joint-life for packages prone to fail at die edge

� Corner solder-joints� Diagonal (rather than horizontal) cracks� Failure rates that change depending on SRO.


Thank You!


Design and Material Parameter Effects on BGA Solder-joint ... · Typical solder-joints at 3000...

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