Design and Material Parameter Effects on BGA Solder-joint Reliability for
Automotive Applications
Burton Carpenter
Freescale Semiconductor, Inc.
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
Freescale Semiconductor Inc.
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)
Freescale Semiconductor Inc.
� 292 MAPBGA � 416 TEPBGA
Packages Investigated
Freescale Semiconductor Inc.
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
Freescale Semiconductor Inc.
� 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
Freescale Semiconductor Inc.
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
Freescale Semiconductor Inc.
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
Freescale Semiconductor Inc.
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
� Design DOE screening matrix� 16 Cells: 2��
��� fractional factorial
292MAP Experimental DOE
Freescale Semiconductor Inc.
Factor Levels
Die Thickness 0.178 mm 0.279 mm
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
Freescale Semiconductor Inc.
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
* Not statistically significant
Freescale Semiconductor Inc.
** 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
Freescale Semiconductor Inc.
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
� Design DOE screening matrix� 5 Cells: 2���
�� fractional factorial + bonus cell
416TEPBGA Experimental DOE
Freescale Semiconductor Inc.
Factor Levels
Die Thickness 0.178 mm 0.279 mm
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)
Freescale Semiconductor Inc.
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%
* Not statistically significant
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
Freescale Semiconductor Inc.
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
Freescale Semiconductor Inc.
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
22% better to first fail
- 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
42% better to first fail
41% better for 1% rate
SnAg Better
SnAg > SAC387
16% better to first fail
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.
Freescale Semiconductor Inc.
Thank You!
Freescale Semiconductor Inc.