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Comparison of Pb-free Solder on UIC Test Boards and Components. Steve Dunford Nokia Mobile Phones. Agenda. UIC Pb-free Test Nokia Configurations Test Conditions X-ray Inspection First Failures Weibull Plots Intermetallic Formations in Pb-free solder Definition and examples - PowerPoint PPT Presentation
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6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Comparison of Pb-free Solder on UIC Test Boards and Components
Steve DunfordNokia Mobile Phones
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Agenda• UIC Pb-free Test Nokia
– Configurations– Test Conditions
• X-ray Inspection• First Failures• Weibull Plots• Intermetallic Formations in Pb-free solder
– Definition and examples– Reliability Improvements and Concerns– Solder Joint Voiding– Failure Mechanisms– Sn Whiskers
• Discussion• Conclusions
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Configurations Tested At Nokia
• Configuration Sn62 Sn/Ag3.8/Cu 0.7Sn/Ag3.5 Castin OSP 8 32 32 8 Ni/Au 8 32 32 8• Stencil
– .005 inch– 1/1 aperture to pad
• Reflow Profile– Peak 244°C (SnAg)– Peak 241°C (Castin, SAC)– 3 Zone Oven– Ambient Conditions
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Test Conditions
• Temp Cycle– 14 min. dwell+4 min. transition– -40°C to 125°C in single chamber– Components at temperature
• 11 minutes cold• 9.5 minutes hot
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Assembly Results• Castin
– All Solder Joints Good– Popcorned During Reflow - Improperly dried – Significant Voiding in Solder Joints – Results
Invalid– Temp Cycle Failure Data Not Used - Invalid
• SAC – 1 Open
• Polyimide tape on package• Bridged daisy chain around open
• SnAg– 1 Open
• Bridged daisy chain around open• Sn62
– All Solder Joints Good
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Assembly Results
SnAg Open SAC Open – Caused by Polyimide Tape on Component
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Early Failures – Temp Cycle 0 to 12
SAC – Ni/Au board (461) Package side failure at cycle 12
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Pb-Free Ni/Au Failures Up to 2700 Cycles
•SnAg – Ni/Au PWB, Failure on PWB at 2700 cycles Shown above.
•SAC – Ni/Au PWB, Board Side Failures 180 to 450 cycles
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
SnAg – Ni3Sn layer formed above Phosphorous rich Ni layer. Adhered well on most components
SAC Ni/Au Failures 2700 cycle
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Weibull Plots – SAC NiAu
1.00
5.00
10.00
50.00
90.00
99.00
10.00 10000.00100.00 1000.00
Generated by: ReliaSoft's Weibull++ 5.0 - www.Weibull.com - 888-886-0410
Probability Plot
Time, (t)
Unre
liability,
F(t
)
6:44:58 PM6/3/2002nokiasd
WeibullSAC-NiAu
P=2, A=RRX-R F=12 | S=0
“black pad” on PWB or Component contributed to SAC on Ni/Au failures in less than 200 cycles. Other failures not fully investigated at this time.
Solder fatigue failures
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
1.00
5.00
10.00
50.00
90.00
99.00
100.00 10000.001000.00
Generated by: ReliaSoft's Weibull++ 5.0 - www.Weibull.com - 888-886-0410
Probability Plot
Time, (t)
Unre
liability,
F(t
)
12:25:19 AM6/4/2002nokiasd
WeibullSnAg-NiAu
P=2, A=RRX-R F=13 | S=0
Weibull Plots – SnAg on NiAu
Two Failure Mechanisms – not fully investigated at this time
Solder fatigue failures
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Package Damage – 2000 cycles
Underfill separation, substrate cracks – Likely contributor to different failure mechanism. Sn62 – Ni/Au board, Failure at 2700 cycles
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Package Damage – 2700 cycles
Underfill separation, substrate cracks – Likely contributor to different failure mechanism. Sn62 – Ni/Au board, Failure at 2700 cycles
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
1.00
5.00
10.00
50.00
90.00
99.00
1000.00 10000.00
Generated by: ReliaSoft's Weibull++ 5.0 - www.Weibull.com - 888-886-0410
Probability Plot
Time, (t)
Unre
liability,
F(t
)
6:38:32 PM6/3/2002nokiasd
WeibullSAC-OSP
P=2, A=RRX-R F=10 | S=0
Sn62-NiAu
P=2, A=RRX-R F=12 | S=0
Sn62-OSP
P=2, A=RRX-R F=14 | S=0
Weibull Plots – Best Performers
SAC on OSP and Sn62 on OSP
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Intermetallic Formations in Pb-free Solder
• Necessary for durable interface between solder and solder pads
• Can Restrict Evolution of gases– Increased voiding
• Increase solder joint strength• Continue to form throughout lifetime
– Needles, dendrites, plates and tubes– Cu Pad dissolution
• Can re-direct fractures– Not Necessarily the preferred crack propagation
path• Potential for Spalling
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
X-Ray Inspection of Cycled Boards
SnAg on OSP 6500 cycles
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
X-Ray Inspection of Cycled Boards
SAC on Ni/Au 6500 cycles
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
X-Ray Inspection of Cycled Boards
CASTIN on OSP 6500 cycles
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
X-Ray Inspection of Cycled Boards
SAC on OSP 6500 cycles
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
X-Ray Inspection of Cycled Boards
SAC on OSP 6500 Cycles
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
X-Ray Inspection of Cycled Boards
SAC OSP 6500 cycles
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
X-Ray Inspection of Cycled Boards
SAC on Ni/Au 6500 cycles
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Whisker growth similar to that seen in Previous X-ray
Whisker Growth – Not Typical Sn Whisker
SnAg on OSP 6500 Cycles
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Whisker Growth - Inside Voids
SnAg Solder after 6500 cycles, -40 to 125°C
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Whisker Growth - Inside Voids
Ag/Sn forms on the end of the Sn Whisker
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Intermetallic Formations in Pb-free Solder
Sn/Ag/Cu on OSP – Intermetallic formations and Void attached to Sn/Ag intermetallic plate
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Intermetallic Formations in Pb-free Solder
Sn/Ag Plate Redirects Crack, 2700 cycles (-40 to 125°C)
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Intermetallic Formations in Pb-free Solder
Ag/Sn intermetallic redirects crack propagation, SAC/OSP (2700 cycles, -40 to 125°C)
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Intermetallic Formations in Pb-free Solder
SPALLING – Portions of Solder Joint Separating (6500 cycles, -40 to 125°C)
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Intermetallic Formations in Pb-free Solder
SPALLING – Portions of Solder Joint Separating (6500 cycles, -40 to 125°C)
Crack Propagation Arrested by Ag/Sn Flake
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Intermetallic Formations in Pb-free Solder
SPALLING – Portions of Solder Joint Separating (6500 cycles, -40 to 125°C)
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
After etch
Intermetallic Formations in Pb-free Solder
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Sink Holes
Au/Sn Intermetallics
May be associated with continued formation of intermetallic compounds
Ag/Sn Spheres
Grain Boundary
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Intermetallic Formations in Pb-free Solder
Unique Failure Mechanisms & Continued Intermetallic Growth (6500 cycles, -40 to 125°C)
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Intermetallic Formations in Pb-free Solder
SPALLING – Portions of Solder Joint Separating along grain boundaries. (SAC, 6500 cycles, -40 to 125°C)
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Intermetallic Formations in Pb-free Solder
SAC solder joints 6500 cycles and extended etch
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Intermetallic Formations SAC
SAC solder joint 6500 cycles and extended etch
SnAg3SnPlate
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Intermetallic Formations SAC
Ag3Sn spheres and dendrites form in subgrain boundaries
Sn
Ag3SnPlate
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Intermetallic Formations SAC
Fractures Form at Grain Boundaries
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Intermetallic Formations SAC
Fractures Form at Grain Boundaries
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Discussions• SAC on OSP shows equivalent or
better performance than eutectic Sn/Pb solder
– Solder Paste Print– Temperature cycling tests from –40 to 125°C
• Intermetallics in Solder Joint – Ag/Sn Plates, Spheres and dendrites in
subgrain boundaries. – Can Arrest or Redirect Cracks
• Increase Joint life– More Extensive in SAC solder
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Discussions
• Grain Boundaries Can be Preferred crack Propagation Path
– Cracks Any Location in Solder Joint• Vertical or horizontal• Potential for Spalling
• Some Concerns Remain– Increased Voiding is Likely to Occur
• Increased Intermetallic formation– Spalling Potential– Potential for Sn Whisker Growth
6/3/2002 Universal Instruments Consortium – NokiaAll Rights Reserved
Conclusions
• Pb-free processing is Viable for many applications
– Can Provide Equivalent or Better Performance over Sn/Pb solders
• Our work is not done