reliability of electrical interconnectsprincipal investigator national renewable energy laboratory...
TRANSCRIPT
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.
Douglas DeVoto Principal Investigator National Renewable Energy Laboratory Annual Merit Review and Peer Evaluation Meeting June 18, 2014 Washington, D.C. PR-5400-61358
This presentation does not contain any proprietary, confidential, or otherwise restricted information.
Reliability of Electrical Interconnects
Project ID: APE036
2
Overview
Timeline • Project Start Date: FY11 • Project End Date: FY14 • Percent Complete: 80%
Barriers and Targets • Efficiency • Performance and Lifetime
Budget • Total Project Funding:
DOE Share: $1,600K
• Funding Received in FY13: $450K
• Funding for FY14: $300K
Partners • Interactions/Collaborations
o Curamik, Kulicke and Soffa
• Project Lead o National Renewable Energy
Laboratory
3
Relevance
Ribbon Bonding
400 µm
2,000 µm x 200 µm
400 µm
400 µm
Three 400-µm wires can be replaced by a single 2,000-µm x 200-µm ribbon for equivalent current carrying capability.
Traditional Power Electronics Package
Wire Bonding
IGBT/Diode Die
Metalized Substrate Substrate Attach
Base Plate
Die Attach
Interconnect Encapsulant
Enclosure Terminal
4
Relevance
• Technology Benefits o A transition from round wire interconnects to ribbon interconnects
allows for higher current densities, lower inductances, and lower loop heights.
• Overall Objective
o Identify failure modes in ribbon bonds, experimentally characterize their life under known conditions, and develop and validate physics-of-failure (PoF) models that predict life under use conditions.
o Test and model ribbon bonds to prove they exhibit equivalent or greater reliability than industry-accepted wire bond technology.
• Uniqueness and Impacts
o Failure modes and PoF models for emerging interconnect technology.
5
Milestones 2013 2014
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Fabricate samples at Kulicke and Soffa for 51 additional test substrates.
Measure baseline ribbon bond strength.
Conduct accelerated life testing plan.
Validate lifetime estimation models for specific failure modes observed in accelerated tests.
Go/ No-Go
Key Deliverable
Go/No-Go: Ribbon bonds must meet minimum pull strength before proceeding with accelerated tests.
Key Deliverable: Report on the reliability of ribbon bond technology to industry.
6
Overview Sample Synthesis
Ribbon Bonding
Accelerated Testing Temperature
Elevation Temperature
Cycling
Power Cycling
Corrosion Testing
Vibration Testing
Pull Testing
Sample Evaluation
Lifetime Estimation
Model Validation
Approach
Bond Pad Optimization
7
Sample Synthesis
Criterion Variation
Bonding Material Al Ribbon
Cu/Al-Clad
Ribbon Al Wire
Cross Section (µm) 2,000 x
200 Ribbon
1,000 x 100
Ribbon
300⌀ Wire
Ribbon Span (mm) 10 20
Tool Pattern Waffle Three-Ridge
Ribbon Stacking Not Stacked Stacked
Forced Bond Angle (°) 0 20
Bonding Power Level Low High
Bond Pad Interface Cu Si (Al)
Ribbon Material
Ribbon Span
Ribbon Cross Section
Tool Pattern
Forced Bond Angle Stacked Pads
Approach
8
Accelerated Testing Plan Accelerated Test Testing Condition Duration Standard
Initial Pull Test - - -
Temperature Elevation 150°C 500/1,000 hours JESD22-A103D
Temperature Cycling -40°C to 150°C, less than 20 second transition time 1,500/3,000 cycles JESD22-A104D
Corrosion Testing
130°C, 85% relative humidity 96 hours JESD22-A110D
110°C, 85% relative humidity 264 hours JESD22-A110D
121°C, 100% relative humidity 96 hours JESD22-102D
Power Cycling 40°C to 120°C, ~ 2 second cycled DC bias 3,000 cycles JESD22-A105C
Vibration Testing Combined vibration and thermal cycling Until interconnect fails HALT
Approach
Temperature
Vibration
Temperature + Vibration
Shear Stress
Flexural Stress Corrosion
Intermetallics
CTE (x 10-6/K) Silicon: 2.6 Copper: 16.5 Aluminum: 22.7
20
40
60
80
100
0 2 4 6 8
Tem
pera
ture
(°C)
Time (s)
Power CyclingThermal Cycling
9
Sample Evaluation
1
2 3
4 5
Failure Modes 1: Wire/ribbon break 2: Heel failure – substrate 3: Heel failure – die 4: Bond lift-off – substrate 5: Bond lift-off – die
• Ribbon pull testing indicates the strength of the ribbon bond. • Bond strength and failure mode is recorded for each bond.
Approach
10
Sample Evaluation
Failure Mode: Wire Break
Approach
11
Sample Evaluation
Failure Mode: Heel Failure from Substrate
Approach
12
Sample Evaluation
Failure Mode: Bond Pad Lift-off from Substrate
Approach
13
Sample Evaluation • The minimum bond strength is specified by MIL-STD-883H Method
2011.8. o Minimum bond strength requirement increases with respect to
increasing interconnect cross-sectional area.
1,000 x 100 µm, 1.28 N 500 µm, 2.13 N 2,000 x 200 µm, 3.50 N
300 µm, 0.96 N
0.01
0.1
1
10
10 100 1,000
Min
imum
Bon
d Pu
ll Li
mit
(N)
Equivalent Wire Diameter (µm)
Minimum Bond Strength
Approach
14
Sample Test Substrates • 51 test boards bonded at Kulicke and Soffa.
o 48 ribbons bonded per board in 12 parallel electrical paths. o Loop height to span ratio is 1:2.2.
Ribbon Bonding Test Board Layout
10 mm span, 0° angle, 8x
20 mm span, 0° angle, 7x 20 mm span, 20° angle, stacked, 3x
20 mm span, 20° angle, 6x
Low Power Level High Power Level
Technical Accomplishments
15
Bond Optimization
10
14
18
22
26
1,000 1,200 1,400 1,600 1,800
Defo
rmat
ion
(μm
)
Current (mA)
Current (mA)
Deformation (µm)
Deformation (visual)
1,070 11
1,210 15
1,370 19
1,490 21
1,630 23
• Ultrasonic bonding power, force, and application time contribute to the quality of the bond pad.
• Bond quality is measured by: o Bond pad deformation o Pull strength o Failure mode.
• Deformation pattern depth increases with increasing current levels.
Technical Accomplishments
16
Bond Optimization • Pull strength of test bonds was
measured to be approximately 9.8 N. • Pull failure modes varied with bond
current levels. o These criteria were used for
final selection of optimized bonding current level.
1
2 3
4 5
Failure Modes 1: Wire/ribbon break 2: Heel failure – substrate 3: Heel failure – die 4: Bond lift-off – substrate 5: Bond lift-off – die
0%
25%
50%
75%
100%
1,070 1,210 1,370 1,490 1,630
Failu
re M
ode
Perc
enta
ge
Bonding Current Level (mA)
1: Wire/ribbon break
2: Heel failure – substrate
3: Heel failure – die
4: Bond lift-off – substrate
5: Bond lift-off – die
Technical Accomplishments
17
Baseline Evaluation • Initial pull testing was completed on test substrates prior to accelerated
testing: o Al wire has a cross-section of 500 µm. o Ribbon interconnects have 1,000 µm x 100 µm cross-sections. o Bonding power for ribbon interconnects is specified as either low or
high.
Technical Accomplishments
0
5
10
15
20
25
30
Pull
Forc
e (N
)
Interconnect Material
10 mm20 mm
Al Wire Cu/Al Ribbon (low) Cu/Al Ribbon (high) Al Ribbon (high) Al Ribbon (low)
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0%
25%
50%
75%
100%
Al Wire Cu/Al Ribbon (low) Cu/Al Ribbon (high) Al Ribbon (low) Al Ribbon (high)
Failu
re M
ode
Perc
enta
ge
Bonding Method
Wire/ribbon break
Heel failure
Bond lift-off
Baseline Evaluation • The failure mode was recorded for each
bond prior to accelerated testing: o Al wire bonds and Cu/Al-clad
ribbon failures showed bond lift-off failures.
o Al ribbon bonds exhibited heel failures.
1
2 2
3 3
Failure Modes 1: Wire/ribbon break 2: Heel failure 3: Bond lift-off
Technical Accomplishments
19
Accelerated Test Testing Condition Duration Temperature Elevation 150°C 500/1,000 hours
Post-Accelerated Testing Evaluation Technical Accomplishments
6789
101112
Pull
Forc
e (N
)
Testing Time
Al Ribbon (low) Temperature Elevation 10 mm20 mm
Initial 500 hours 1,000 hours
4
5
6
7
8
9
10
Pull
Forc
e (N
)
Testing Time
Al Ribbon (high) Temperature Elevation 10 mm20 mm
Initial 500 hours 1,000 hours
20
Temperature Elevation Evaluation • The failure mode was recorded for each
bond after temperature elevation testing: o Al ribbon heel failure mode
remained the same through temperature elevation testing.
1
2 2
3 3
Failure Modes 1: Wire/ribbon break 2: Heel failure 3: Bond lift off
Technical Accomplishments
0%
25%
50%
75%
100%
Initial 500 hours 1,000 hours
Failu
re M
ode
Perc
enta
ge
Testing Time
Al Ribbon (low) Temperature Elevation
Wire/ribbon break
Heel failure
Bond lift-off
0%
25%
50%
75%
100%
Initial 500 hours 1,000 hours
Failu
re M
ode
Perc
enta
ge
Testing Time
Al Ribbon (high) Temperature Elevation
Wire/ribbon break
Heel failure
Bond lift-off
21
Responses to Previous Year Reviewers’ Comments
The reviewer requested that the summary provide general observations and conclusions.
Knowledge transfer of failure modes to industry is a key milestone of this project.
… it was unclear to the reviewer how ultrasonic ribbon bonding labor and new equipment costs compares to standard wire bonding.
In many cases, wire bonding equipment can be retrofitted to add ribbon bonding capability.
The reviewer suggested that in the future an EV component manufacturer might be added to the collaborators.
Knowledge transfer to manufacturers will be accomplished through industry visits.
22
Collaboration and Coordination
• Partners o Curamik (Industry): technical partner on substrate design o Kulicke and Soffa (Industry): technical partner on wire and ribbon
bonding procedure
23
Remaining Challenges and Barriers
• The design-of-experiments required to cover all combinations is large: o Strategically choosing key experiments reduces
the overall set of combinations. o Sought experience from the technical community
to guide our choices in experimental tests and ribbon bonding geometries.
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Proposed Future Work (FY14)
• Complete thermal, power, and environmental testing on ribbon bonds.
• Report on mechanical reliability of ribbon bonds under testing, and make recommendations to industry partners.
• Validate lifetime estimation models for specific failure modes observed in accelerated tests.
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Summary • DOE Mission Support:
o Transitioning from wire bonding to ribbon bonding manufacturing will advance power electronics technology for compact, reliable packaging with higher current capabilities.
• Approach: o Synthesize ribbon bonds with varying material (Al, Cu/Al) and geometry
(cross section, span and loop height, pad length, number of stitches, stacked pads, and forced angles) parameters.
o Conduct comprehensive reliability testing, including temperature elevation, temperature cycling, power cycling, and corrosion testing.
o Revise wire bond models to be applicable to ribbon bonding. • Accomplishments:
o Test samples were synthesized, and reliability testing was initiated. o Initial accelerated tests and interconnect bond strength evaluations were
completed.
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Summary • Collaborations:
o Curamik, Kulicke and Soffa • Future Work:
o Complete thermal, power, and environmental testing on ribbon bonds. o Report on mechanical reliability of ribbon bonds under testing and make
recommendations to industry partners. o Validate lifetime estimation models for specific failure modes observed in
accelerated tests.
For more information, contact:
Principal Investigator Douglas DeVoto [email protected] Phone: (303) 275-4256 APEEM Task Leader
Sreekant Narumanchi [email protected] Phone: (303) 275-4062
Acknowledgments:
Susan Rogers and Steven Boyd, U.S. Department of Energy Team Members:
Paul Paret Tao Xu (K&S)