Copper Wire Packaging Reliability for Automotive and High ... · Copper Wire Packaging Reliability...
Transcript of Copper Wire Packaging Reliability for Automotive and High ... · Copper Wire Packaging Reliability...
External Use
TM
A u g . 1 1 . 2 0 1 5
Copper Wire Packaging Reliability for Automotive and High Voltage
Tu Anh Tran | AMPG Package Technology Manager
TM
External Use 1
Agenda• New Automotive Environments• Wire Bond Interconnect Selection• Challenge in High Temperature Bake • Challenge in Temperature Cycling• Challenge in Moisture and High Voltage Testing• Freescale Copper Wire Strategy and Progress• Summary
TM
External Use 2
New Automotive Environments
TM
External Use 3
Automotive Microcontrollers Product Portfolio
TM
External Use 4
More Challenging Powertrain Applications
Previous Under the Hood Application Profile
New Under the Hood Application Profile
Junction Temperature (ºC)
Duration (hours)
150 50145 150135 1,200120 4,600Total 6,000
Junction Temperature (ºC)
Duration (hours)
150 3,000130 10,000110 7,000Total 20,000
TM
External Use 5
Reaching for a Higher Packaging Certification Level
Certify next-generation multicore automotive controller packages (BGA and Leadframe) to AEC Grade 0, 2X AEC Grade 1.
Package Stress AEC Grade 1 AEC Grade 0
Air-to-air Temperature CyclingAATC (-50/150ºC)
1000 cycles 2000 cycles
High Temp Bake HTB-150ºC 1000 hours 2000 hours
High Temp Bake HTB-175ºC 500 hours 1000 hours
Unbiased HAST-110ºC 264 hoursBiased HAST-110ºC or THB (85ºC / 85%RH)
264 hour HAST or 1008 hour THB
TM
External Use 6
Presentation Focus AreasBGA and LQFP Cross Sections
A
Wire
B
Substrate / LeadframeC
Die Attach
Silicon Die
Epoxy Mold Compound
D
E
Packaging Materials
Focused Areas
Cu Ball Bond Reliability
Cu Wire Bond Compatibility and High Voltage Solder SphereF
AB
C
D E D
AB
C
E
F
TM
External Use 7
Wire Bond Interconnect Selection
TM
External Use 8
High Reliability Wire Bond Interconnect
Freescale selected Pd-Cu wire on Al interconnect for AEC Grade 0.
Al Pad
Au Wire
Cu Wire
Pd-Cu Wire
Al Pad + Ni / Pd / (Au) Over Pad Metallization
Au Wire
Cu Wire
Pd-Cu Wire
Wire Bond Interconnect Options
Au Wire on Al Pad Failing at
1008hr HTB-175°C
Excessive intermetallic compound (IMC) growth leading to Kirkendallvoiding and electrical failure
Pd-Cu Wire on Al Pad Passing at
1008hr HTB-175°C
Minimal IMC growth
TM
External Use 9
Optimizing Pd Coverage for Pd-Cu Ball Bonds
Pd-Cu wire B has best Pd coverage and widest EFO current window.
Pd Coverage on Free Air Balls (FAB) vs. EFO Current for 3 Pd-Cu Wire Types
Pd Coverage on Etched Ball Bonds vs. EFO Current for 3 Pd-Cu Wire Types
TM
External Use 10
Pd-Cu Wire Can Fail HAST with Improper Pd Coverage
Corrosion Layer
Corrosion Layer
Incorrect (High) EFO Current Optimized (Low) EFO Current
Failed 96 hour HAST-130°Cdue to Cu-Al IMC Corrosion
Passed 192 hour HAST-130°C
TM
External Use 11
High Temperature Bake Challenges
TM
External Use 12
Cu Wire Pull Failure Modes in High Temperature Bake
Wire Break (Preferred) Pad Lift (Exposing Barrier or Cu BEOL) Barrier Layer
Ball Lift Exposing Intermetallic Compound (IMC)
Cu-Al IMC
Cu BEOL
Wire Pull Failure Mode Preference:Wire Break > Pad Lift >> Ball Lift
Cu-Al IMC
TM
External Use 13
High Temperature Bake Performance
• 2016 hours/150ºC is not equivalent to 1008 hours/175ºC (AEC G0).• Rate of pad lifts reduced with higher EFO current for Pd-Cu wire.
Decap / Wire Pull Failure Mode DistributionFor Pd-Cu Wire at Different EFO Currents and Bare Cu Wire (Control)
TM
External Use 14
Intermetallic Compound (IMC) Growth and Peripheral Interfacial Crack
• Thicker Cu-Al IMC found on bare Cu.• Longer peripheral interfacial crack above Cu-Al IMC found on bare Cu.
− Interfacial crack resulted in pad lifts or ball lifts in bare Cu. • Pd-Cu wire: Regress IMC formation and delay interfacial crack growth.
Temperature(150°C)
Au - Al 110 X 10-16
Cu - Al 3.18 X 10-16
PdCu - Al 2.89 X 10-16
Intermetallic FormationReaction Rate K (cm2/sec)
TM
External Use 15
Cu Ball Voiding Found in Pd-Cu Wire
• Cu voiding found only with Pd-Cu wire at high bake temperature 175°C and contributed to pad lifting during wire pull.
2016
hou
r H
TB-1
50 °
C20
16 h
our
HTB
-175
°C Cu Voiding
TM
External Use 16
Cu Voiding in Pd-Cu Ball Investigation
• Cu voiding decreased with increasing EFO current.
• Sulfur detected in Cu voiding areas.• No Cl or S detected in Cu-Al IMC.
Spot 1 – Cu, Al, Si, S, O, C
Spot 4 – Cu, Al, Si, S, O, C
Cu Voiding
TM
External Use 17
Cu Voiding in Pd-Cu Ball Mechanism
• After encapsulation, moisture absorbed by the mold compound can cause ions to become mobile, creating a galvanic cell between the Pd and Cu.
• When the Anode (oxidizing metal) area is much smaller than the Cathode (noble metal), the corrosion rate is accelerated.
• We propose that the driving force of this galvanic corrosion is related to Sulfur concentration present in mold compound in HTB-175C.
Pd (Cathode)Examples:
O2 + H2O + 4e- --> 4OH-
2H+ + 2e - H2
Cu (Anode)Cu Cu+ + e -
Cu Cu2+ + 2e -
e- e-e-e-
e-e-e-
e-
e-
e-
e- e-e-e-
e-e-e-
e-
e-
e- e- e-e-e-
e-e-e-
e-
e-
e-
e- e-e-e-
e-e-e-
e-
e-
e- e-
e-e-
e-
e-
e-e-
e-
e-
e-e-
e-
e-
e-e-
e-
Chamfer Squeeze
Low EFO Current(Less Cu Exposure)
High EFO Current(More Cu Exposure)
TM
External Use 18
Reducing Cu Voiding in Pd-Cu Balls
• Reducing Cu voiding in Pd-Cu ball can be achieved by lowering sulfate (adhesion promoter) in mold compound.
• However, Cu voiding shows no reliability risk. Packages passed electrical test at 2016 HTB-175C (2X AEC-G0).
Molding CompoundSO4
= : X PPM
504 HTB-175ºC 1008 HTB-175ºC 2016 HTB-175ºC
Cu Voiding
Molding CompoundSO4
= : 0.25X PPM
TM
External Use 19
Temperature Cycling Challenges
TM
External Use 20
Achieving No Wire-Pull Ball-Lift Failures After Temperature Cycling
• Ball lift after decap / wire pull at 2000 AATC cycles observed on both bare Cu and Pd-Cu wires on Al pad.
• Crack in Al pad caused ball lift during wire pull.
• Assembly process optimized to eliminate ball lift issue after Temperature Cycling.
Cohesive Crack in Al
2000 Cycles of Temperature Cycling
Ball LiftAl and underlying barrier layer
Pd-Cu Ball
Before Optimization After
Crack at Ball Edge
TM
External Use 21
Exceeding AEC Grade 0 Requirement
• Passed electrical test at 2X AEC Grade 0.• Passed decap / wire pull and ball shear at 2X AEC Grade 0 with no
ball lifts.
Ball Shear (gf)
LSL = 2gf for 43um ball diameter
Wire Pull (gf)
JEDEC LSL = 1.8gf for 20um wire
TM
External Use 22
Moisture and High Voltage Challenges
TM
External Use 23
Issues Initial Optimized ResolutionsCu-Al Intermetallic (IMC) bond layer corrosion (biased HAST failure)
• Wire bond process optimization• Internal testing demonstrates higher
pH and lower Cl- are best for CuWB reliability.
• FSL specifies pH and Cl-• FSL tightened MC specification for Au
wire to meet CuWB requirementCorrosion crack
Cu
Al
Solid IMC
Cu
Al
Cu-Al Intermetallic Compound Corrosion in HAST / THB
• Chloride (Cl-), principally from mold compound, can cause corrosion at the Cu ball to IMC interface resulting in open circuits.
• Goal to use same BOM for CuWB and AuWB, including molding compound (MC).
• Internal research developed methods to determine acceptable pH and Cl-levels within ranges specified by suppliers.− Specs often renegotiated with suppliers to allow same MC used for AuWB.− Universal pH and Cl- level spec with reasonable values is not possible. − Acceptable pH and Cl- levels vary among MCs due to other MC attributes.− Acceptable pH and Cl- levels vary with voltage.
TM
External Use 24
Fail
Pass
Low Medium High
Low
Med
ium
Hig
h
≤ 65VPass ≤ 3V
3V
3V
5V
5V Pass ≤ 5V14V
Pass ≤ 3V
Fails
Pass ≤ 65V
Pass ≤ 5V
Pass ≤ 3V
14V Pass ≤ 3V
Pass ≤ 5V
Mold Compound Studies for Cu Wire HAST Compatibility
• pH and Cl- specs are not constant, and are unique for each MC.• Probability of Cu-Al bias HAST corrosion increases with bias voltage.
98 Biased HAST Studies with 19 Mold Compounds across 5 Assembly Sites
TM
External Use 25
Freescale Copper Wire Strategy and Progress
TM
External Use 26
Freescale Strategy: Migrating to Fine Gauge Cu Wires
• 2010-2011:− Strategy: All NPI with Cu wire (except Sensors)− Focus: Non-automotive conversions− Non-automotive production
• 2012:− First automotive conversion− Focus: 2 internal and 1 external factories− First AEC grade 3 production
• 2013:− First automotive production
• 2014 - 2015: Convert entire portfolio to Cu wire− 1 Billion units shipped in April’15− Focus: 2 internal and 5 external factories− >1200 qualifications completed (418 auto / analog quals)− Sensor qualifications started
• Scope:− 17 wafer technologies, 6 wafer fabs, 7 assembly sites− 7 package platforms: Lead frame and Substrate− Bare Cu and Pd-Cu wires
Cu wire bond technology Intellectual Property: − > 40 USA patent applications
filed− > 60 conference presentations
and publications since 2009
TM
External Use 27
General Production Status Update• Production Metrics:
− Cumulative Volume: > 1 Billion across 2 internal and 5 external sites− Automotive: 30%, Consumer/Industrial: 70%− Internal Volume Shipment Mix: > 50% with Cu wire− Quality Incidents: 0.02 ppm
• Qualifications: − 98% of the portfolio qualified− Reliability Tiers: Consumer, Industrial, AEC grade 1 and 0
Freescale Cumulative Cu Wire Volumes
TM
External Use 28
Summary
TM
External Use 29
Summary
• The requirement for next-generation powertrain product packaging is AEC Grade 0 which is 2X the current requirement.
• Freescale package is a cost-effective solution using Pd-Cu wire on Aluminum bond pad meeting and exceeding the challenging AEC Grade 0 packaging reliability requirement.
• Mold compounds were studied and reformulated to accommodate high voltage up to 65 V.
• FSL successfully launched fine gauge Cu wire production to the market including automotive.
TM
© 2015 Freescale Semiconductor, Inc. | External Use
www.Freescale.com