Copper Wire Packaging Reliability for Automotive and High ... · Copper Wire Packaging Reliability for . Automotive and High Voltage. ... THB (85ºC / 85%RH) 264 hour HAST or . 1008

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Copper Wire Packaging Reliability for Automotive and High Voltage

Tu Anh Tran | AMPG Package Technology Manager

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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

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New Automotive Environments

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Automotive Microcontrollers Product Portfolio

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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

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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

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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

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Wire Bond Interconnect Selection

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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

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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

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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

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High Temperature Bake Challenges

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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

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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)

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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)

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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

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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

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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)

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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

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Temperature Cycling Challenges

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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

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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

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Moisture and High Voltage Challenges

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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.

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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

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Freescale Copper Wire Strategy and Progress

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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

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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

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Summary

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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.

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