Copper Wire Packaging Reliability for Automotive and High Voltage Tu Anh Tran AMPG Package Technology Manager Aug.11.2015 TM External Use
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 External Use 1
New Automotive Environments External Use 2
Automotive Microcontrollers Product Portfolio External Use 3
More Challenging Powertrain Applications Previous Under the Hood Application Profile Junction Temperature (ºC) 150 50 145 150 Duration (hours) 135 1,200 120 4,600 Total 6,000 New Under the Hood Application Profile Junction Temperature (ºC) Duration (hours) 150 3,000 130 10,000 110 7,000 Total 20,000 External Use 4
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 Cycling AATC (-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 Biased HAST-110ºC or THB (85ºC / 85%RH) 264 hours 264 hour HAST or 1008 hour THB External Use 5
Presentation Focus Areas D BGA and LQFP Cross Sections E D E C B A A B C F Packaging Materials A B C D E F Silicon Die Die Attach Substrate / Leadframe Wire Epoxy Mold Compound Solder Sphere Cu Ball Bond Reliability Focused Areas Cu Wire Bond Compatibility and High Voltage External Use 6
Wire Bond Interconnect Selection External Use 7
High Reliability Wire Bond Interconnect Wire Bond Interconnect Options Al Pad Au Wire on Al Pad Failing at 1008hr HTB-175 C Au Wire Cu Wire Pd-Cu Wire Al Pad + Ni / Pd / (Au) Over Pad Metallization Pd-Cu Wire on Al Pad Passing at 1008hr HTB-175 C Au Wire Cu Wire Pd-Cu Wire Excessive intermetallic compound (IMC) growth leading to Kirkendall voiding and electrical failure Minimal IMC growth Freescale selected Pd-Cu wire on Al interconnect for AEC Grade 0. External Use 8
Optimizing Pd Coverage for Pd-Cu Ball Bonds 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 Pd-Cu wire B has best Pd coverage and widest EFO current window. External Use 9
Pd-Cu Wire Can Fail HAST with Improper Pd Coverage Incorrect (High) EFO Current Optimized (Low) EFO Current Corrosion Layer Corrosion Layer Failed 96 hour HAST-130 C due to Cu-Al IMC Corrosion Passed 192 hour HAST-130 C External Use 10
High Temperature Bake Challenges External Use 11
Cu Wire Pull Failure Modes in High Temperature Bake Wire Break (Preferred) Pad Lift (Exposing Barrier or Cu BEOL) Barrier Layer Cu BEOL Ball Lift Exposing Intermetallic Compound (IMC) Cu-Al IMC Cu-Al IMC Wire Pull Failure Mode Preference: Wire Break > Pad Lift >> Ball Lift External Use 12
High Temperature Bake Performance Decap / Wire Pull Failure Mode Distribution For Pd-Cu Wire at Different EFO Currents and Bare Cu Wire (Control) 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. External Use 13
Intermetallic Compound (IMC) Growth and Peripheral Interfacial Crack Intermetallic Formation Reaction Rate K (cm 2 /sec) Temperature (150 C) Au - Al 110 X 10-16 Cu - Al 3.18 X 10-16 PdCu - Al 2.89 X 10-16 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. External Use 14
Cu Ball Voiding Found in Pd-Cu Wire 2016 hour HTB-150 C 2016 hour HTB-175 C Cu Voiding Cu voiding found only with Pd-Cu wire at high bake temperature 175 C and contributed to pad lifting during wire pull. External Use 15
Cu Voiding in Pd-Cu Ball Investigation Cu Voiding Spot 1 Cu, Al, Si, S, O, C Cu voiding decreased with increasing EFO current. Sulfur detected in Cu voiding areas. No Cl or S detected in Cu-Al IMC. Spot 4 Cu, Al, Si, S, O, C External Use 16
Cu Voiding in Pd-Cu Ball Mechanism Chamfer Squeeze e ē - e-e- e-e- Cu (Anode) Cu Cu + + e Cu Cu 2+ + 2 ē - e ē - e-e- e ē - e-e- Low EFO Current (Less Cu Exposure) Pd (Cathode) Examples: O 2 + H 2 O + 4 --> 4OH - 2H + + 2 H 2 e- High EFO Current (More Cu Exposure) 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. External Use 17
Reducing Cu Voiding in Pd-Cu Balls 504 HTB-175ºC 1008 HTB-175ºC 2016 HTB-175ºC Molding Compound SO 4 = : X PPM Cu Voiding Molding Compound SO 4 = : 0.25X PPM 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). External Use 18
Temperature Cycling Challenges External Use 19
Achieving No Wire-Pull Ball-Lift Failures After Temperature Cycling Al and underlying barrier layer 2000 Cycles of Temperature Cycling Ball Lift 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. Crack at Ball Edge Before Optimization Cohesive Crack in Al Pd-Cu Ball After External Use 20
Exceeding AEC Grade 0 Requirement Wire Pull (gf) Ball Shear (gf) JEDEC LSL = 1.8gf for 20um wire LSL = 2gf for 43um ball diameter Passed electrical test at 2X AEC Grade 0. Passed decap / wire pull and ball shear at 2X AEC Grade 0 with no ball lifts. External Use 21
Moisture and High Voltage Challenges External Use 22
Cu-Al Intermetallic Compound Corrosion in HAST / THB Issues Initial Optimized Resolutions Cu-Al Intermetallic (IMC) bond layer corrosion (biased HAST failure) Al Corrosion crack Cu Cu Solid IMC Al 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 requirement 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 Cllevels 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. External Use 23
Mold Compound Studies for Cu Wire HAST Compatibility 98 Biased HAST Studies with 19 Mold Compounds across 5 Assembly Sites Low Medium High 3V 3V 5V Pass 3V Pass 3V 5V 14V 14V Pass 5V Pass 3V Pass 5V Fails Pass 65V 65V Pas s Fail Pass 5V Pass 3V Low Medium High ph and Cl- specs are not constant, and are unique for each MC. Probability of Cu-Al bias HAST corrosion increases with bias voltage. External Use 24
Freescale Copper Wire Strategy and Progress External Use 25
Freescale Strategy: Migrating to Fine Gauge Cu Wires Cu wire bond technology Intellectual Property: > 40 USA patent applications filed > 60 conference presentations and publications since 2009 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 External Use 26
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 External Use 27
Summary External Use 28
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. External Use 29
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