WLCSP AND FLIPCHIP PRODUCTION USING ELECTROLESS Ni/Au PLATING AND WAFER LEVEL SOLDER SPHERE TRANSFER TECHNOLOGIES TECHNOLOGIES Dr. Elke Zakel Pac Tech GmbH – Packaging Technologies, Inc. Nauen, Germany 14614 Cer t if ied Ce r t if ied ISO ISO 9 0 0 9 0 0 1 : 1 : 2 0 0 2 0 0 0 0 & ISO & ISO TS 1 6 9 4 9 TS 1 6 9 4 9 Co Co n f iden t ial n f iden t ial
Presentation Outline 1. e-Nickel/Gold UBM 2. Solder Sphere Transfer Solder 3. Process Evaluation 4. Flip Chip Sized Bumps UBM 5. Cost Model WLCSP Bump ELECTROLESS ELECTROLESS WAFER LEVEL SOLDER WAFER LEVEL SOLDER Ni/Au PLATING SPHERE TRANSFER 1) Yield 2) Throughput 3) Cost PacLine 3000 ultra -SB² Cer t if ied Ce r t if ied ISO ISO 9 0 0 9 0 0 1 : 1 : 2 0 0 2 0 0 0 0 & ISO & ISO TS 1 6 9 4 9 TS 1 6 9 4 9 Co Co n f iden t ial n f iden t ial
Under Bump Metallization (UBM) UBM Functions: UBM - Under Bump Metallurgy (Most of World) BLM - Bump Limiting Metallurgy (IBM) 1) Solderable surface UBL - Under Bump Layer (Japan) 2) Electro-migration barrier 3) Thermal-migration barrier 4) Increase standoff 5) Current distribution Integrated Circuit (I/O pad) 6) Protect final metal UBM UBM Requirements: 1) Adhesion to pad metal 2) Low stress 3) Low electrical contact resistance 4) Compatibility with probed I/O pads Bump 5) Compatible with bump (SnPb, SnAgCu, SnAu, Epoxy,…) Cer t if ied Ce r t if ied ISO ISO 9 0 0 9 0 0 1 : 1 : 2 0 0 2 0 0 0 0 & ISO & ISO TS 1 6 9 4 9 TS 1 6 9 4 9 Co Co n f iden t ial n f iden t ial
Common Under Bump Metallizations 1) Sputtered: Al/NiV/Cu Delco Electronics “Flex-on-Cap” Ti/NiV/Au, etc… Smaller volumes - research 2) Evaporated: Cr/CrCu/Cu IBM technology from “C4” era 3) Electroplated: Cu Pillar High standoff Au Bump Significant volumes in Japan 4) Printed: Silver Alloys Next generation Nanotechnology R&D 5) Electroless: 5) Electroless: Nickel/Gold Nickel/Gold Lowest cost Lowest cost Nickel/Palladium Wet Chemical Process Batch Process No Photolithography or High Vacuum Processing Used for WLCSP, Flip Chip, ACA Electroless Ni/Au Bump Cer t if ied Ce r t if ied ISO ISO 9 0 0 9 0 0 1 : 1 : 2 0 0 2 0 0 0 0 & ISO & ISO TS 1 6 9 4 9 TS 1 6 9 4 9 Co Co n f iden t ial n f iden t ial
UBM: Process Flow Comparisons 1 2 3 4 5 Sputtered Evaporative Electroplated Printed Electroless (Ti/NiV/Cu) (Cr/CrCu/Cu) (Cu or Au) (Ag) (Ni/Au) 1) Clean Pad Metal 1) Clean Pad Metal 1) Clean Pad Metal 1) Print Metal 1) Plate e-Ni/Au 2) Sputter Ti/NiV/Cu 2) Apply Photoresist 2) Sputter Ti/Cu Seed 3) Apply Photoresist 3) Soft-bake Photoresist 3) Apply Photoresist 4) Soft-bake Photoresist 4) Photo-expose Resist 4) Soft-bake Photoresist 5) Photo-expose Resist 5) Image Reversal Bake 5) Photo-expose Resist 6) Develop Resist 6) Flood Expose 6) Develop Resist 7) Post Bake 7) Post Bake 7) Develop Resist 7) Develop Resist 7) Post Bake 7) Post Bake 8) Plasma Descum 8) Plasma Descum 8) Plasma Descum 9) Wet Etch Cu 9) Evaporate Cr/CrCu/Cu 9) Plate Cu or Au 10) Dump Rinse 10) Solvent Lift Off 10) Dump Rinse 11) Wet Etch NiV 11) Solvent Clean 11) Strip Photoresist 12) Dump Rinse 12) Dump Rinse/SRD 12) Dump Rinse 13) Wet Etch Ti 13) Wet Etch Ti /Cu Seed 14) Strip Photoresist 14) Dump Rinse/SRD 15) Dump Rinse/SRD Ce Cer t if ied r t if ied ISO ISO 9 0 0 9 0 0 1 : 1 : 2 0 0 2 0 0 0 0 & ISO & ISO TS 1 6 9 4 9 TS 1 6 9 4 9 Co Co n f iden t ial n f iden t ial
Electroless Ni/Au Process Flow (Aluminum Based ICs) Silicon, Organics Al 2 O 3 2) Al Etch 1) Pass Clean Incoming 3) Zincate Zn 5) Zincate II 4) Zn Strip Zn - Al Replacement 6) Ni Plate Ni Ni P 6) Ni Plate Cont. 6) Ni Plate Cont. Ni – Zn Replacement Ni/P Autocatalytic Reaction 7) Gold Plate Au Au/Ni replacement reaction Ce Cer t if ied r t if ied ISO ISO 9 0 0 9 0 0 1 : 1 : 2 0 0 2 0 0 0 0 & ISO & ISO TS 1 6 9 4 9 TS 1 6 9 4 9 Co Co n f iden t ial n f iden t ial
Electroless Ni/Au Plating Video Ce Cer t if ied r t if ied ISO ISO 9 0 0 9 0 0 1 : 1 : 2 0 0 2 0 0 0 0 & ISO & ISO TS 1 6 9 4 9 TS 1 6 9 4 9 Co Co n f iden t ial n f iden t ial
Wafer Bumping Bump Functions: 1) Electrical Interconnect 2) Thermal Interconnect 3) Passive Alignment Integrated Circuit (Pad I/O) UBM Bump Requirements: 1) Adhesion to UBM 2) Low electrical resistance Bump 3) High thermal conductivity 4) Stable intermetallic with UBM Cer t if ied Ce r t if ied ISO ISO 9 0 0 9 0 0 1 : 1 : 2 0 0 2 0 0 0 0 & ISO & ISO TS 1 6 9 4 9 TS 1 6 9 4 9 Co Co n f iden t ial n f iden t ial
Wafer Bumping - Flip Chip & WLCSP Terms used to describe wafer bumping: Flip Chip Flip Chip C4 Flex-on-Cap Solder Interconnect Solder is <200 m m tall FCOB (Flip Chip On Board) Underfilled during assembly C4NP Bumping Bumping WLCSP Wafer Bumping Solder Bumping DCA (Direct Chip Attach) Micro BGA Ultra CSP Solder is >200 m m tall CSP No underfill WLCSP Cer t if ied Ce r t if ied ISO ISO 9 0 0 9 0 0 1 : 1 : 2 0 0 2 0 0 0 0 & ISO & ISO TS 1 6 9 4 9 TS 1 6 9 4 9 Co Co n f iden t ial n f iden t ial
Stencil Print Ball Drop Laser Jet Sphere Transfer Reflow Vacuum Laser Align Stencil Align Stencil Capillary Sphere Reservoir Pick up Spheres Squeegee Drop Balls & Reflow Drop Balls Print Paste Align to Wafer Raise Stencil Raise Stencil Lower Spheres Reflow Reflow Raise Head Reflow Cer t if ied Ce r t if ied ISO ISO 9 0 0 9 0 0 1 : 1 : 2 0 0 2 0 0 0 0 & ISO & ISO TS 1 6 9 4 9 TS 1 6 9 4 9 Co Co n f iden t ial n f iden t ial
Solder Deposition: Process Flow Comparisons WLCSP Flip Chip Stencil Print Ball Drop Solder Jet Wafer Level Wafer Level Solder Paste Solder Sphere Solder Sphere Transfer Transfer (Flip Chip) (CSP) 1) Paste Print 1) Flux 1) Solder Jet & Reflow 1) Flux 1) Flux/Drop/Reflow/Inspect/Rework 2) Reflow 2) Drop 2) Inspect 2) Transfer 2) Clean / SRD 3) Clean / SRD 3) Reflow 3) Reflow 4) Inspect 4) Clean / SRD 4) Clean / SRD 5) Inspect 5) Inspect 5) Inspect 5) Inspect Ce Cer t if ied r t if ied ISO ISO 9 0 0 9 0 0 1 : 1 : 2 0 0 2 0 0 0 0 & ISO & ISO TS 1 6 9 4 9 TS 1 6 9 4 9 Co Co n f iden t ial n f iden t ial
Wafer Level Solder Sphere Transfer (Gang Ball Placement) Vacuum Head Lowered into Solder Spheres in Reservoir Solder Spheres Attached on Solder Spheres Reservoir Vacuum Tooling Plate Align tooling with Wafer Removing Excess Solder (via double vision camera) Spheres via Air Knife Lower Head onto Wafer and Bring Raise Transfer Head Remove Wafer for Reflow and Spheres into Contact with I/O Pads Clean Cer t if ied Ce r t if ied ISO ISO 9 0 0 9 0 0 1 : 1 : 2 0 0 2 0 0 0 0 & ISO & ISO TS 1 6 9 4 9 TS 1 6 9 4 9 Co Co n f iden t ial n f iden t ial
Wafer Level Solder Sphere Transfer Video (Gang Ball Placement) Ce Cer t if ied r t if ied ISO ISO 9 0 0 9 0 0 1 : 1 : 2 0 0 2 0 0 0 0 & ISO & ISO TS 1 6 9 4 9 TS 1 6 9 4 9 Co Co n f iden t ial n f iden t ial
Process Evaluation – Wafer Level Solder Sphere Transfer Process Step Equipment Yield Wafers/Hr 1. UBM Deposition e-Ni/Au (PacLine 3000) 2. Flux Deposition Spin Coater (Spin Pac SC200) 3. Sphere Transfer Basic WLSST Tool (Ultra-SB 2 ) 4. Reflow Linear Oven (Sikama) 5. Wafer Clean Solvent Clean (MegaPac MP300) 6. Inspection Microscope (Olympus MX50) 1) Yield 2) 2) Throughput Throughput Test Vehicle Properties Test Vehicle Properties Wafer Size 200 mm Wafer Thickness 360 µm Die per wafer 3175 I/O per die 25 I/O on the wafer (bumped) 79,375 Pad Size 240 µm Pad Pitch 500 µm Pad Metallurgy Al w/0.5%Cu Ce Cer t if ied r t if ied ISO ISO 9 0 0 9 0 0 1 : 1 : 2 0 0 2 0 0 0 0 & ISO & ISO TS 1 6 9 4 9 TS 1 6 9 4 9 Co Co n f iden t ial n f iden t ial
Process Evaluation – Wafer Level Solder Sphere Transfer Process Step Equipment Yield Wafers/Hr 1. UBM Deposition e-Ni/Au (PacLine 3000) 100 50 2. Flux Deposition Spin Coater (Spin Pac SC200) 3. Sphere Transfer Basic WLSST Tool (Ultra-SB 2 ) 4. Reflow Linear Oven (Sikama) 5. Wafer Clean Solvent Clean (MegaPac MP300) 6. Inspection Microscope (Olympus MX50) Ni/Au Plating Parameters/Results Al Bond Pad Ni/Au Plated Pad Nickel Thickness 5 µm Gold Thickness Gold Thickness 600 Å 600 Å Ni/Au Plating Time (50 per batch) 55 min Throughput 50 wafers/hr Plating Yield 100 % Cer t if ied Ce r t if ied ISO ISO 9 0 0 9 0 0 1 : 1 : 2 0 0 2 0 0 0 0 & ISO & ISO TS 1 6 9 4 9 TS 1 6 9 4 9 Co Co n f iden t ial n f iden t ial
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