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OEE and Production Yield Improvements on WLCSP Devices: Case Study Using a Novel Probe Design

OEE and Production Yield Improvements on WLCSP Devices: Case Study Using a Novel Probe Design. Ranauld Perez Johnstech International Minneapolis, Minnesota, USA. Objectives. Share technical insights about a novel approach for production testing of WLCSP devices

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OEE and Production Yield Improvements on WLCSP Devices: Case Study Using a Novel Probe Design

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  1. OEE and Production Yield Improvements on WLCSP Devices: Case Study Using a Novel Probe Design Ranauld Perez Johnstech International Minneapolis, Minnesota, USA

  2. Objectives • Share technical insights about a novel approach for production testing of WLCSP devices • Provide validation and production test results to determine yield and OEE impacts • Provide takeaway notes about best practices in wafer level testing of WLCSP devices

  3. Probe Design Objectives • Approach a solid probe architecture • Achieve repeatable precision landings and mechanical planarity • Off-apex landing to maintain bump planarity • Precision overdrive control

  4. Probe Array Details • 300mm – 500mm bump pitch • Overdrive range of 175mm typ., 5-20 grams/bump • + 15mm probe tip co-planarity • < 50mW CRES

  5. Probe Tip Design for WLCSP Probe Tip Close up Typical Witness Marks

  6. Pre-Production Probe Validation Device Provider Problem Statement and Probe Effectivity

  7. Pre-Production Validation Device Provider Problem Statement: Increase FPY and OEE by reducing major bin failures for a high volume mixed signal SOC BIN 25: THD Test BIN 24: Output Pwr One Full Quarter Data Plot

  8. Probe OD Optimization Pre-test probe setup guidelines provided to device provider test engineering team

  9. Pre-Production Test Results • Wafer 1: 99.7% FPY, 1 Bin25 failure, no Bin 24 failure • Wafer 2: 99.3% FPY, no Bin 25 and Bin 24 failures • Wafer 3: 99.7% FPY, no Bin 25 and Bin 24 failures Wafer No. 3 Datalog Yield Map

  10. Analysis of Probe Validation Results Device Characterization Data for Bin 25 and 24 Test Circuit Model Based on previous device characterization data provided by third party team, there is strong correlation observed for BINs 24 & 25 against Rload and contact resistance CRES

  11. Yield Correlation vs CRES New Probe: Cres_ave = 25.9 mW, 3s = 14.7 mW Original Probe: Cres_ave = 47.9 mW, 3s = 81.1 mW Total Touchdowns = 11.5k

  12. Production Test Validation 24-Wafer Production Lot Test

  13. First Pass Yield Results Average FPY (24 Wafers) = 99.7% • Reduction of Bin 25 failures from historical average of 58.2% to 13% (w/ retest recovery at 13.8% final) • Reduction of Bin 25 failures from 19.9% to zero • Elimination of wafer retests for bin failure recovery

  14. OEE Comparisons • Previous Quarter OEE Data • Production Run Time: 82.2% • Re-screen % of Run Time: 12.5% • Maintenance Time: 15.3% (98% is for probe cleaning) • New Probe OEE Data • Production Run Time: 93.1% • Manual retest downtime: 5.8% of runtime • Maintenance Time: 4.4% (Zero for probe cleaning)

  15. Conclusions and Takeaways • Novel probe system design merits for WLCSP wafer level testing • Consistent and low CRES provides predictable load conditions for critical DUT test requirements • Mechanical features enable wide OD flexibility to optimize landing force • Precision probe guide and tip design minimizes debris buildup and cleaning interval • Production validation FPY and OEE results substantiate new probe design feature sets for high volume production use • Best practices for final wafer level test of WLCSP devices warrants replication of probe environment in characterization phase

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