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Material Selection & its Impact on Co-planarity of Spring Pin Probe Head

Material Selection & its Impact on Co-planarity of Spring Pin Probe Head. Dr. Jiachun Zhou (Frank), Frank Liu, Siang Soh Smiths Connectors | IDI. IWLPC November 11- 13, 2014. Contents. Background Material Stiffness & Co-planarity FEA on Probe Head Bowing

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Material Selection & its Impact on Co-planarity of Spring Pin Probe Head

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  1. Material Selection & its Impact on Co-planarity of Spring Pin Probe Head Dr. Jiachun Zhou (Frank), Frank Liu, Siang Soh Smiths Connectors | IDI IWLPC November 11- 13, 2014

  2. Contents • Background • Material Stiffness & Co-planarity • FEA on Probe Head Bowing • Pin Tip Co-planarity vs. Probe Head Bowing • Probe Head Structure & Co-planarity • Cartridge & Frame Structure on PH Bowing • Mounting Structure on PH Bowing • Material Hygroscopic Growth • Summary

  3. Background • Package industry trend: WLCSP, MicroCSP • ≤ 0.3mm pitch • Bump ≤ Ø0.21mm • Ball (BGA) or pad • Test technology requires: • >500K cycle life • Reliable contact • RF performance • Easy maintenance

  4. Background • Spring Contact Probe Head • Successful for WLCSP • Highly compliant • Field serviceable • More reliable contact with larger spring force Top plunger Spring Top side travel Bottom plunger Preload

  5. Spring Contact PH Example • New contactor interposer with Embedded Barrel Spring Probe (EBSP) have been developed for testing small pitch wafer, WLCSP, MicroCSP • Components: • EBSP cartridge • Fan out PCB • Bottom contactor (spring probe, 0.8~1.0mm pitch) EBSP cartridges Fan out PCB Bottom contactor

  6. Background • Major criteria for spring pin PH • True position of pin tip to ensure good alignment to WLCSP bumps • Tip co-planarity to keep reliable contactor on all WLCSP bumps • Major factors to determine tip co-planarity • Component tolerances • Bowing generated by preload of spring pins. Top plunger Spring Top side travel Bottom plunger Preload

  7. Material Stiffness & Co-planarity • Spring pin preload & bowing • ~ 12gf • 20~30% of total spring compliance • Bowing: ~ 50% of total tip co-planarity variation • Less bowing with higher stiffness material (flexural modulus of elasticity)

  8. FEA on PH Bowing • FEA model & PH dimensions Top side

  9. FEA on PH Bowing Material A Material B • FEA results for 4 different materials Material C Material D

  10. Co-planarity & Bowing • Tip co-planarity: • Equal to Max deflection – Min deflection

  11. PH Structure & Co-planarity With frame No frame • Carrier & frame structure • High stiffness frame to reduce bowing Max def: 0.262mm Max def: 0.124mm

  12. PH Structure & Co-planarity • Mounting structure & PH bowing • Less bowing with mounting screws closer to pin array • Limitation by test board components & other structure

  13. Material Hygroscopic Growth • Material expansion by water absorption • True position may vary by the changes of humidity • Dependent by material type, example below

  14. Summary • Spring pin preload in WLCSP probe head affects contactor tip co-planarity significantly. • Higher stiffness material of PH is preferred to reduce bowing for better co-planarity. • Optimal mechanical structure of PH can have less bowing and better co-planarity. • Water absorption rate of material must be considered in material selection due to its potential on true position variation.

  15. Thanks

  16. Background • Vertical Probe Technology • Buckling beam contactor • Excellent cycle life, RF, easy to align • Limited compliance • Significant initial cost • Not field serviceable

  17. Background • Vertical Probe Technology • Buckling beam contactor • Excellent cycle life, RF, easy to align • Limited compliance • Significant initial cost • Not field serviceable

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