1 / 90

Overview of Flip Chip Research

Overview of Flip Chip Research. Daniel Blass March 2002. Assembly. Lead-Free Assembly Flip Chip in Air Flux Jetting of Liquid No-Clean Fluxes Flip Chip on Flex Reflow Encapsulants Substrate Characterizations Information Needed For Yield Predictions Assembly Yield Software.

karan
Download Presentation

Overview of Flip Chip Research

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Overview of Flip Chip Research Daniel Blass March 2002

  2. Assembly • Lead-Free Assembly • Flip Chip in Air • Flux Jetting of Liquid No-Clean Fluxes • Flip Chip on Flex • Reflow Encapsulants • Substrate Characterizations • Information Needed For Yield Predictions • Assembly Yield Software

  3. Underfilling • Self-Filleting • Solder Extrusions & Trench Solder Mask Openings • Underfill Flow Modeling • Transfer Molding • No Void-Free Process Yet • Reflow Encapsulant Codification • Process Cook-Book / Guide • Underfilling Codification

  4. Reliability • Moisture and Aging • Fillet Cracking Experiments • Crack Growth Experiments and Modeling • Lead-Free Reliability • Pad Finish • Reflow Attach Profile • Additional Reflows/JEDEC Level 3 Test • Transfer Molded Flip Chips • Results Comparable to a Capillary Flow Underfill

  5. High Temp JEDEC Level 3 Testing • Moisture/Reflow Sensitivity Classification for Nonhermetic Solid State Surface Mount Devices • Component Qualification Test • Moisture Load Parts and Reflow 3 Times • Most Lead-Free Alloys Require Much Hotter Reflow Temperatures • Qualify to Higher Reflow Temperatures

  6. Lead-Free Assembly • LF-2 (Sn95.5Ag3.5Cu1.0) from K&S Flip Chip • Liquidus of Approx. 217°C • Previous Process Recommendations • Dip in 2.0 mil of Kester TSF-6522 Flux • Nitrogen Reflow Atmosphere (50 ppm O2) • Peak Reflow Temperature of 238°C to 245°C • 50 to 70 Seconds Above 217°C • Soldering to Ni/Au or Cu-OSP Pads (Entek Plus) • This Process, However, Has Not Given Consistent Defect-Free Assembly • Incomplete Wetting of Pad, Poor Self-Centering • Only One Electrical Open (on Cu-OSP Pads)

  7. Cross-Sections of LF-2 Defects

  8. X-Ray Images of LF-2 Defects

  9. Better Soldering to Ni/Au Pads • 250+ Chips On Each Pad Finish

  10. Most LF-2 Chips Attached to Ni/Au Pads Had No Defects • 250+ Chips On Each Pad Finish

  11. Sample Sizes with Each Process Largest Sample Sizes Built With Profile B or Profile G & 2 mil Kester TSF-6522

  12. Average Defects Per Chip on Each Ni/Au Board Built With Profile B or G & 2 mil of Kester TSF-6522 Flux

  13. Average Defects Per Chip on Each Cu-OSP Board Built With Profile B or G & 2 mil of Kester TSF-6522 Flux

  14. No Clear Profile Preference for Ni/Au Pads

  15. No Clear Profile Preference for Cu-OSP Pads

  16. Large Variation Within Each Process • Limits Ability to Compare Processes that Have Smaller Sample Sizes • Would Have to Build Many More Die To Decide Whether a Reflow Profile Was Better • All Processes Gave Soldering Defects

  17. Thicker Flux Often Gave More Defects • Real Effect or Just Small Sample Sizes? • Good that 1.5 mil of Flux Is Not Worse

  18. Future Direction of Lead-Free Assembly • New “Lead-Free” Fluxes • Heraeus TF69 • Not Suitable for Drum Fluxer: Large Solid Particles • Indium TAC 23 • Kester R903 • Have Not Eliminated Soldering Defects • Flux-Jetting of Liquid No-Clean Fluxes

  19. Future Direction of Lead-Free Assembly • Alternative Finishes • Cu / Omikrontm Immersion White Tin • Cu / AlphaLEVELtm Organo-Metallic Immersion Silver • Electroless Ni / Immersion Silver (ENIS) • Would Likely to Have Same Reliability Issues as Electroless Ni / Immersion Au (ENIG) • Reflow Profile Optimization • Other Alloys? • Limited Soldering Trials with Sn/Ag/Bi • Interest?

  20. Lead-Free Reflow Profiles • Profile Optimization • Lower Soak Temp • Shorter Soak or No Soak • Sharper Spike to Reflow • Longer Time at Peak

  21. Lead-Free Reliability • Pad Finish • Better Reliability on Cu-OSP Pads • Thermal History • Reflow Profile Used to Attach Chips • Additional Reflows • Changes to Fatigue Resistance • Damage to Underfilled System • No Failures Attributed to the Soldering Defects • Solder Fatigue Cracks Are Found Near Chip • Defect Level Does Not Correlate to Failure Time

  22. Poor Correlation of Defect Levels to Failure Time • Dexter FP4549, Cu-OSP Pads, Profiles B & G

  23. Namics U8437-3 Underfill LLTS Results for Chips Attached to Cu-OSP Pads

  24. Namics U8437-3 Underfill LLTS Results for Chips Attached to Ni/Au Pads

  25. Namics U8437-3 Underfill Better Reliability for Chips Attached to Cu-OSP Pads

  26. Solder Joint is Different on Ni/Au Pads • Copper Substitutes Into Ni-Sn Intermetallic Layers • Depletes Copper From Solder • Sn/Ag Joint on Ni/Au Pads • Sn/Ag/Cu Joint on Cu-OSP Pads EDX Map Showing Copper Segregation to Intermetallic Layers Cu Nickel-VanadiumChip UBM NickelSubstrate Pad Sn/Ag

  27. Intermetallic Growth • Parts Supplied By Member of the Consortium • 10 mil Pitch Perimeter Bumped Chip • Ni UBM Layer • Substrates with Ni/Au and Cu-OSP Pads • Chips Bumped With 3 Different Alloys • Sn95.5Ag4.0Cu0.5 different from LF-2 (Sn95.5Ag3.5Cu1.0) • Eutectic Sn/Pb • Sn95.5Ag3.5Bi1.0 (limited supply) • High Temperature Storage Tests • Thermal Cycling

  28. Aging of Sn95.5Ag4.0Cu0.5 Flip Chips • Aging at 125°C • 500 hours • 1000 hours • Little Intermetallic Growth For Chips Attached to Ni/Au Pads • Continued Intermetallic Growth For Chips Attached to Cu-OSP Pads • Both Results Consistent With Previous Investigations for LF-2 (Sn95.5Ag3.5Cu1.0) • Aging at 150°C • 500 hours • 1000 hours

  29. 125°C Aging of Sn95.5Ag4.0Cu0.5 Flip Chip Joints Soldered Cu-OSP As Reflowed 1000 hrs at 125°C

  30. 150°C Aging of Sn95.5Ag4.0Cu0.5 Flip Chip Joints Soldered Cu-OSP 500 hrs at 150°C 1000 hrs at 150°C

  31. Continuing Intermetallic Investigation • Determination of Intermetallic Phase Compositions • At Interfaces • In Bulk Solder • Amount of the Various Phases • Understand the Growth Kinetics • Thermodynamics • Diffusion Mechanisms • Similar Analysis After 500 and 1000 cycles of Air to Air Thermal Cycling • -40°C to 125°C • -40°C to 150°C

  32. LF-2 Reliability after High Temperature JEDEC Level 3 Test • Performed High Temperature JEDEC Level 3 Testing • Peak Temperatures of 244°C and 260°C • Both Namics U8437-3 and Dexter FP4549 Underfills Failed at 260°C • Small Areas of Underfill Delamination at Chip-Underfill Interface • No Popcorning • Decreased LLTS Performance • Change in Solder Properties or Underfill Damage?

  33. Multiple Reflow Experiment • Namics U8437-3 Underfill • Not a JEDEC Level Test • No Moisture Exposure • Profile 250 Used for All Reflows (250°C Peak)

  34. LLTS Results for Ni/Au Padsafter Extra Reflows

  35. LLTS Results for Cu-OSP Padsafter Extra Reflows

  36. Extra Reflows After Underfilling Caused More Delamination in LLTS

  37. Lead-Free Summary • Better Soldering to Ni/Au Pads than to Cu-OSP • No Electrical Opens Caused By Soldering Defects • Either in Assembly or Subsequent Reliability Testing • Yield Concerns for Pad Designs that Give Less Collapse • Concerned About Poor Self-Centering on Cu-OSP Pads • Better Reliability with Cu-OSP Pads than with Ni/Au Pads • Ni/Au Pads Are More Sensitive to Thermal History • Need Better Soldering to Cu-OSP Pads or to an Alternative Non-Nickel Pad Finish

  38. Copper Coated With Shikoku GLICOAT OSP Photoimageable Coverlay Adhesives Base Polyimide Metal Stiffener Flex Circuit Design One Big Coverlay Opening

  39. Flip Chip on Flex • Substrate Design • Work Around Poor Coverlay Tolerances • Large Window Opening to Define Pads • Handling / Fixturing • Want To Keep Die Area Flat During Placement and Reflow • Limit Handling Until Underfill Is Cured • Stiffeners Can Help But Not Lightweight Solution • Stiffeners Can Act As a Spring • Not a Problem with Dip Fluxing • Defects with Reflow Encapsulants Because Some Chips Shifted When Next Chip Was Placed

  40. Flip Chip on Flex • Soldering to the Large Solderable Pads • Often Hear Concerns About “Too Much” Collapse • Shikoku GLICOAT OSP on Copper Pads • Supposed to Limit Solder Wetting to Pad Area • Used Typical Flip Chip Assembly Process • 1.5 to 2.2 mil of No-Clean Paste Flux • SMT Style Profile With Nitrogen (<50ppm O2) • Good Collapse But Gap Still Large Enough to Underfill • Underfilling • Could Not Use Chip Edges for Fiducials • Underfill Sometimes Pooled On Coverlay Without Wetting Edge of Chip

  41. Solder Wetting with 1.5 mil of Kester TSF-6502 Flux Copper Solder

  42. Solder Wetting with 2.2 mil of Kester TSF-6502 Flux • All Copper Covered With Solder

  43. Reflow Encapsulants / No-Flow Underfills • Less Forgiving Approach This Year • Will Not Slow Down Placement Machine • Should Be as Fast as Dip Fluxing in Placement Machine • Wide Solder Reflow Process Window Needed For SMT Integration • Hotter Soak and Peak Temperatures • Standard Placement and Soldering Trials • Designed to Quickly Weed Out Poor Performers Without Assembling Many Chips • Determine Whether a Material Is Worth More Effort • More Work Would Be Needed to Define Process

  44. Reflow Encapsulants • Alpha Fry Technologies NUF 2071E • Dexter Hysol FF2000 • Dexter Hysol FF2200 • Emerson & Cuming 11129-152C (for BGAs & CSPs) • Emerson & Cuming JS11156-24 (for BGAs & CSPs) • Emerson & Cuming XNF1500 • Kester SE-CURE 9101 • Kester LX2-2-13 (SE-CURE 9125) • Loctite X237115 • 3M UF3400 • Sumitomo CRP-4700A • Sumitomo CRP-4750A (30wt% silica filler)

  45. Battery of 10 Profiles for Reflow Encapsulant Soldering Evaluation

  46. Battery of 10 Profiles for Reflow Encapsulant Soldering Evaluation • Soak Stage Temperature • Length of Soak Stage • Peak Reflow Temperature

  47. Reflow Encapsulant Evaluation • Dexter Hysol FF2000 • No Post-Cure Step • No-Soak, Volcano Profile Recommended • Dexter Hysol FF2200 • 5-10 minute Cure at 165°C • May Be Sensitive to Higher Soaks • Good in Previous Reliability Testing • Loctite X237115 • No Post-Cure Step • Gelled in Hotter, Longer Soaks • No Reliability Data

  48. Reflow Encapsulant Evaluation (Cont’d) • Kester SE-CURE 9101 • 30 minute Cure at 160°C • Wide Soldering Window • Good Reliability in Reliability Testing • Needs Most Substrate Bakeout • Kester LX2-2-13 (SE-CURE 9125) • No Post-Cure Step • Soldered OK in All Tested Profiles • No Reliability Data

  49. Reflow Encapsulants Not Recommended • Alpha Fry Technologies NUF 2071E • Voiding Issues (May Need Longer Bakeout) • Weird Reflow Profile • Emerson & Cuming XNF1500 • No Post-Cure • Soldered Great • Reliability Not as Good as Other Materials • 3M UF3400 • Viscous, Needed Slow Placement Times • Sumitomo CRP-4700A • Did Not Cure After Hours at 150°C • Sumitomo CRP-4750A (30wt% silica filler) • Filler Sometimes Prevented Solder Joint Formation

  50. Prebake Studies • Normal Prebake Recommendation For Capillary Underfilling is 2 Hours at 125°C • Conservative, Shorter Prebakes Are Possible • Reflow Encapsulants See Higher Temperatures • Drives More Moisture Out of Board • Needed Prebake Depends on Reflow Encapsulant • Depends on Substrate Design • Copper Planes Under Chip? • Time Between Bakeout and Assembly • Accumulation of Ambient Moisture • Moisture Deep in Board Can Diffuse to Outer Layers

More Related