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Accelerated Testing of Flip Chip Underfill - Sensitivity to Aging/Moisture

Accelerated Testing of Flip Chip Underfill - Sensitivity to Aging/Moisture. Nikhil Vichare Graduate Research Associate Department of Systems Science and Industrial Engineering State University of New York at Binghamton Binghamton NY 13902. Experiment.

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Accelerated Testing of Flip Chip Underfill - Sensitivity to Aging/Moisture

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  1. Accelerated Testing of Flip Chip Underfill - Sensitivity to Aging/Moisture Nikhil Vichare Graduate Research Associate Department of Systems Science and Industrial Engineering State University of New York at Binghamton Binghamton NY 13902

  2. Experiment  Performance in cycling is relative measure of degradation in preconditioning • Preconditioning Time, Temperature, Humidity • 72 hours - 6 months • Room temperature - 130oC • Dry N2 - 85%R.H. • No Preconditioning  Subsequent Cycling in Liquid to Liquid Thermal Shock (LLTS) • 5 minutes hold at -55oC and 125oC • 10 seconds transfer time  Measure corner fillet cracking and delamination around bumps v/s number of LLTS cycles

  3. Experiment • 1056 die  4224 corner fillets • 3 underfills • Dexter FP4549 • Namics U8437-3 • Honeywell JM8802 • 2 fluxes • Kester TSF-6522 • Indium NC-SMQ 75 PB08 chips on 62 mil board with Taiyo PSR4000 mask

  4. Effects of Moisture • It is well “established” that moisture exposure may weaken the underfill. • Pressure Cooker Test (PCT) is a common accelerated test of sensitivity to humidity • Also called unbiased HAST • 85% R.H.,130°C, 2 atm.pressure (JESD22-A118) • Is PCT meaningful?

  5. 30 Crack No Crack No Preconditioning Direct LLTS 25 20 144 Hours PCT + LLTS Number of Fillets 72 Hours PCT + LLTS 15 10 5 0 250 500 250 500 250 500 1000 1500 2000 2500 1000 1500 2000 2500 1000 1500 2000 2500 LLTS Cycles Fillet Cracking in Cycling after PCT • Clear effect on subsequent cycling 14-16 mil Thick Namics U8437-3 Fillets (Kester TSF-6522 Flux)

  6. PCT? • Characteristics of damage in cycling after PCT different from • that after other humidity/temperature exposure PCT 72 Hours + LLTS 85°C/85%R.H. 3 Weeks + LLTS • Also discoloration of underfill and solder mask (see poster)

  7. Time/Temperature and/or Moisture has an Effect ! • Faster Cracking of Namics (TSF-6522) after 85°C/30% R.H. 14-16 mil Thick Namics U8437-3 Fillets (Kester TSF-6522)

  8. Crack No Crack 85°C/30%R.H. 30 85°C/85%R.H. 20 Number of Fillets 10 0 250 500 250 500 1000 1500 2000 2500 1000 1500 2000 2500 LLTS Cycles More Moisture is Worse 2 Weeks of Preconditioning of 14-16 mil Thick Namics U8437-3 Fillets (Kester TSF-6522)

  9. Also Faster Delamination from Solder Bumps after Moisture Exposure • After 3 Weeks of 85°C/85% R.H. 250 1000 2000 • Without Preconditioning 1000 2000 3000 Namics U8437-3 (Kester TSF-6522)

  10. Acceleration? • Similar cracking in subsequent cycling for some encapsulant/ flux/ fillet thickness combinations • Example • 3 months aging in ambient  85°C/30%R.H. for 3 weeks • 6 months aging in ambient  85°C/85%R.H. for 3 weeks

  11. Acceleration? • 3 months ambient  85°C/30%R.H. for 3 weeks • Namics(Kester) 14-16 mil fillets

  12. Acceleration? • 3 months ambient  85°C/30%R.H. for 3 weeks • Same material thinner fillets (10-12 mils)

  13. Acceleration? • 3 months ambient  85°C/30%R.H. for 3 weeks • Dexter(Indium) 10-12 mil fillets

  14. Crack No Crack 30 6 Months Ambient 85°C/85%R.H. 3 weeks 20 Number of Fillets 10 0 500 500 1000 1500 2000 2500 1000 1500 2000 2500 LLTS Cycles Acceleration? • 6 months aging in ambient  85oC/85%R.H. for 3 weeks Namics U8437-3 (Kester TSF-6522) 14-16 mils

  15. Acceleration? • 6 months ambient  85°C/85%R.H. for 3 weeks • and 3 months ambient  85°C/30%R.H. for 3 weeks (totally different cracking in subsequent cycling) for other encapsulant/ flux/ fillet thickness combinations

  16. 30 No Crack Crack 20 3 Months Ambient Number of Fillets 85°C-30% R.H. 3 week 10 0 500 500 1000 1500 2000 2500 1000 1500 2000 2500 LLTS Cycles Acceleration? • 3 months ambient  85°C/30%R.H. for 3 weeks • Honeywell (Kester) 12-14 mil fillets Honeywell (Kester) 12-14 mils

  17. NoCrack 30 Crack 85°C-85% R.H. 3 week 20 6 Months Ambient Number of Fillets 10 0 500 500 1000 1500 2000 2500 1000 1500 2000 2500 Acceleration? • 6 months ambient  85°C/85%R.H. for 3 weeks • Dexter (Indium) 10-12 mil Thick Fillets LLTS Cycles Dexter FP4549 (Indium NC-SMQ 75) 10-12 mils

  18. Moisture isn't Everything! • Underfill also weakens with time (even in dry storage) • That’s why we didn't have a single acceleration

  19. Effect of Time As Well • Aging in Nitrogen Cabinet 10-12 mil Thick Namics U8437-3 (Kester TSF-6522)

  20. Effect of Time As Well • Faster Delamination from Solder Bumps • After 3 Months Aging in Nitrogen Cabinet 1000 2000 3000 • Without Preconditioning 1000 2000 3000 Namics U8437-3 (Indium NC-SMQ 75)

  21. Preconditioning Sometimes Decreased Cracking • 85°C/30%R.H. reduces subsequent cracking of Honeywell (Kester) • Effect of time/temperature or moisture? No Preconditioning 10-12 mil Thick Honeywell JM88202 (Kester TSF-6522)

  22. Crack No Crack 30 85°C/30%R.H. 2 Weeks 85°C/85%R.H. 85°C/85%R.H. 20 3 Weeks 2 Weeks 85°C/30%R.H. Number of Fillets 3 Weeks 10 0 250 500 250 500 250 500 250 500 1000 1500 2000 2500 1000 1500 2000 2500 1000 1500 2000 2500 1000 1500 2000 2500 LLTS Cycles More Moisture Increased Cracking • At same temperature / time more moisture (85°C/85%R.H.) is worse in this case 10-12 mil Thick Honeywell JM88202 (Kester TSF-6522)

  23. Moisture Not Always Bad • A little moisture seems to help (same time /temperature) • Dexter (Indium) 8-10 mil fillets

  24. SUMMARY • Moisture and time/temperature each affect underfill properties • Time/temperature may not always be bad (depends on encapsulant) • Sometimes a little moisture reduces subsequent cracking • Relative contribution of time/temperature Vs moisture depends on encapsulant/ flux combination • Design/choice of accelerated test must account for this

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