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Flip Chip Assembly in Air

Flip Chip Assembly in Air. Antonio Prats March 2002. Very low oxygen levels in reflow allow good yields over a wide range of conditions Unfortunately, nitrogen can be expensive in certain regions Reflow in nitrogen can increase the chance of tombstoning with small 0201 and 0402 components

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Flip Chip Assembly in Air

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  1. Flip Chip Assembly in Air Antonio Prats March 2002

  2. Very low oxygen levels in reflow allow good yields over a wide range of conditions Unfortunately, nitrogen can be expensive in certain regions Reflow in nitrogen can increase the chance of tombstoning with small 0201 and 0402 components It would be nice to have an air reflow process for flip chip assembly Flip Chip Assembly in Air

  3. Universal Consortium Flip Chip Test Substrate Trench and Pads Trench and Pads

  4. Air Reflow ProfilesProfile A was Also Run with 1000 ppm Oxygen

  5. Paste Fluxes • Liquid Fluxes • Manufacturer • Product • Manufacturer • Product • Almit • BM1-RMA • Almit • BM1-RMA-5000 • Alpha Metals • CF2400 • Almit • RC-15 • Heraeus • TF-38 • Alpha Metals • 9171 • Indium • FC-NC-HT-C • Heraeus • CL84 - 7897 • Indium • FC-NC-LT-C • Indium • FC-NC-HT-B • Indium • FC-NC-LT-D • Indium • FC-NC-LT-B • Indium • TAC23 • Kester • KS17-99B-1 • Kester • 9603 • Kester • KS17-99B-2 • Kester • R903 • Kester • TSF-6502 • Kester • TSF-6522 Paste Fluxes and Liquid Fluxes

  6. Alpha Metals CF2400, Hot Air Very Poor Soldering 3.7 mil Heraeus TF38, Cool Air

  7. Poor Soldering Indium FC-NC-LT-C, Hot 1010 ppm Oxygen Exposed Gold

  8. No Electrical Failures but Poor Soldering Almit BM1-RMA-NC, Cool Air

  9. No Electrical Failures but Poor Soldering Indium TAC023, Hot Air Exposed Gold

  10. 2.6 mil Good Soldering Almit BM1-RMA-NC, Hot 985 ppm Oxygen Indium TAC023, Cool Air Kester R903, Cool Air

  11. Hot Profile in Air <none> Hot Profile with 1000 ppm Oxygen Indium TAC023 Cool Profile in Air Kester R903 Almit BM1-RMA-NC Alpha Metals CF2400 Indium TAC023 Kester 9603 Kester R903 Fluxes that Exhibited Good Soldering Hot Profile: Peak 228°C, end of soak 168°C Cool Profile: Peak 210°C, end of soak 152°C

  12. Jet Dispensing of Liquid Fluxes for Flip Chip Assembly Antonio Prats March 2002

  13. In the past, spray fluxing of water-soluble or no-clean liquid fluxes did not offer a robust assembly process It is time to re-evaluate liquid fluxes and look at the Asymtek Dispense Jet process Jet Dispensing of Liquid Fluxes for Flip Chip Assembly

  14. Piston is Seated Piston Retracts, Flux Fills Piston Returns, Forces Material Out, Followed by Air Jet Dispensing of Liquid Fluxes for Flip Chip Assembly

  15. Dispense Pattern for Jetted Flux

  16. Some Fluxes Volatilize Quickly Only one leaves behind a tacky film (Alpha Metals 9171) The rest leave a non-tacky film that does not hold a flip chip in place Other Fluxes Do Not These fluxes remain fluid through die placement Jet Dispensing of Liquid Fluxes for Flip Chip Assembly

  17. Volatile Liquid Fluxes • Less Volatile Fluxes • Manufacturer • Product • Manufacturer • Product • Almit • RC-15 • Almit • BM1-RMA-5000 • Alpha Metals • 9171 (tacky) • Heraeus • CL84 - 7897 • Kester • KS17-133B • Indium • FC-NC-HT-B • Kester • KS19-77A • Indium • FC-NC-LT-B • Senju • ZR-102F • Kester • KS17-99B-1 • Kester • KS17-99B-2 List of Liquid Fluxes That Were Evaluated “Volatile” fluxes are those which dried before the die could be placed. The other fluxes remained liquid for die placement.

  18. Air Reflow ProfilesFluxes Showed No Preference

  19. Indium FC-NC-LT-B, 1010 ppm Oxygen Residue and Some Bridging with Liquid Fluxes Almit BM1-RMA-5000, cool air

  20. Alpha Metals 9171Flux Residue Varies from “Excessive” to “Very Little”

  21. Summary • A good liquid flux will: • Promote good soldering without solder bridges • Hold the die in place through reflow • By remaining liquid or • By volatilizing and leaving behind a sufficiently tacky film • Not leave excessive amounts of residue • We should be able to dispense less flux, and see what effect that has upon the amount of residue • At this time, we have no information on underfill compatibility with these fluxes. This will be very important.

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