Flip Chip Assembly in Air Very low oxygen levels in reflow allow good yields over a wide range of conditions



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Flip Chip Assembly in Air


Flip Chip Assembly in Air

  • 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



Universal Consortium Flip Chip Test Substrate



Air Reflow Profiles Profile A was Also Run with 1000 ppm Oxygen



Paste Fluxes and Liquid Fluxes



Very Poor Soldering



Poor Soldering



No Electrical Failures but Poor Soldering



No Electrical Failures but Poor Soldering



Good Soldering



Fluxes that Exhibited Good Soldering



Jet Dispensing of Liquid Fluxes for Flip Chip Assembly



Jet Dispensing of Liquid Fluxes for Flip Chip Assembly

  • 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



Dispense Pattern for Jetted Flux



Jet Dispensing of Liquid Fluxes for Flip Chip Assembly

  • 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


List of Liquid Fluxes That Were Evaluated



Air Reflow Profiles Fluxes Showed No Preference



Residue and Some Bridging with Liquid Fluxes



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



Summary

  • A good liquid flux will:

  • 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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