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Lead-Free Flip Chip Assembly

[+] Author Affiliations
Sunil Gopakumar, Vinodh Poyyapakkam, K. Srihari

State University of New York at Binghamton, Binghamton, NY

Dan Blass, Peter Borgesen

Universal Instruments Corporation, Binghamton, NY

Paper No. IMECE2002-39251, pp. 105-109; 5 pages
  • ASME 2002 International Mechanical Engineering Congress and Exposition
  • Electronic and Photonic Packaging, Electrical Systems Design and Photonics, and Nanotechnology
  • New Orleans, Louisiana, USA, November 17–22, 2002
  • Conference Sponsors: Electronic and Photonic Packaging Division
  • ISBN: 0-7918-3648-7 | eISBN: 0-7918-1691-5, 0-7918-1692-3, 0-7918-1693-1
  • Copyright © 2002 by ASME


It is well established that Pb free alloys tend to solder less readily than Sn/Pb. It is not clear that this is always a major problem, but two factors combine to make it more of a concern for flip chip than for other applications. Not surprisingly, wetting and spreading appears to become less effective as the solder volume is reduced and a larger fraction of it is near the surface. At the same time assembly yields tend to become more sensitive to this. The present paper addresses the assembly of flip chips with Sn/Ag/Cu bumps onto Ni/Au and OSP coated copper pads on organic substrates. Soldering defects observed included incomplete wetting and collapse, as well as poor self centering. The sensitivity to fluxes, reflow profiles, and substrate pads were investigated and potential consequences for assembly yields calculated numerically.

Copyright © 2002 by ASME



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