Journal of Electronic Materials

, Volume 38, Issue 11, pp 2234–2241 | Cite as

Fundamental Study of the Intermixing of 95Pb-5Sn High-Lead Solder Bumps and 37Pb-63Sn Pre-Solder on Chip-Carrier Substrates

Article
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Abstract

This study investigated the intermixing of 95Pb-5Sn solder bumps and 37Pb-63Sn pre-solder in flip-chip solder joints. The reaction conditions included multiple reflows (up to ten) at 240°C, whereby previously solder-coated parts are joined by heating without using additional solder. We found that the molten pre-solder had an irregular shape similar to a calyx (i.e., a cup-like structure) wrapped around a high-lead solder bump. The height to which the molten pre-solder ascended along the solid high-lead solder bump increased with the number of reflows. The molten pre-solder was able to reach the under bump metallurgy (UBM)/95Pb-5Sn interface after three to five reflows. The molten pre-solder at the UBM/95Pb-5Sn interface generated two important phenomena: (1) the molten solder dewetted (i.e., flowed away from the soldered surface) along the UBM/95Pb-5Sn interface, particularly when the number of reflows was high, and (2) the molten pre-solder transported Cu␣atoms to the UBM/95Pb-5Sn interface, which in turn caused the Ni-Sn compounds at the chip-side interface to change into (Cu0.6Ni0.4)6Sn5.

Keywords

High-lead solder composite solder flip chip 
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Copyright information

© TMS 2009

Authors and Affiliations

  • C. C. Chang
    • 1
  • Y. W. Lin
    • 1
  • Y. S. Lai
    • 2
  • C. R. Kao
    • 1
  1. 1.Department of Materials Science and EngineeringNational Taiwan UniversityTaipeiTaiwan
  2. 2.Advanced Semiconductor Engineering, Inc.Kaohsiung CityTaiwan

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