Nonuniform and negative marker displacements induced by current crowding during electromigration in flip-chip Sn-0.7Cu solder joints

S. W. Liang, Hsiang Yao Hsiao, Chih Chen*, Luhua Xu, King-Ning Tu, Yi Shao Lai

*Corresponding author for this work

Research output: Contribution to journalArticle

5 Scopus citations

Abstract

A quantitative analysis of the nonuniform distribution of current density and nonuniform rate of electromigration has been carried out by measuring the movement of an array of diffusion markers. Tiny marker arrays were fabricated by focused ion beam on the polished surface of flip-chip solder joints near the anode to measure the electromigration rate. The marker velocity at the current-crowding region was found to be at least five times larger than at locations far from the region. Some of the markers in the low-current-density region possess negative velocities, indicating that backflow occurs during the electromigration. The backflow, in which the atomic flow is against the electron flow, is explained by a constant-volume model as well as the back-stress induced by electromigration.

Original languageEnglish
Pages (from-to)2443-2448
Number of pages6
JournalJournal of Electronic Materials
Volume38
Issue number12
DOIs
StatePublished - 1 Dec 2009

Keywords

  • Electromigration
  • Pb-free solder

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