Effects of Cooling Rate on the Microstructure and Tensile Behavior of a Sn-3.5wt.%Ag Solder

F. Ochoa, J. J. Williams, Nikhilesh Chawla

Research output: Contribution to journalArticle

165 Scopus citations

Abstract

The tensile behavior and microstructure of bulk, Sn-3.5Ag solders as a function of cooling rate were studied. Cooling rate is an important processing parameter that affects the microstructure of the solder and, therefore, significantly influences mechanical behavior. Controlled cooling rates were obtained by cooling specimens in different media: water, air, and furnace. Cooling rate significantly affected secondary dendrite-arm size and spacing of the Sn-rich phase, as well as the aspect ratio of Ag3Sn. The Sn-rich dendrite-arm size and spacing were smaller for water-cooled specimens than for air-cooled specimens. Furnace cooling yielded a nearly eutectic microstructure because the cooling rate approached equilibrium cooling. The morphology of Ag3Sn also changed from spherical, at a fast cooling rate, to a needlelike morphology for slower cooling. The changes in the microstructure induced by the cooling rate significantly affected the mechanical behavior of the solder. Yield strength was found to increase with increasing cooling rate, although ultimate tensile strength and strain-to-failure seemed unaffected by cooling rate. Cooling rate did not seem to affect Young's modulus, although a clear correlation between modulus and porosity was obtained. The mechanical behavior was correlated with the observed microstructure, and fractographic analysis was employed to elucidate the underlying damage mechanisms.

Original languageEnglish (US)
Pages (from-to)1414-1420
Number of pages7
JournalJournal of Electronic Materials
Volume32
Issue number12
DOIs
StatePublished - Dec 2003

Keywords

  • Cooling rates
  • Lead-free solder
  • Microstructure
  • Sn-3.5Ag
  • Tensile behavior

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Electrical and Electronic Engineering
  • Materials Chemistry

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