Journal of Materials Research

Articles

The microstructure of Sn in near-eutectic Sn–Ag–Cu alloy solder joints and its role in thermomechanical fatigue

Donald W. Hendersona1 c1, James J. Woodsa1, Timothy A. Gosselina1, Jay Barteloa1, David E. Kinga2, T.M. Korhonena3 c1, M.A. Korhonena3, L.P. Lehmana4, E.J. Cottsa4, Sung K. Kanga5, Paul Lauroa5, Da-Yuan Shiha5, Charles Goldsmitha6 and Karl J. Puttlitza6

a1 IBM Corporation, Endicott, New York 13760

a2 Endicott Interconnect Technologies, Endicott, New York 13760

a3 Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853

a4 Physics Department, Materials Science Program, Binghamton University,Binghamton, New York 13902

a5 IBM Corporation, T.J. Watson Research Center, Yorktown Heights, New York 10598

a6 IBM Corporation, Hopewell Junction, New York 12533

Abstract

During the solidification of solder joints composed of near-eutectic Sn–Ag–Cu alloys, the Sn phase grows rapidly with a dendritic growth morphology, characterized by copious branching. Notwithstanding the complicated Sn growth topology, the Sn phase demonstrates single crystallographic orientations over large regions. Typical solder ball grid array joints, 900 μm in diameter, are composed of 1 to perhaps 12 different Sn crystallographic domains (Sn grains). When such solder joints are submitted to cyclic thermomechanical strains, the solder joint fatigue process is characterized by the recrystallization of the Sn phase in the higher deformation regions with the production of a much smaller grain size. Grain boundary sliding and diffusion in these recrystallized regions then leads to extensive grain boundary damage and results in fatigue crack initiation and growth along the recrystallized Sn grain boundaries.

(Received October 23 2003)

(Accepted March 03 2004)

Key Words:

  • Alloy

Correspondence:

c1 Address all correspondence to these authors. e-mail: donwhend@us.ibm.com, tkk3@cornell.edu, lplehman@binghamton.edu

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