Influence of indium addition on electromigration behavior of solder joint
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Keun-Soo Kim Fusion Technology Lab., Hoseo University, Asan 336-795, Korea
Katsuaki Suganuma Institute of Science and Industrial Research, Osaka University, Osaka 567-0047, Japan (Received 18 April 2011; accepted 11 August 2011)
The electromigration (EM) behavior of the Cu/Sn–In/Cu solder model strip was investigated under the conditions of high electrical current density (10 kA/cm2) at various temperatures. The composition of indium (In) was 0, 4, 8, and 16 in wt%. The interconnection of Sn–In solder alloys with a Cu substrate was prepared by reflow soldering at 250 °C. Microstructural analysis confirmed that primary intermetallic compound formed at the interface of the Cu/Sn–In strip was Cu6(In,Sn)5 regardless of In contents. Sn grain size became finer as In content increased. After current stressing, electrical failure was caused by the formation of voids and cracks at the cathode because of the migration of Cu atoms. Sn–16In alloy that has fine grain structure exhibits excellent EM resistance primarily due to the retardation of Cu migration.
I. INTRODUCTION
Miniaturization of electronic packages has emerged as one of the key technologies in the electronic industries. It can provide abundant functionality into small and thin devices. This rapid growth has highlighted the need to ensure that these devices meet certain minimum criteria for reliability. One of the critical reliability issues is the influence of the miniaturization of electronic devices. Interconnections required in these devices keep becoming smaller, resulting in significant increase of current density within each solder joint. Moreover, owing to the difference in the electrical resistance and the feature size between each solder and its adjacent trace, there arises a drastic increase in the current density at the solder joint area. This increased current density will cause an increased massive migration of metal atoms in the direction of electron flow, which is a phenomenon known as electromigration (EM). Directional atomic migration can induce significant microstructural changes in a solder joint, such as voids formation, crack propagation, phase separation, solder extrusion/whiskers, the growth of intermetallic compounds (IMC), and the dissolution of under bump metallization (UBM).1–4 Severe microstructural changes result in an early electrical failure of solder joints. Recently, numerous investigations have been performed regarding to the EM behavior in various solder joints, i.e., Sn–Pb,5 Sn–Ag–Cu,6,7 Sn–Zn,8,9 and Sn–Bi10,11 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.283 2624
J. Mater. Res., Vol. 26, No. 20, Oct 28, 2011
http://journals.cambridge.org
Downloaded: 20 Mar 2015
solder alloys. From the previous literature, the rapid consumption of UBM has been found to pose a critical problem during EM5,7,12,13 and the dissolution rate of UBM layers such as Ni and Cu was also dependent on the crystallographic orientation of Sn,6,14 which has highly anisotropic properties. Numerous rel
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