Mechanical Properties and Fracture Behavior of the Cu and Cu 6 Sn 5 -Dispersed Sn-Pb Solder Bumps Processed by Screen Pr
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Mechanical Properties and Fracture Behavior of the Cu and Cu6Sn5 –Dispersed Sn-Pb Solder Bumps Processed by Screen Printing Ho-Seob Cha, Kwang-Eung Lee, Jin-Won Choi, and Tae-Sung Oh Department of Metallurgical Engineering and Materials Science, Hong Ik University, Seoul 121-791, Korea ABSTRACT
The mechanical properties of the 1-9 vol % Cu and Cu6Sn5-dispersed 63Sn-37Pb solder alloys were characterized with tensile test. Also, the Cu and Cu6Sn5-dispersed 63Sn-37Pb solder bumps of 760 µm size were fabricated on the Au(5 µm)/Ni(5 µm)/Cu(27 µm) BGA substrates by screen printing process, and their shear strength were characterized with variations of the dwell time at the reflow peak temperature(220°C) and aging time at 150°C. The yield strength and ultimate tensile strength of the 63Sn-37Pb solder alloy increased with dispersion of 1-9 vol % Cu and Cu6Sn5. In general, however, the Cu and Cu6Sn5-dispersed solder bumps exhibited lower shear strengths than those of the 63Sn-37Pb solder bumps The failure surface of the solder bumps after ball shear test could be divided into two regions of slow crack propagation and critical crack propagation, and the shear strength of solder bumps was inversely proportional to the slow crack propagation length.
INTRODUCTION
As the demand for the miniaturized electronic devices is explosively increased in the mobile phone industry, efforts have been focused to development of the advanced microelectronic packages in recent years [1-3]. As the size and pitch of the solder bumps decrease rapidly, bumping process to ‘pick and place’ solder balls has reached its limit, various solder bumping processes have been investigated. Among the solder bumping processes such as stencil printing, evaporation, plating, and MJT, stencil printing is considered as one of the most suitable processes in the view of the productivity, production cost, and realization of fine pitch. As the size of the solder bump is miniaturized, the reliability of the package is more and more dependent upon the solder joint reliability [3,4]. To improve the solder joint reliability, the creation of a “composite solder” has been attempted by dispersion of copper-coated carbon fibers and Cu6Sn5 intermetallic compound into the solder matrix [5]. In this study, solder bumps of the Cu and Cu6Sn5-dispersed 63Sn-37Pb solder alloy were fabricated by screen printing process, and the microstructure and shear strength of the Cu and Cu6Sn5-dispersed 63Sn-37Pb solder bumps were characterized with variations of the dwell time at the reflow peak temperature(220°C) and aging time at 150°C.
EXPERIMENTAL DETAILS N3.4.1
Cu6Sn5 powders were fabricated by mechanical alloying of Cu and Sn for 3 hours using Spex mixer/mill. As shown in Fig. 1, mechanical alloying of Cu and Sn powders to Cu6Sn5 powders was completed by vibro-milling for 3 hours.
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Figure 1. XRD patterns of the Cu and Sn powders mixed as Cu6Sn5 composition (a) before and (b) after mechanical alloyin
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