Microstructure and intermetallic growth effects on shear and fatigue strength of solder joints subjected to thermal cycling aging

Microstructure development of eutectic solder alloy (63Sn/37Pb) after therm al cycling aging and its impact on the shear and fatigue failure of the sol der joint has been investigated. The solder microstructure changes with the reflow process and subsequent thermal cycling environments in solder joint reliability tests from - 40 to 125 degreesC. In service, solder joints are subjected to thermal cycling aging, corresponding to power on-off cycling of the electronic equipment or cyclic environmental temperature loading, le ading to thermal fatigue failures. Thus, it is important to study the effec t of the microstructure changes, mechanical strength and fatigue resistance of solder before and after thermal cycling aging. A new specimen design ha s been developed to closely resemble the actual electronic packaging assemb ly condition. The joint is made simply by soldering a solder ball between t wo FR-4 substrates with copper pads using the reflow process. The study sho ws that the solder microstructure coarsened and intermetallic compound laye rs grew after 500, 1000 and 2000 thermal cycles. The shear and fatigue stre ngth of the solder joint decreased with increased exposure to thermal cycli ng aging effects. (C) 2001 Elsevier Science B.V. All rights reserved.