Abstract
In this study, the electromigration (EM) performance of the low cost printed Sn0.7Cu bumps assembled with commonly used immersion tin (IT) surface finished substrate for flip chip application is investigated and compared to the printed EU bumps. The EM experimental measurement and analysis results show the t50 life of printed SnCu0.7 solder joint is 3X better than that printed eutectic SnPb solder joint under 150°C −500mA condition. Two EM failure mechanisms of SnCu0.7 solder joint are observed. One is void formation at current crowding area and crack propagation through Under Bump Metallurgy (UBM) intermetallic (IMC). The other is UBM and IMC depletion when test temperature is increased to 150°C and 160°C; and solder extrusion through the depletion area is found. The effective activation energy for printed SnCu0.7 solder is 1.20 and the exponent associated with current density is 1.47. The reference design suggestions for EM reliability of printed SnCu0.7 solder joint with immersion tin surface finish are provided in this study.
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