Authors: Chris Kinney Xioranny Linares KyuOh Lee JW Morris
Publish Date: 2013/02/09
Volume: 42, Issue: 4, Pages: 607-615
Abstract
The work reported here explores the influence of crystal orientation on the growth of the interfacial intermetallic layer during electromigration in CuSnCu solder joints The samples were thin planar SnAgCu SAC solder layers between Cu bars subject to a uniaxial current Electron backscatter diffraction EBSD was used to characterize the microstructure before and after testing The most useful representation of the EBSD data identifies the Sn grain orientation by the angle between the Sn caxis and the current direction The tested samples included singlecrystal joints with caxis nearly parallel to the current “green” samples and with caxis perpendicular to the current “red” samples At current density of 104 A/cm2 steadystate temperature of ~150°C an intermetallic layer grew at an observable rate in the “green” samples but not in the “red” ones A current density of 115 × 104 A/cm2 temperature ~160°C led to measurable intermetallic growth in both samples The growth fronts were nearly planar and the growth rates constant after an initial incubation period the growth rates in the “green” samples were about 10× those in the “red” samples The Cu concentrations were constant within the joints showing that the intermetallic growth is dominated by the electromigration flux The measured growth rates and literature values for the diffusion of Cu in Sn were used to extract values for the effective charge z that governs the electromigration of Cu The calculated value of z is significantly larger for current perpendicular to the caxis than along it
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