Abstract
With the ever-reducing sizes of electronic devices, the problem of electromigration (EM) has become relevant and requires attention. However, only the EM behavior of Sn–Ag solders within the solder joint structure has been focused on thus far. Therefore, in this study, a thin metallic film composed of Sn–3.5Ag (wt.%) was subjected to a current density of 7.77 × 104 A/cm2 at a temperature of 15 °C to test the ability of existing EM models to predict the nucleation and evolution of voids generated by the resulting atomic migration. A computer simulation was then used to compute the coupled current distribution, thermal distribution, and atomic migration problems. It relied on an original random walk (RW) method, not previously applied to this problem, that is particularly well suited for modelling domains that undergo changes owing to the formation of voids. A comparison of the experimental results and computer simulations proves that the RW method can be applied successfully to this class of problems, but it also shows that imperfections in the film can lead to deviations from predicted patterns.
Highlights
With the ever-reducing sizes of electronic devices, the problem of electromigration (EM) has become relevant and requires attention
Most studies have focused on the EM behavior of Sn–Ag solders only within the structure of a solder joint
Zhu et al previously carried out EM tests in a Sn–3.5Ag thin film with the same thin-film structure for the observation of void growth at the cathode[9]; it was found that after EM, the growth path differed from that predicted by the finite element analysis (FEA) simulations
Summary
With the ever-reducing sizes of electronic devices, the problem of electromigration (EM) has become relevant and requires attention. In this study, a thin metallic film composed of Sn–3.5Ag (wt.%) was subjected to a current density of 7.77 × 1 04 A/cm[2] at a temperature of 15 °C to test the ability of existing EM models to predict the nucleation and evolution of voids generated by the resulting atomic migration. Evolving requirements for high speeds, increased functionality and lower weight are forcing circuits to become smaller This results in high current density within solder joints. Yeh et al reported that voids nucleated near the regions where the current was applied and extended across the entire eutectic Sn–Pb solder joints under a current density of 2.25 × 1 04 A/cm[2] at 150 °C6 This is observed in Sn–4.0Ag–0.5Cu solder bumps at a current density of 3.67 × 1 03 A/cm[2] at 146°C7. On the random walk (RW) approach, and by studying the void pattern evolution over an extended time period rather than only at the end of the experiment
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