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The continuous improvement of electronic device performances and the advancement of packaging technology have brought greater challenges to the reliability of solder joints in integrated circuits (ICs). In view of the increase of chip integration and the reduction of micro-bump size in 3D ICs, the high current density and excessive Joule heat will result in serious reliability issues of electromigration (EM) and thermomigration (TM) respectively, which evidently shorten the lifetime of solder joints. This article reviewed the influence of EM, TM and their coupling effect on microstructure evolution and properties of different joints soldered with pure Sn, SnAgCu, SnBi and SnZn solder. What's more, the increase of EM and TM resistances of micro-joints by microalloying, particle reinforcement and substrate improvement was explored. Finally, the shortcomings of current studies and the future research directions were summarized to further improve the EM and TM reliability of micro-joints, which promotes the application of lead-free solders in 3D ICs package.

A novel fabrication process for a high-aspect-ratio recording and stimulation intracortical neural microelectrode array is described. Using a combination of dicing and KOH wet-etching, microspikes are formed on the surface of a n-type (100), 4 mm thick, silicon wafer. Deep 3 mm cuts are performed in order to produce sharped tip pillars of high-aspect-ratio (0.2x0.2x3 mm). Thermomigration is employed as a selective doping technique performing electrically insulated pillars due to the pn back biased junctions formed between each pair of n-type substrate and p+ migrated trails. Gold is deposited over the spikes in order to have a good ionic interface with the neural tissue, while the remaining surface is passivated with a biocompatible layer of cyanoacrylate. The final result is a deep penetrating electrode array with potential new applications in neuroprosthetics’ research field., Fundação para a Ciência e a Tecnologia (FCT) - FCOMP 01 0124-FEDER-010909, FCT/PTDC/SAU-BEB/100392/2008

Electromigration is a major road block on the way to realization of nanoelectronics. Determination of plastic deformation under high current density is critical for prediction of electromigration failure. A new displacement–diffusion coupled model is proposed and implemented using finite element method. The model takes into account viscoplastic behavior of solder alloys, as a result, vacancy concentration evolution and electromigration process are accurately simulated. Finite element simulations were performed for lead-free solder joints under high current density and compared with experimental moire interferometry measurements. The comparison validates the model.

Electromigration and thermomigration behaviors of eutectic tin-lead solder joints were studied above 100 degC with the currents ranging from 1.6 A to 2.0 A. The local temperature of the chip was deducted according to temperature coefficient of resistance. Also, this temperature was inspected by a thermal infrared mapping technique. It is suggested that the heat accumulation within first-level solder interconnections was highly related to the current density. During the electromigration process, Pb migration was apparently visible because of its faster diffusivity. Meanwhile, voids were initiated at the entry location of the electron flow due to the current crowding effect. Numerical simulation also predicted a local current density of above 105 A/cm2 within the solder joint In the thermomigration process, the transport of Pb was detected owing to the thermal gradient across the solder joint. Voids also occurred at the contact window due to accelerated atomic diffusion. In addition, the effect of electromigration and thermomigration on the mechanical behavior of the solder joint was examined through shearing tests.

Metal migration by driving force of electron-flow and temperature gradient is a major reliability concern in power integrated circuits, especially for advanced integrated circuits where there are increasing density of the integrated power components and power dissipation. In this paper, we present a study of the combined effects of electromigration and thermomigration. A special test chip is designed for this study, in which several on-chip heater elements and temperature sensor are realized to impose and measure a temperature gradient, respectively. Our experimental results show that the electromigration lifetimes are much shorter in the presence of a temperature gradient than in a uniform temperature. The shortening of the electromigration lifetimes can be attributed to the effect of temperature gradient on electromigration-induced failure, rather than an additional driving force by thermomigration (due to a temperature gradient). Our observation is in qualitative agreement with recent theoretical model.

Metal migration by driving force of electron-flow and temperature gradient is a major reliability concern in power integrated circuits, especially for advanced integrated circuits where there are increasing density of the integrated power components and power dissipation. In this paper, we present a study of the combined effects of electromigration and thermomigration. A special test chip is designed for this study, in which several on-chip heater elements and temperature sensor are realized to impose and measure a temperature gradient, respectively. Our experimental results show that the electromigration lifetimes are much shorter in the presence of a temperature gradient than in a uniform temperature. The shortening of the electromigration lifetimes can be attributed to the effect of temperature gradient on electromigration-induced failure, rather than an additional driving force by thermomigration (due to a temperature gradient). Our observation is in qualitative agreement with recent theoretical model.