The development of big data and artificial intelligence technology is increasing the need for electronic devices to become smaller, cheaper, and more energy efficient, while also having enhanced functionalities. However, the miniaturization of silicon chip technology is approaching its Moore's law (i.e., physical) limits. Thus, the application of three-dimensional integrated circuits (3D ICs), in which multiple chips are stacked vertically, provides the most achievable approach for the advancement of post-Moore electronics. In the recent decade, various key techniques have been developed for stacking chips vertically such as through-silicon vias, micro-bumps, low melting point tin–bismuth solders, redistribution layers, and copper-to-copper direct bonding. However, the need for high current densities in these structures results in severe Joule heating, making electromigration (EM) an increasingly challenging problem. This paper reviews studies on EM failures, mechanisms, and potential solutions for the key components of 3D IC packaging.

Spherical (sample A), chain-like (sample B), and flake-like (sample C) cobalt powders are synthesized on a large scale through simple chemical liquid reduction method. Based on uniformly dispersing samples into a paraffin matrix, morphology-dependent electromagnetic responses in GHz range, including permittivity and permeability, are investigated for these three cobalt powders in the microwave frequency of 2-18 GHz. The calculated reflection loss (RL) indicates as-prepared samples have potential application as a candidate for microwave absorption. The maximum RL of sample A is −15.28 dB at 12.85 GHz with a matching thickness of 2.5 mm. The maximum RL of sample B is −28.05 dB at 5.74 GHz corresponding to a thickness of 2.0 mm, and the maximum RL of sample C is −41.17 dB at 5.10 GHz with a thickness of 2.5 mm. Mechanism of morphology-dependent electromagnetic response and microwave absorption of the Cobalt powders is also discussed in this paper.

We successfully achieved low-temperature assembly by reflowing the 13.5Sn-37.5Bi-45In-4Pb quaternary eutectic solder paste and the SAC 305 solder ball together at 140 °C for 5 min. The wetting angle of the mixed solder joint is 17.55°. The overall atomic percent of Pb in the mixed solder joint is less than 1%, which can be further reduced or eliminated. Moreover, after aging at 80 °C for 25 days, we observed no obvious decrease in shear strength of the fully mixed solder joint, which is the most advantage of this assembly technique over Sn58Bi solder assembly. The Bi phase segregation at the interface is slowed down compared with Sn-Bi solder joint. This low-temperature assembly is promising to be applied in advanced packaging technology to replace the eutectic Sn-Bi solder.