A technique has been developed to facilitate analysis of the microstructural evolution of solder bumps after current stressing. Eutectic SnPb solders were connected to under-bump metallization (UBM) of Ti/Cr-Cu/Cu and pad metallization of Cu/Ni/Au. It was found that the Cu6Sn5 compounds on the cathode/chip side dissolved after the current stressing by 5 × 103 A/cm2 at 150 °C for 218 h. However, on the anode/chip side, they were transformed into (Nix,Cu1-x)3Sn4 in the center region of the UBM, and they were converted into (Cuy,Ni1-y)6Sn5 on the periphery of the UBM. For both cathode/substrate and anode/substrate ends, (Cuy,Ni1-y)6Sn5 compounds were transformed into (Nix,Cu1-x)3Sn4. In addition, the bumps failed at cathode/chip end due to serious damage of the UBM and the Al pad. A failure mechanism induced by electromigration is proposed in this paper.

No abstract

In this work, contact angle, spreading area, and isothermal aging tests were conducted to study the difference between Sn-3Ag-0.5Cu lead-free solder and its composite solder at different multiwalled carbon nanotube reinforcement volume fractions. The material interaction between the solder and the substrate at different aging temperatures and times was investigated using scanning electron microscopy elemental analysis. The experimental results indicated that the composite solder had a lower contact angle as well as good spreading area. An intermetallic compound layer was found between the solder and the copper substrate, and the thickness of this reaction layer increased with increasing aging temperature and time. Meanwhile, the intermetallic compound layer of multiwalled carbon nanotube reinforcement composite solder was thicker than that of the Sn-3Ag-0.5Cu lead-free solder. The composite solder with 0.1 vol% multiwalled carbon nanotube reinforcement addition exhibited better comprehensive properties than composite solders with other reinforcement volume fractions.

No abstract

The main objective of the present work was to establish a friction-stir-welding process to weld dissimilar metal joints on AA6082 and AA6066 aluminum alloy plates. Joints were made while varying tool rotation speed at a constant traveling speed and at the same time adding oxygen-free copper reinforcement inside the weld nugget for the purpose of analyzing the microstructural evolution and mechanical properties of the joint. Results showed that the morphology of the microstructure in the weld nugget changed significantly with rotation speed. Optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy analyses revealed that oxygen-free copper particles could be uniformly dispersed into the weld nugget because of higher rotation speeds. Because of the presence of reinforcement particles homogenously distributed inside the nugget zone, the mechanical properties, such as ultimate tensile strength and hardness of weld joint, were greatly improved.