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Based on the size effect on solidification behavior of lead-free solders, we propose a novel method to prepare solder joints with the metallurgical bonding between the undercooled liquid solder and Cu metallization under the temperature lower than the solder's melting point. The interfacial reaction and growth behavior of intermetallic compound (IMC) between the undercooled liquid Sn-3.0Ag-0.5Cu solder...
The solder joint's volume and interfacial reaction during the soldering significantly affect its solidification behavior and microstructure feature; further, the microstructure of the solder matrix and the intermetallic compounds (IMC) have a direct impact on the performance and reliability of the solder joint. In this study, the effects of the solder volume and interfacial reaction on the undercooling...
The fracture behavior of microscale lead-free Sn-3.0Ag-0.5Cu solder joints under electrotensile load was characterized, in comparison with those under pure tensile load. Experimental results show that under electrotensile load the stress-strain and strain-time curves of joints exhibit three distinct stages, i.e., the fast deformation stage at the beginning of loading, linear deformation stage and...
During the soldering process, Kirkendall voids may form at the Cu/Cu3Sn interface and in Cu3Sn compound layer. Excessive formation and growth of Kirkendall voids may increase the potential for brittle interfacial fracture, and the existence of voids will reduce the thermal conductivity. Thus, characterization of formation and growth of Kirkendall voids is very important to the evaluation of performance...
The fracture behavior of microscale lead-free Sn-3.0Ag-0.5Cu solder joints under electrotensile load was characterized, in comparison with those under pure tensile load. Experimental results show that under electrotensile load the stress-strain and strain-time curves of joints exhibit three distinct stages, i.e., the fast deformation stage at the beginning of loading, linear deformation stage and...
During the soldering process, Kirkendall voids may form at the Cu/Cu3Sn interface and in Cu3Sn compound layer. Excessive formation and growth of Kirkendall voids may increase the potential for brittle interfacial fracture, and the existence of voids will reduce the thermal conductivity. Thus, characterization of formation and growth of Kirkendall voids is very important to the evaluation of performance...
The solder joint's volume and interfacial reaction during the soldering significantly affect its solidification behavior and microstructure feature; further, the microstructure of the solder matrix and the intermetallic compounds (IMC) have a direct impact on the performance and reliability of the solder joint. In this study, the effects of the solder volume and interfacial reaction on the undercooling...
The influence of the cooling rate and the type of under bump metallization (UBM, i.e., Cu and Ni) on the undercooling and solidification behavior of Sn-Ag-Cu (SAC) based solders (i.e., Sn-1.0Ag-0.5Cu, Sn-3.0Ag-0.5Cu and Sn-3.8Ag-0.7Cu) and their joints was characterized. The results show that the cooling rate has little influence on the undercooling of Sn-1.0Ag-0.5Cu and Sn-3.0Ag-0.5Cu solder balls,...
The effect of the activators and surfactants in halogen-free fluxes on the wettability of Sn-0.7Cu-0.05Ni solder on Cu substrate (or under bump metallization, UBM) was investigated in this study. The spreading area of Sn-0.7Cu-0.05Ni solder on Cu substrate was used to estimate the wetting performance of the solder influenced by the activators with different amounts added in halogen-free fluxes. The...
During soldering process employing Sn-based lead-free solders, an intermetallic compound (IMC) layer forms between the molten solder and pad/under bump metallization (UBM), whose morphology and thickness play an important role in controlling the service performance of the solder joints, in particular for solder interconnects with the decreasing size where the interfacial IMC layer takes up a high...
The influence of the pre-existing void in the Cu/Sn-58Bi/Cu solder joint on electromigration behavior was investigated by in-situ SEM observation and focused ion beam (FIB) analysis. The results show that the void with smooth internal surface has no influence on the Bi atom migration, while the one with a sharp notch may easily result in Bi atom congregation and further lead to the formation of cracks...
The rapid development of modern electronic devices and products has proposed a great demand for the continuous scaling down in the dimension of solder joints and interconnect pitches in packaging; accordingly the current density in solder interconnects gets higher and higher. The higher current density can easily result in electromigration (EM) which has been regarded as a serious reliability issue...
The microstructural evolution and mechanical behavior of line-type Ni/Sn3.0Ag0.5Cu/Ni interconnects with a small thickness (or height) of 100 µm during isothermal aging were investigated. Microstructural analysis shows that both (Ni,Cu)3Sn4 and (Cu,Ni)6Sn5 IMC phases formed at the interface of the as-reflowed joints; however, after the aging treatment at 125 °C for 100 h or more, the interfacial (Cu,Ni)...
The dimension of solder micro-interconnects has been scaling down to meet the trend of miniaturization of electronic products and devices. In this study, Cu/Sn-0.7Cu-0.05Ni (SCN)/Cu sandwich solder joints with a very small thickness (or height), in the range of 10 to 100 µm, were prepared and the size effect on the microstructure and mechanical behavior of the joints were investigated systematically...
The solidification behavior of Sn-3.0Ag-0.5Cu solders and Sn-3.0Ag-0.5Cu/Cu joints was investigated by using differential scanning calorimetry (DSC) incorporated into the reflow process. The critical factors influencing the undercooling behavior of the solders and joints, such as the solder size, composition and substrate size, were examined. The results show that the type of the primary solidification...
Thus far, there is a severe lack of understanding about interfacial fracture and impact behavior of the microscale lead-free solder interconnects. In this study, the finite element simulation and analytical method were used to characterize the interfacial fracture and impact behavior at the interfaces of the microscale Sn-Ag-Cu solder joints. The intersection of a linear microcrack tip upon Sn-Ag-Cu...
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