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Soldier boy
Follows Ricky from 1987-1991, and Samuel in 2006, as they are abducted to serve as child-soldiers in Joseph Kony's Lord's Resistance Army in Uganda. Includes historical notes and information about Friends of Orphans, an organization founded by Ricky Richard Anywar, on whose life the story is partly based.
Book
Effect of Ce on the microstructure and property of Sn0.7Cu solder
The effect of Ce multi-addition on wettability and microstructure of Sn-0.7Cu solder was investigated. The results indicated that the multi-addition of Ce could greatly improve the wettability of solder and refine the microstructure of solder matrix. The optimal property of solder was obtained when the addition of Ce reached 0.1 wt.%. With the increasing of Ce addition, black phase appeared and tend to be accumulated in the solder matrix. EDS results indicated that the composition of black phase contained varies elements including Sn, Cu, Ni, and Ce. Compared with the previous research results of solder with excessive Ce addition, no obviously Sn-Nd phase was observed while a small amount of Ga2Nd phase appeared in the solder matrix.
Journal Article
Systematic Study of Liquid-State Interfacial Reactions Between Co and In-Sn Solders with Varying Sn Contents
This study investigated the interfacial reactions between Co and In-Sn solders, with various compositions, up to 90 at% Sn, at 350°C, with the aim of evaluating their potential for use in the solid–liquid interdiffusion (SLID) process. The results demonstrated that the reaction phases formed at the interfaces exhibited significant variations depending on the Sn content present in the In-Sn solders. For Sn content below 2 at%, the reaction phase was CoIn
3
. Notably, the CoIn
3
in the In-2 at% Sn/Co reaction exhibited a linear growth at a rate of ~ 15
μ
m/h, which was significantly higher compared to the In/Co reaction. The accelerated growth rate could be attributed to the minor addition of Sn, which facilitated both the nucleation and growth of CoIn
3
. With an increase in Sn content to 2.5–3.5 at%, the dominant reaction phase shifted to Co(In,Sn)
2
, but its growth was significantly hindered. With a further increase in Sn content within the range of 4–35 at%, the irregular Co(Sn,In) phase became dominant. However, as the Sn content exceeded 36 at% and extended up to 90 at%, the Co(Sn,In)
2
phase remained stable at the interface, and its growth decreased significantly with increasing Sn content. The observed shift in the reaction phases is closely related to the local phase equilibrium. The suggested phase diagram of Co-In-Sn system was proposed to further understand the relationship between interfacial reaction and phase equilibrium. The Sn content of In-Sn solders not only influenced the formed reaction phase but also the growth rates and microstructures. Careful control of Sn content is crucial for the SLID process of In-Sn/Co system.
Journal Article
Effect of Ni, Zn, Au, Sb and In on the Suppression of the Cu3Sn Phase in Sn-10 wt.%Cu Alloys
Since manufacturing is transitioning into Pb-free solder development for electronic assembly and packaging, consumer demands for more compact electronics have increased the importance of reliability issues brought about by the increased density of circuitry. Therefore, the role of alloying elements that can be added to common Pb-free solders such as Sn-Cu or Sn-Ag-Cu alloys in enhancing the properties and performance of the solder becomes important. Microstructural analysis along with direct observation in situ synchrotron radiography were used to study the effect of Ni, Zn, Au, In and Sb on the development of phases in Sn-10 wt.%Cu (Sn-10Cu). It was found that adding Ni and Zn to a Sn-10Cu alloy had the greatest impact on the microstructure with the Cu
3
Sn phase completely absent after these additions were made. Additions of Au and In also resulted in a reduction in the amount of Cu
3
Sn; however, the effect was not as pronounced. Removing the Cu
3
Sn phase from Sn-Cu Pb-free solder alloys is a possible approach for the design of more desirable microstructures that translate to better performance in modern electronic packaging.
Journal Article
Influence of Flux and Related Factors on Intermetallic Layer Growth within SAC305 Solder Joints
Flux contained in solder paste significantly affects the process of solder joint creation during reflow soldering, including the creation of an intermetallic layer (IML). This work investigates the dependence of intermetallic layer thickness on ROL0/ROL1 flux classification, glossy or matt solder mask, and OSP/HASL/ENIG soldering pad surface finish. Two original SAC305 solder pastes differing only in the used flux were chosen for the experiment. The influence of multiple reflows was also observed. The intermetallic layer thicknesses were obtained by the image analysis of micro-section images. The flux type proved to have a significant impact on the intermetallic layer thickness. The solder paste with ROL1 caused an increase in IML thickness by up to 40% in comparison to an identical paste with ROL0 flux. Furthermore, doubling the roughness of the solder mask has increased the resulting IML thickness by 37% at HASL surface finish and by an average of 22%.
Journal Article
Effects of solder thickness on interface behavior and nanoindentation characteristics in Cu/Sn/Cu microbumps
The thickness of the solder, for Cu/Sn/Cu microbumps with dimensions of tens of microns or even a few microns (such as 40 µm, 15 µm, 10 µm, and 6 µm), can have a significant effect on the interfacial transfer and the performance. During the reflow stage, it was found that the grains of Cu6Sn5 showed “staggered growth” phenomenon in some areas of the microbumps with the solder thickness of 6 µm and the thickness of intermetallic compounds’ (IMCs) layer grew the fastest; that the second fastest growth of 40 µm; that the third fastest growth of 15 µm, and that the slowest growth of 10 µm. After thermal aging at 160 °C for 80 h, the thickness of the IMC layer in descending order was the microbumps with the solder thickness of 15 µm, 10 µm, 40 µm, and 6 µm. These results were caused by the difference in the element concentration. In addition, there were four main components in the microbumps: Cu, Sn, Cu6Sn5, and Cu3Sn. The hardness of Cu and Sn was about 1.37 ± 0.3 Gpa and 0.13 ± 0.03 Gpa, respectively. And the hardness of Cu6Sn5 and Cu3Sn was about 6.7 ± 0.3 Gpa and 6.2 ± 0.4 Gpa, respectively. The nanoindentation hardness analysis showed a general increase in the hardness of the microbumps after thermal aging for 80 h, compared with that after reflow. And the thinner the solder thickness was, the more obvious the hardness improvement was.
Journal Article
Thermal Fatigue Failure of Micro-Solder Joints in Electronic Packaging Devices: A Review
In electronic packaging products in the service process, the solder joints experience thermal fatigue due to temperature cycles, which have a significant influence on the performance of electronic products and the reliability of solder joints. In this paper, the thermal fatigue failure mechanism of solder joints in microelectronic packages, the microstructure changes of the thermal fatigue process, the influence factors on the joint fatigue life, and the simulation analysis and forecasting of thermal fatigue life are reviewed. The results show that the solder joints are heterogeneously coarsened, and this leads to fatigue cracks occurring under the elevated high-temperature phase of alternating temperature cycles. However, the thickness of the solder and the hold time in the high-temperature phase do not significantly influence the thermal fatigue. The coarsened region and the IMC layer thicken with the number of cycles, and the cracks initiate and propagate along the interface between the intermetallic compound (IMC) layer and coarsened region, eventually leading to solder joint failure. For lead-containing and lead-free solders, the lead-containing solder shows a faster fatigue crack growth rate and propagates by transgranular mode. Temperature and frequency affect the thermal fatigue life of solder joints to different degrees, and the fatigue lifetime of solder joints can be predicted through a variety of methods and simulated crack trajectories, but also through the use of a unified constitutive model and finite element analysis for prediction.
Journal Article
Effect of Isothermal Annealing on Sn Whisker Growth Behavior of Sn0.7Cu0.05Ni Solder Joint
This paper presents an assessment of the effect of isothermal annealing of Sn whisker growth behavior on the surface of Sn0.7Cu0.05Ni solder joints using the hot-dip soldering technique. Sn0.7Cu and Sn0.7Cu0.05Ni solder joints with a similar solder coating thickness was aged up to 600 h in room temperature and annealed under 50 °C and 105 °C conditions. Through the observations, the significant outcome was the suppressing effect of Sn0.7Cu0.05Ni on Sn whisker growth in terms of density and length reduction. The fast atomic diffusion of isothermal annealing consequently reduced the stress gradient of Sn whisker growth on the Sn0.7Cu0.05Ni solder joint. It was also established that the smaller (Cu,Ni)6Sn5 grain size and stability characteristic of hexagonal η-Cu6Sn5 considerably contribute to the residual stress diminished in the (Cu,Ni)6Sn5 IMC interfacial layer and are able to suppress the growth of Sn whiskers on the Sn0.7Cu0.05Ni solder joint. The findings of this study provide environmental acceptance with the aim of suppressing Sn whisker growth and upsurging the reliability of the Sn0.7Cu0.05Ni solder joint at the electronic-device-operation temperature.
Journal Article
Effects of Reflow Profile and Miniaturisation on the Integrity of Solder Joints in Surface Mount Chip Resistors
The integrity of solder joints of components in an electronic device is critical to the device reliability. The miniaturisation trend in the development of electronic products has continued to challenge the shear strength of the solder joints in these devices and necessitates implementation of optimal reflow profiles to achieve maximum joint strength. This study proposes an optimal parameter combination of reflow profile factors which demonstrate potential for delivering maximum shear strength of solder joints. The Taguchi design of experiment (DoE) is employed to generate eight orthogonal array designs of L24 reflow profiles. The factors/parameters investigated are preheat gradient, time above liquidus (TAL), peak temperature and cooling rate. Three test vehicles of varying solder joint sizes are made from R1206, R0805 and R0603 resistors. Reflow profile number 3 constituting 1.2°C/s preheat, 45 s TAL, 245°C peak temperature and 60% cooling rate is optimal because it yielded joints with the highest strength and ca. 4 µm intermetallic compound thickness. The solder joint shear strength decreased with a decrease in the size of the lead-free joint irrespective of the reflow profile implemented. These results will be useful for electronic packaging and reliability engineers faced with challenges of improving device operational mechanical performance in the continuing trend of product miniaturisation.
Journal Article
Thermomigration Microstructure and Properties of Ni Nanoparticle-Reinforced Sn58Bi Composite Solder/Cu Solder Joint
A Sn58Bi composite solder reinforced by Ni nanoparticles was prepared using a mechanical mixing technique, and the thermomigration microstructure and properties of the solder joints were studied. The findings indicate that incorporating an appropriate quantity of Ni nanoparticles can enhance the microstructure of the composite solder and mitigate the coarsening of Bi-phase segregation. At 0.75 weight percent Ni nanoparticle content, the composite solder’s tensile strength is 59.7 MPa and its elongation is 54.6%, both of which are noticeably greater than those of the base solder. When the thermal loading time is 576 h, the shear strength of the composite solder joint is 25.5 MPa, which is 30.1% higher than that of the base solder joint. This study reveals that the shear fracture path shifts from the boundary region between the solder seam and the IMC layer to the IMC layer itself. Concurrently, the fracture mode evolves from a mix of brittle–ductile fracture, characterized by quasi-cleavage, to a predominantly brittle fracture, marked by numerous “rock candy-like” cross-sectional features and secondary cracking. Adding Ni nanoparticles to the Sn58Bi composite solder/Cu solder junction can significantly extend its service life.
Journal Article