Formation of TiC via interface reaction between diamond grits and Sn-Ti alloys at relatively low temperatures

In this paper, interfacial reaction between diamond grit and Sn-6Ti alloy was systematically studied at brazing temperatures from 600 to 1030 °C. A thin and uniform layer of scallop-like nano-sized TiC grains was formed after brazing for 30 min at 600 °C, and interfacial TiC grains subsequently coarsened as brazing temperature increased to 740 and 880 °C. Strip-like columnar TiC grains in a bilayer structure was further grown as brazing temperature increased to 930 °C. After brazing at 1030 °C, a dense layer of columnar TiC grains were formed. Based on the TEM micrographs of interfacial TiC, the formation and evolution of the growth morphologies of interfacial TiC was believed to be controlled by the diffusion of C flux from diamond grits, which is dependent on the brazing temperatures

The influence of ageing on the stabilisation of interfacial (Cu,Ni)6(Sn,Zn)5 and (Cu,Au,Ni)6Sn5 intermetallics in Pb-free Ball Grid Array (BGA) solder joints

Formation/growth behaviour, phase stability, and mechanical properties of interfacial CuSn intermetallics influenced by micro-alloying in Pb-free solder joints, are of ongoing interest as this phase is crucial to the service reliability of solder joints. Our recent work has demonstrated that, after reflow, the homogeneously located micro-alloying elements of both Ni and Zn in interfacial (Cu,Ni)(Sn,Zn) act to increase phase stability and prevent the undesirable polymorphic phase transformation of CuSn. This paper further investigates the influence of ageing on the phase stability of interfacial intermetallics containing Ni, Zn and Au. Phase transformations of hexagonal to monoclinic CuSn driven by ageing, was suppressed by alloying Ni/Zn/Au, resulting in improvements in phase stability. The findings help to further understand the reliability of interfacial structures in micro-alloyed Pb-free solder joints

Reliability and availability analysis of a multistate repairable system with dependent deteriorations and redundancy

Maintenance management is to design, operate, and maintain the reliability and availability of assets at a required performance level using the lowest possible cost. The standby redundancy is one of the means to achieve highly reliable system with less dependable units. As commonly used performance indicator, the reliability and availability should be precisely analysed for a repairable standby system. The reliability of a standby system is mainly studied in the framework of lifetime approach. Most existing models are developed for a two-unit standby system and a Kout- of-N system with identical units. The system units are assumed to be binary-state and the failures of system units are modelled as sudden failures. The deteriorations of units are modelled as time-dependent failure rate and are assumed to be independent. In addition, most of the existing models do not consider maintenance is carried out on the system. In reality, the deteriorations and the resultant failures in real-world systems are often interactive with each other. The systems normally experience several, often imperfect, restorations before a complete renewal. Therefore, the study of different repair policies, such as opportunistic and individual policies, in multi-unit systems need also be investigated. To address the problem, the reliability and availability models for a 2-out-of-3 cold standby system will be studied in a multi-state system reliability framework. A multistate multi-path failure mode is proposed to model the interactive deteriorations. The concept of repair matrix will be adopted to model the effect of unit level restorations on system reliability. The availabilities under individual repair policy and opportunistic repair policy will be developed

Deformation and removal of semiconductor and laser single crystals at extremely small scales

Semiconductor and laser single crystals are usually brittle and hard, which need to be ground to have satisfactory surface integrity and dimensional precision prior to their applications. Improvement of the surface integrity of a ground crystal can shorten the time of a subsequent polishing process, thus reducing the manufacturing cost. The development of cost-effective grinding technologies for those crystals requires an in-depth understanding of their deformation and removal mechanisms. As a result, a great deal of research efforts were directed towards studying this topic in the past two or three decades. In this review, we aimed to summarize the deformation and removal characteristics of representative semiconductor and laser single crystals in accordance with the scale of mechanical loading, especially at extremely small scales. Their removal mechanisms were critically examined based on the evidence obtained from high-resolution TEM analyses. The relationships between machining conditions and removal behaviors were discussed to provide a guidance for further advancing of the grinding technologies for those crystals

Growth orientations and mechanical properties of Cu6Sn5 and (Cu,Ni)6Sn5 on poly-crystalline Cu

Lead-free solders are important materials in current generation electrical packages, due to the increasingly stringent legislative requirement aimed at reducing the use of lead. The lead-free solders based on the Sn-Cu system with Ni addition have become popular because of their superior soldering properties, as well as their comparatively low cost. This research investigates the effect of Ni addition on the growth morphologies, crystal orientations and mechanical properties of Cu Sn at the interface between hyper-eutectic Sn-Cu high-temperature lead-free solder alloys and Cu substrates, prior to and after aging, by the use of X-ray diffraction (XRD), scanning electron microscopy (SEM) and nanoindentation. The (Cu,Ni) Sn in Sn-Cu-Ni/Cu solder joints showed a more strongly oriented (1 0 1) texture, compared to the Cu Sn in Sn-Cu/Cu solder joints. The Ni-induced (1 0 1) texture contributes to higher and more scattered average values with larger standard deviations in both elastic modulus and hardness for (Cu,Ni) Sn

Influence of sintering temperature on dicing performances of metal-bonded diamond blades on sapphire

A novel Ti–Al-Diamond metal matrix composite (MMC) material has been recently developed for fabricating diamond blade that is an indispensable tool for the mechanical dicing of optoelectronic devices. This work aims to achieve a deep understanding of the influence of sintering temperature on the microstructure, the mechanical and frictional properties, and the grinding and dicing performances on hard-and-brittle materials. Firstly, the microstructures and the mechanical and frictional properties of Ti–15Al-25 vol% Diamond metal matrix composites (MMCs) sintered at 750, 850, and 950 °C were investigated. The upraising of sintering temperature results in the enhancement of the diffusion between constitute elements, which consequently increases the hardness and bending strength, but reduces the porosity of sintered MMCs. Then, Ti–15Al-25 vol% Diamond blades were sintered at 750, 850, and 950 °C for dicing of sapphire. The increase in sintering temperature was found to be responsible for the compromise of the self-sharpness capability of diamond blades, resulting in an inferior dicing quality in terms of the chipping size, the kerf width, and the surface roughness, but an improved dicing ratio. Results obtained in this work indicate that sufficient porosity and self-sharpening capability play the most determinant role in satisfying the dicing quality of sapphire

Microstructure and Bonding Strength of Low-Temperature Sintered Ag/Nano-Ag Films/Ag Joints

Nano-Ag paste is one of the most widely used die-attachment materials in modern electronic devices, which are gaining continuously increasing application in transportation industries. The nano-Ag film in a pre-formed dimension and free from the use of chemical dispersing agents has been proposed to be a promising alternative to nano-Ag paste for the die-attachment application. Although the bonding mechanisms of Nano-Ag paste have been extensively studied, little is known about the relationship between the microstructure and mechanical properties of low-temperature-sintered Ag/nano-Ag film/Ag joints. In this work, the influences of temperature, pressure, and dwell time at peak temperature on the microstructure and the shear strength of low-temperature-sintered Ag/nano-Ag film/Ag joints were systematically investigated. Mechanical properties tests indicate that both temperature and pressure have pronounced effects on the bonding strength of sintered Ag/nano-Ag film/Ag joints. TEM and hot nanoindentation characterizations further reveal that the sintering temperature plays the most determinant role in the coarsening of nano-Ag film and, hence, the bonding and fracture behaviors of Ag/nano-Ag film/Ag joints sintered at 210–290 °C. The diffusion-induced coarsening of nano-Ag particles can be activated, but remains sluggish at 250 °C, and the mechanical integrity of sintered joints is circumscribed by the interfacial bonding between nano-Ag film and Ag substrate after sintering at 290 °C

Thermal expansion of Cu6Sn5 and (Cu,Ni)(6)Sn-5

CuSn is a common intermetallic compound formed during electrical packaging. It has an allotropic transformation from the low-temperature monoclinic η′-CuSn to high-temperature hexagonal η-CuSn at equilibrium temperature 186 °C. In this research, the effects of this allotropic transformation and Ni addition on the thermal expansion of η′- and/or η-CuSn were characterized using synchrotron x-ray diffraction and dilatometry. A volume expansion during the monoclinic to hexagonal transformation was found. The addition of Ni was found to decrease the undesirable thermal expansion by stabilizing the hexagonal Cu Sn at temperatures below 186 °C and reducing the overall thermal expansion of CuSn