Cu/SAC405/Cu solder joints were fabricated using a modified reflow-soldering procedure. The samples were first maintained at 260°C for 320s, following the conventional reflow-soldering methodology. ...The reflow process was then interrupted and the samples were exposed to ultrasonic waves (USW) while they were cooling in air. Compared with a sample reflow-soldered conventionally, the solidification of the Sn–Ag0.04–Cu0.005 (SAC405) solder filler metal alloy under the influence of USW resulted in significant changes to the microstructure of the solder joints. The thickness of the Cu6Sn5 intermetallic layer at the Cu/SAC interface of the USW-solidified soldered joint decreased by as much as 76%. The β-Sn dendrite width was also reduced by as much as 67%, and the SAC matrix was filled with bundles of acicular Cu6Sn5 crystals. The formation of Ag3Sn plates was also prevented, and the size of the rod-like SAC ternary eutectic matrix was reduced from 700nm to 50nm. This behaviour is attributed to the effect of cavitation and liquid metal streaming induced by the USW on nucleation and the whole solidification process. The presence of Cu6Sn5 bundles and the refined eutectic and β-Sn dendrites in the matrix led to an average improvement in the hardness of the solder bulk by 45%.
The thermal stability of Cu/W nano-multilayers in the temperature range of 400 °C– 800 °C has been investigated by high-resolution scanning electron microcopy, X-ray photoelectron spectroscopy and ...X-ray diffraction. A repetition of 100 alternating nanolayers of Cu and W with individual thicknesses of 5 nm were prepared by magnetron sputter deposition on an α-Al2O3 substrate. In the as-deposited state, the nano-multilayers exhibit pronounced Cu and W textures with a Cu{111}<101¯>||W{110}<001¯> orientation relationship. Annealing at T ≥ 500 °C results in the appearance of a high number of line-shaped protrusions on the outer surface, which are composed of facetted Cu particles. Annealing at T ≥ 700 °C leads to a gradual degradation of the initial layered structure towards a spheroidized nanocomposite consisting of globular W particles embedded in a Cu matrix (after annealing at 800 °C). An average activation energy of 257 ± 21 kJ/mol (2.66 ± 0.22 eV) related to this degradation process is determined by in-situ high-temperature X-ray diffraction. The experimentally obtained activation energy indicates that the morphological transformation is governed by the diffusion of W along internal interfaces such as Cu/W interphase boundaries and W/W grain boundaries.
Display omitted
Anodically bonded glass/titanium and glass/steel were investigated for applications in a variety of industrial sectors. Residual stresses that build up during the bonding or cooling down of a joint ...to room temperature represent the main challenge to the joining process since they drastically weaken the mechanical strength of the joint. A layer of liquid tin-based solder in between the glass and metal part of the joint is used to reduce the internal stresses and improve the contact between the surfaces. The microstructural characterization of glass/solder/titanium and glass/solder/steel joints formed from Ni coated metal substrates indicated that Ni3Sn4 was formed for both types of joint but with a different morphology and location depending on the type of metal substrate. The average shear strength of the joints was 24MPa for glass–titanium and 21MPa for glass–steel joints. For both types of joint, the fracture crack propagated along the glass–solder interface.
Display omitted
•The average stress is not representative of the real stress state in nano-multilayer.•Strain depth profiles are derived and can be tailored by the Cu/W bilayers position.•Design of ...the bilayer blocks arrangement is a tool to tailor the Cu surface outflow.•In homogeneous nanocomposites are formed by thermal degradation of graded multilayers.
The properties and thermal stability of thin films and nano-multilayers (NMLs) are generally governed by the in-depth stress (strain) gradients rather than the average stress state. The effect of strain gradient variation in Cu/W NMLs on the thermal stability between 400 and 800 °C was investigated. The strain distribution in the NML stacks was varied by combining Cu/W bilayers with different Cu and W thicknesses of either 3 or 10 nm. A recently developed method based on in-plane grazing X-ray diffraction was adopted to extract the strain depth profiles. In addition, the evolution of the average stress in the Cu/W NMLs during growth was monitored by an in-situ wafer curvature technique. The mean residual stresses in Cu and W were found to be independent of the disposition of the different Cu/W bilayer substacks. On the contrary, the strain depth profile of the W nanolayers was found to strongly depend on the disposition of Cu/W bilayer substacks in the Cu/W NML, which resulted in different Cu outflow characteristics upon annealing. Moreover, application of different Cu/W bilayer units within the NML stack also provides an innovative pathway for producing Cu/W nanocomposites with graded thermal and mechanical properties.
In this study, the evolution of the interfacial microstructure, hardness distribution, and the joint strength of vacuum brazed commercially pure titanium were evaluated. A thin nickel layer, with ...different thicknesses, was deposited by PVD technique to serve as the brazing filler metal. Test joints were processed at temperatures of 910°C and 960°C using a soaking time of 15 and 90min. The experimental results showed that sound joints with a good wetting quality as well as lack of pores and cracks can be achieved at a brazing temperature of 960°C. A Ti2Ni intermetallic compound was formed at the interfacial area at a soaking time of 15min and with a deposition rate of 90AH which was detrimental to the joint mechanical properties. Meanwhile, at a soaking time of 90min, intermetallic compound was not detected and the diffusion of nickel was completed at all deposition rates which improve the shear strength of the joints.
Active metal brazing is a widely used technique for joining of advanced ceramics to metals. Two Ti-activated brazes have been investigated for joining of a Si3N4/TiN ceramic composite to steel. A ...commercially available braze CB6 (Ag 98.4%, In 1%, Ti 0.6% from Degussa) has been compared with a CuSnTiZr alloy. In addition, the properties of a two-layered brazing filler system with and without WC particle reinforcement have been investigated. In the present study, standard 4-point flexural strength testing of brazed joints is combined with a detailed fractographic study to determine the causes of failure in the different systems. In the best systems, an average bending strength of 466 MPa was achieved when joining ceramic to ceramic and 398 MPa when joining ceramic to metal.
Abstract In this study, we have investigated the feasibility of localized, focused ion beam (FIB)-stimulated Cu outflow in Cu/W nanomultilayers (NMLs) for manufacturing of heterogeneous ...micro-/nanojoints. Sub-micron-sized trenches were created on the nanomultilayer surface prior to heat treatment with the aim of directing the diffusion of Cu to locally defined NML surface regions. Cu outflow was triggered by annealing at 500 °C in a reducing atmosphere and lead to formation of (sub-)micron-sized Cu particles that are firmly joined to the W-terminated Cu/W NML. The results show that not only the depth of trenches (i.e., the parameters of the FIB treatment), but also the stress and the microstructure of the NMLs influence the Cu directional transport. The Cu outflow was found to be much more pronounced when the multilayer has a disordered microstructure with pores and open grain boundaries, as observed for NMLs with a tensile stress. We have thus demonstrated that FIB surface patterning enables the localized generation of (sub-)micron-sized Cu particles that can be used for manufacturing of micro-/nanojoints.
This paper gives an historic perspective of the concept of “Interfacial Design” in joined (e.g. soldered, brazed, diffusion bonded) assemblies. During the course of history, the awareness grew that ...the interface in a material joint can be perceived at different length scales. With the continuing development of joining materials and technologies, it became evident that the performance of assemblies is critically dependent on the structure and composition of the multiple internal interfaces in the material joints. Resulting trends in the microstructural design of soldering, brazing, and other bonding materials by smart engineering of internal interfaces, as driven by increasingly complex technological requirements, are briefly addressed.
PDF
