Perpendicular growth characteristics of Cu-Sn intermetallic compounds at the surface of Sn99Cu1/Cu solder interconnects

The growth of intermetallic compounds (IMCs) on the free surface of 99Sn-1Cu solder joints perpendicular to the interdiffusion direction has been investigated in this work. The specimens were specifically designed and polished to reveal a flat free surface at the solder/Cu interface for investigation. After aging at 175°C for progressively increased durations, the height of the perpendicular IMCs was examined and found to follow a parabolic law with aging duration that could be expressed as $y = 0.11\sqrt t$, where t is the aging duration in hours and y is the height of the perpendicular IMCs in μm. For comparison, the planar growth of IMCs along the interdiffusion direction was also investigated in 99Sn-1Cu/Cu solder joints. After prolonged aging at 175°C, the thickness of the planar interfacial IMC layers also increased parabolically with aging duration and could be expressed as $h_{\rm{IMC}} = 0.27\sqrt t + 4.6$, where h is the thickness in μm and t is the time in hours. It was found that both the planar and perpendicular growth of the IMCs were diffusion-controlled processes, but the perpendicular growth of the IMCs was much slower than their planar growth due to the longer diffusion distance. It is proposed that Cu3Sn forms prior to the formation of Cu6Sn5 in the perpendicular IMCs, being the reverse order compared with the planar IMC growth

Micro-mechanical and fracture characteristics of Cu6Sn5 and Cu3Sn intermetallic compounds under micro-cantilever bending

This study focuses on the fracture characteristics of Cu6Sn5 and Cu3Sn micro beams under micro-cantilever bending tests. These micro beams were fabricated by focused ion beam (FIB) from the Sn-rich solder joints aged at 175 °C for 1132.5 h, and then tested using a nanoindenter with a flat tip. Experimental results show that both Cu6Sn5 and Cu3Sn micro beams underwent elastic deformation before their failure. From fractographic analysis, both cleavage fracture and intergranular fracture can be identified from the tested Cu6Sn5 micro beams, while only intergranular fracture was found in Cu3Sn micro beams. Furthermore, based on the experimental results, finite element analysis was carried out to evaluate the tensile fracture strength and strain of Cu6Sn5 and Cu3Sn micro beams. For Cu6Sn, the tensile fracture strength was estimated to be 1.13 ± 0.04 Pa and the average tensile strain was 0.01. The tensile fracture strength and strain of Cu3Sn were evaluated to be 2.15 ± 0.19 GPa and 0.016, respectively

Study of height reduction of Sn99Cu1/Cu solder joints as a result of isothermal aging

Sn99Cu1/Cu solder joints were investigated after isothermal aging at 175°C for different lengths of time under vacuum conditions. The results revealed height reduction of the solder of approximately 1.2 μm after aging for 1132.5 h. This was primarily attributed to growth of a layer of interfacial intermetallic compounds. The reduction was measured by use of a copper block containing a recess filled with solder, which was reflowed then polished flat. Height reduction of the solder joint during aging was found to obey the parabolic law $\Delta h = -\!\!\hbox{ }0.031\sqrt t$, and was in excellent agreement with theoretical calculation

Evolution of the hardness and Young’s moduli of interlayers in Sn99Cu1/Cu solder joints subjected to isothermal ageing

The interlayers at solder/pad interface are critical to the reliability of solder joints; hence, their mechanical properties is of vital importance. However, the correlation between service duration and evolution of mechanical characteristics of these interlayers has seldom been reported. In this work, hardness and Young’s moduli of Cu6Sn5, Cu3Sn and Cu were evaluated by nanoindenation after ageing for every 100 h up to 500 h. It was found that hardness and Young’s moduli of Cu6Sn5 and Cu3Sn dropped with aging and reached the bottom at 200 h and 300 h, respectively, followed by a gradual increase. This U-shape curve was generally opposite to the evolution of corresponding parameters in Cu. Evolution of mechanical properties of IMCs can be attributed to constrained volume shrinkage induced by solidstate reactions that producing IMCs. The resultant stress ultimately affected load–displacement curves recorded by nanoindentation tests. The observed reverse evolution trend of examined parameters of Cu and adjacent IMC layers was a result of mutual constraint posed by Cu3Sn/Cu interface

Pyrolysis of Metal–Organic Frameworks to Fe₃O₄@Fe₅C₂ Core–Shell Nanoparticles for Fischer–Tropsch Synthesis

We prepared highly active catalysts for Fischer–Tropsch (FT) synthesis through the pyrolysis of iron-containing metal–organic frameworks (MOFs). The Fe-time yields of the nitrogen-doped catalyst were as high as 720 μmol_CO g_Fe^–1 s^–1 under the conditions of 300 °C, 2 MPa, and H₂/CO = 1, which is a value that surpasses that of most FT catalysts reported in the literature. The pyrolysis of the MOFs yielded nanoparticles with a unique iron oxide@iron carbide core–shell structure dispersed on carbon supports. Such a structure is favorable for FT synthesis and has never been reported previously. Our strategy resolved the problem that the strong metal–support interactions that are usually required to stabilize dispersed particles in calcination compromise the catalytic activity, because of the difficulty of reducing metal oxides. Moreover, we found full coverage of carbonates on the particle surfaces, which likely result from decarboxylation of the MOFs and further stabilize the particles before decomposing to CO₂, leaving an active surface rich with dangling bonds for catalytic turnover

Confinement of Ultrasmall Cu/ZnO_<i>x</i> Nanoparticles in Metal–Organic Frameworks for Selective Methanol Synthesis from Catalytic Hydrogenation of CO₂

The interfaces of Cu/ZnO and Cu/ZrO₂ play vital roles in the hydrogenation of CO₂ to methanol by these composite catalysts. Surface structural reorganization and particle growth during catalysis deleteriously reduce these active interfaces, diminishing both catalytic activities and MeOH selectivities. Here we report the use of preassembled bpy and Zr₆(μ₃-O)₄(μ₃-OH)₄ sites in UiO-bpy metal–organic frameworks (MOFs) to anchor ultrasmall Cu/ZnO_<i>x</i> nanoparticles, thus preventing the agglomeration of Cu NPs and phase separation between Cu and ZnO_<i>x</i> in MOF-cavity-confined Cu/ZnO_<i>x</i> nanoparticles. The resultant Cu/ZnO_<i>x</i>@MOF catalysts show very high activity with a space–time yield of up to 2.59 g_MeOH kg_Cu^–1 h^–1, 100% selectivity for CO₂ hydrogenation to methanol, and high stability over 100 h. These new types of strong metal–support interactions between metallic nanoparticles and organic chelates/metal-oxo clusters offer new opportunities in fine-tuning catalytic activities and selectivities of metal nanoparticles@MOFs

Metal–Organic Frameworks Stabilize Mono(phosphine)–Metal Complexes for Broad-Scope Catalytic Reactions

Mono­(phosphine)–M (M–PR₃; M = Rh and Ir) complexes selectively prepared by postsynthetic metalation of a porous triarylphosphine-based metal–organic framework (MOF) exhibited excellent activity in the hydrosilylation of ketones and alkenes, the hydrogenation of alkenes, and the C–H borylation of arenes. The recyclable and reusable MOF catalysts significantly outperformed their homogeneous counterparts, presumably via stabilizing M–PR₃ intermediates by preventing deleterious disproportionation reactions/ligand exchanges in the catalytic cycles

Multimetal-Based Metal–Organic Framework System for the Sensitive Detection of Heart-Type Fatty Acid Binding Protein in Electrochemiluminescence Immunoassay

In this work, an electrochemiluminescence (ECL) quenching system using multimetal–organic frameworks (MMOFs) was proposed for the sensitive and specific detection of heart-type fatty acid-binding protein (H-FABP), a marker of acute myocardial infarction (AMI). Bimetallic MOFs containing Ru and Mn as metal centers were synthesized via a one-step hydrothermal method, yielding RuMn MOFs as the ECL emitter. The RuMn MOFs not only possessed the strong ECL performance of Ru(bpy)32+ but also maintained high porosity and original metal active sites characteristic of MOFs. Moreover, under the synergistic effect of MOFs and Ru(bpy)32+, RuMn MOFs have more efficient and stable ECL emission. The trimetal-based MOF (FePtRh MOF) was used as the ECL quencher because of the electron transfer between FePtRh MOFs and RuMn MOFs. In addition, active intramolecular electron transfer from Pt to Fe or Rh atoms also occurred in FePtRh MOFs, which could promote intermolecular electron transfer and improve electron transfer efficiency to enhance the quenching efficiency. The proposed ECL immunosensor demonstrated a wide dynamic range and a low detection limit of 0.01–100 ng mL–1 and 6.8 pg mL–1, respectively, under optimal conditions. The ECL quenching system also presented good specificity, stability, and reproducibility. Therefore, an alternative method for H-FABP detection in clinical diagnosis was provided by this study, highlighting the potential of MMOFs in advancing ECL technology

Warm-White-Light-Emitting Diode Based on a Dye-Loaded Metal–Organic Framework for Fast White-Light Communication

A dye@metal–organic framework (MOF) hybrid was used as a fluorophore in a white-light-emitting diode (WLED) for fast visible-light communication (VLC). The white light was generated from a combination of blue emission of the 9,10-dibenzoate anthracene (DBA) linkers and yellow emission of the encapsulated Rhodamine B molecules. The MOF structure not only prevents dye molecules from aggregation-induced quenching but also efficiently transfers energy to the dye for dual emission. This light-emitting material shows emission lifetimes of 1.8 and 5.3 ns for the blue and yellow components, respectively, which are significantly shorter than the 200 ns lifetime of Y₃Al₅O₁₂:Ce³⁺ in commercial WLEDs. The MOF-WLED device exhibited a modulating frequency of 3.6 MHz for VLC, six times that of commercial WLEDs

Förster Energy Transport in Metal–Organic Frameworks Is Beyond Step-by-Step Hopping

Metal–organic frameworks (MOFs) with light-harvesting building blocks designed to mimic photosynthetic chromophore arrays in green plants provide an excellent platform to study exciton transport in networks with well-defined structures. A step-by-step exciton random hopping model made of the elementary steps of energy transfer between only the nearest neighbors is usually used to describe the transport dynamics. Although such a nearest neighbor approximation is valid in describing the energy transfer of triplet states via the Dexter mechanism, we found it inadequate in evaluating singlet exciton migration that occurs through the Förster mechanism, which involves one-step jumping over longer distance. We measured migration rates of singlet excitons on two MOFs constructed from truxene-derived ligands and zinc nodes, by monitoring energy transfer from the MOF skeleton to a coumarin probe in the MOF cavity. The diffusivities of the excitons on the frameworks were determined to be 1.8 × 10^–2 cm²/s and 2.3 × 10^–2 cm²/s, corresponding to migration distances of 43 and 48 nm within their lifetimes, respectively. “Through space” energy-jumping beyond nearest neighbor accounts for up to 67% of the energy transfer rates. This finding presents a new perspective in the design and understanding of highly efficient energy transport networks for singlet excited states