Applications of multi-walled carbon nanotube in electronic packaging

Thermal management of integrated circuit chip is an increasing important challenge faced today. Heat dissipation of the chip is generally achieved through the die attach material and solders. With the temperature gradients in these materials, high thermo-mechanical stress will be developed in them, and thus they must also be mechanically strong so as to provide a good mechanical support to the chip. The use of multi-walled carbon nanotube to enhance the thermal conductivity, and the mechanical strength of die attach epoxy and Pb-free solder is demonstrated in this work

Investigation of corrosion behavior, tensile and cyclic fracture mechanism of EH36 steel welded joints

This work systematically revealed the static-dynamic corrosion failure behavior of EH36 joints under air, simulated seawater and cathodic protection in seawater. The result indicated that the seawater environment affected tensile performance slightly but acted a critical role in the fatigue behavior. Specifically, the corrosion pit and cyclic stress would respectively induce high-stress concentration and corrosion current density, significantly decreasing the fatigue strength of joints. The application of cathodic protection on joints in seawater would decrease the tensile behavior, but would continuously provide electrons for the surface and crack tip to prevent corrosion damage, improving fatigue performance of EH36 joints

Effects of different scanning patterns on nickel alloy-directed energy deposition based on thermal analysis

A novel and comprehensive evaluation index considering various processing parameters in additive manufacturing with four different scanning patterns was proposed. The relationship between the evaluation index and the performance of parts made by directed energy deposition was established and verified by experiments. The differences of thermal evolution between four scanning patterns were analysed. Comprehensive evaluation indices corresponding to different scanning patterns were calculated by integrating the contributions of various parameters, such as delamination, warping, porosity, heat accumulation, cooling rate, dendrite spacing, and deposition efficiency. The comprehensive evaluation indices off our scanning patterns were ranked in the following order (from lowest to highest): single-track zigzag, single-track, bi-direction, and spiral inward patterns. The performance of the single-track zigzag pattern was the best, and that of the spiral inward pattern was the worst. The single-track and bi-direction patterns showed intermediate performances under the same conditions. The closer the index is to zero, the better the performance. This index can be used for the quantitative evaluation of process quality and prediction of performance. It provides guidance for additive manufacturing process development and optimisation, reduces workload, and provides a new idea for quantitative performance evaluation and prediction of parts fabricated by additive manufacturing

Applications of multi-walled carbon nanotube in electronic packaging

Thermal management of integrated circuit chip is an increasing important challenge faced today. Heat dissipation of the chip is generally achieved through the die attach material and solders. With the temperature gradients in these materials, high thermo-mechanical stress will be developed in them, and thus they must also be mechanically strong so as to provide a good mechanical support to the chip. The use of multi-walled carbon nanotube to enhance the thermal conductivity, and the mechanical strength of die attach epoxy and Pb-free solder is demonstrated in this work.Published versio

Fusion boundary evolution, precipitation behaviour, and interaction with dislocations in an Fe–22Cr–15Ni steel weldment during long-term creep

A tungsten inert gas welded joint between a novel heat-resistant austenitic steel and ERNiCrCoMo-1 weld metal was investigated before and after creep in this study. The evolution of the microstructures in the base and weld metals was discussed based on the electron back-scatter diffraction (EBSD) and transmission electron microscopy (TEM) analyses. The preferred orientations of the fusion boundary after creep revealed the influence of the applied stress on creep deformation mechanism. A cooperative nucleation process of M23C6 carbides in the base metal was proposed. The finely distributed Cu-rich phase was cut off by the dislocations during creep, leading to increased mean size and reduced amount of the nano-Cu phase. A modified triple-precipitate hardening model was constructed based on TEM observations of the interactions between the particles and the dislocations in the base metal after creep at 200 MPa. The evolution of a μ phase in the weld metal involved epitaxial growth and dissolving into the matrix. Keywords: Heat-resistant steel weldment, Creep, EBSD, Nucleation mechanism, Nano Cu-rich phas

Additive manufacturing of high-performance 15-5PH stainless steel matrix composites

The consolidation of ceramic particles into the metallic matrix is promising to translate their exceptional properties from the micro-scale to the macro world. Herein, four different 15-5PH stainless steel (SS) matrix composites: 15-5PH/TiB2, 15-5PH/TiN, 15-5PH/TiC and 15-5PH/WC were fabricated by directed energy deposition (DED). The introduction of TiB2 particles substantially refines the martensite grain size, however, fails to achieve the performance improvement due to the elemental segregation of Cr and formation of considerable macro- and micro-cracks. The TiN composite realises a simultaneous enhancement of strength and ductility due to grain refinement, however, fails to enhance the corrosion resistance due to the Cr element segregation. The WC and TiC composites achieve the balance between the improved strength and ductility coupled with simultaneous enhancement of corrosion resistance. This work demonstrates the substantial potential in developing martensitic SS matrix composites with excellent strength-ductility synergy and corrosion resistance

Grain refinement of laser-arc hybrid welded 2219 aluminum alloy by introducing TiB2 particles employing laser pre-cladding

Laser-arc hybrid welding of 2219 aluminum alloy was carried out employing TiB2 particles. By pre-cladding a wide layer, the particles were easy to arrive weld edge, promoting the columnar grains neighboring the fusion line transferred to equiaxed, and the average grain size was reduced by about 50%

Effect of Ni-coated carbon nanotubes on interfacial reaction and shear strength of Sn-Ag-Cu solder joints

In this study, varying weight percentages of Ni-coated carbon nanotubes (Ni-CNTs) were incorporated into Sn-Ag-Cu (SAC) solder matrix, to form composite solder. Up to 0.05% of Ni-CNTs were successfully incorporated. The interfacial microstructure and shear strength of solders on Ni/Au-finished Cu substrates were investigated after aging at 150°C for up to 42 days. Results revealed that, after soldering and aging for various lengths of time, the interfacial intermetallic compound (IMC) thickness of the unreinforced solder joint was observed to grow more significantly than that of the composite solder joints. Furthermore, the composite solder joints also showed lower diffusion coefficients (2.5 × 10−15 cm2/s to 3.2 × 10−15 cm2/s) compared with that of the SAC solder joints (4.9 × 10−15 cm2/s). Shear test results revealed that as-soldered and aged composite solder joints had better ultimate shear strength than their monolithic counterparts and the shear strength of all aged solder joints decreased with increasing aging time