2,379 research outputs found

    Mechanical and electrical characterisation of anisotropic conductive adhesive particles

    Get PDF
    This thesis presents research into the mechanical and electrical characterisation of Anisotropic Conductive Adhesive (ACA) particles and their behaviour within typical joints. A new technique has been developed for study of individual ACA particle mechanical and electrical performance when undergoing deformation. A study of the effects of planarity variations on individual electrical joints in real ACA assemblies is presented firstly, followed by the research on the mechanical deformation and electrical tests of individual ACA particles undergoing deformation. In the co-planarity research, experiments introducing deliberate rotation between a chip and substrate were designed and carried out to simulate planarity variations in ACA assemblies. There are two outputs from this part of the research. One is the planarity variation effects on individual electrical joints in ACA assemblies, and the other is the effect of bond thickness on the resistance of a real joint. [Continues.

    Additive manufacturing and joints: Design and methods

    Get PDF
    The industrialization of the Additive Manufacturing (AM) processes is enabling the use of AM components as final product in several applications. These processes are particularly relevant for manufacturing components with optimized custom-tailored geometries. However, to fully exploit the potentiality of AM, the development of knowledge aimed to produce dedicated design methods is needed. Indeed, even if AM enables the manufacturing of new kinds of structures, e.g. 3D lattice structures, it introduces process-specific design input and limitations that needs design methods different to from the ones for subtractive manufacturing. Design for AM (DfAM) is a design methodology that aims to take advantage of new buildable geometries but taking into account also AM processed materials anisotropy and 3D printing constraints. Recent literature focused on the assembly of AM components and on the AM components joining to a main structure. The conclusion was that adhesive bonding is a promising joining process, especially considering its improved stress distribution compared to fastening, but at the time of writing a method that combines DfAM and adhesive bonding knowledge is not available. The work presented in this thesis focused on developing knowledge on design for AM and bonded joints. First step was evaluating testing methods for AM and producing data on materials properties. Secondly, the early works on tailoring approaches for AM joints, published recently in scientific literature, were analyzed. Then AM dedicated designs, modifications and testing methods were proposed both for the adherends (in the thickness and on the surfaces) and the joints. Specifically, an innovative joint design concept was introduced, i.e. using the 3D printing parameters as bonded joint design factors. Eventually, feasibility of performing joints using multi-material AM with conductive polymer to embed heating elements was assessed. The 3D printed through the thickness circuits is a cutting-edge approach to enable new solutions for joints structural monitoring and self-healing

    Conductive Particles in Anisotropic Conductive Films

    Get PDF
    Anisotropic Conductive Films (ACFs) are the major products used for fine-pitch interconnection technology in electronic packaging because of their low incidence in electrical interconnection issues such as high contact resistance and open/short-circuit failure. ACF are conductive adhesives composed of a suitable binder and electrically Conductive Particles (CP). These CP can be selected from a variety of materials to meet specific applications or requirements. In this Mini Review we describe the different types of conductive particles that can be used in ACF, the advantages and disadvantages of each type, as well as other relevant issues such as particle size, concentration, and capture rate. This work could serve as a guide for any group that is interested in research on ACFs.Fil: Trupp, Federico Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física. Laboratorio de Polímeros y Materiales Compuestos; ArgentinaFil: Cibils, Roberto Manuel. Invap S. E.; ArgentinaFil: Goyanes, Silvia Nair. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin

    Mechanics of Non Planar Interfaces in Flip-Chip Interconnects

    Get PDF
    With the continued proliferation of low cost, portable consumer electronic products with greater functionality, there is increasing demand for electronic packaging that is smaller, lighter and less expensive. Flip chip is an essential enabling technology for these products. The electrical connection between the chip I/O and substrate is achieved using conductive materials, such as solder, conductive epoxy, metallurgy bump (e.g., gold) and anisotropic conductive adhesives. The interconnect regions of flip-chip packages consists of highly dissimilar materials to meet their functional requirements. The mismatches in properties, contact morphology and crystal orientation at those material interfaces make them vulnerable to failure through delamination and crack growth under various loading patterns. This study encompasses contact between deformable bodies, bonding at the asperities and fracture properties at interfaces formed by the interconnects of flip-chip packages. This is achieved through experimentation and modeling at different length scales, to be able to capture the detailed microstructural features and contact mechanics at interfaces typically found in electronic systems

    Isotropically conductive adhesive filled with silver metalised polymer spheres

    Get PDF
    Isotropic conductive adhesives (ICAs) have a growing range of applications in electronics packaging and have recently emerged as an important material in photo-voltaic module interconnections, particularly for thin-film and other non-silicon technologies where soldering processes are often unsuitable due to the nature of the metallisation or the limited maximum temperature the assembly can be exposed to. ICAs typically comprise of a high volume fraction of solid metallic flakes, usually silver, in an adhesive matrix because of its highly conductive oxide however, this thesis will focus on adhesives containing a large volume fraction of silver coated/metalised mono-sized polymer spheres (Ag-MPS). Incorporating silver coated mono-sized polymer spheres is anticipated to deliver specific advantages such as a significant reduction in the required silver content, improvement of the overall mechanical properties and flexibility to tune the properties of the filler according to the application compared with conventional flake filled adhesives. In this research advancements in the understanding of Ag-MPS filled ICAs, both through theory and experiments, have been made. Analytical models to predict an individual Ag-MPS resistance and Ag-MPS filled ICA resistance have been developed. The experiments based on the flat punch nanoindentation technique have been conducted to determine individual Ag-MPS resistances. The theoretical and experimental studies establish Ag-MPS diameter, coating resistivity, coating thickness, contact radius, and contact geometry as the main contributors towards the resistance of an Ag-MPS filled ICAs. These studies showed that Ag-MPS resistance decreases with increasing coating thickness and contact radius but increases with increasing coating resistivity. The experiments have also been conducted to investigate the effect of Ag-MPS volume fraction, diameter, coating thickness, curing conditions and shrinkage (affecting contact radius) on ICA conductivity and comparisons are made with flake filled and commercial ICAs. The results showed that ICA conductivity increases with increasing volume fraction and coating thickness but decreases with diameter. More importantly the results showed that conductivities similar to those of flake filled ICAs, including those commercially available, can be obtained using 70% less silver. The results show that, Ag content can be reduced further to just 7% with use of larger 30μm Ag-MPS but with a lower resulting conductivity. Thus for applications where very high conductivity is not required larger Ag-MPS may offer even greater potential cost benefits, which is something flake filled ICAs cannot offer. This is a significant achievement which can allow tuning of ICA formulations according to the demands of the application, which is not possible with the use of silver flakes as there is only a limited range of silver flake volume fractions that will yield useful levels of conductivity

    Novel fine pitch interconnection methods using metallised polymer spheres

    Get PDF
    There is an ongoing demand for electronics devices with more functionality while reducing size and cost, for example smart phones and tablet personal computers. This requirement has led to significantly higher integrated circuit input/output densities and therefore the need for off-chip interconnection pitch reduction. Flip-chip processes utilising anisotropic conductive adhesives anisotropic conductive films (ACAs/ACFs) have been successfully applied in liquid crystal display (LCD) interconnection for more than two decades. However the conflict between the need for a high particle density, to ensure sufficient the conductivity, without increasing the probability of short circuits has remained an issue since the initial utilization of ACAs/ACFs for interconnection. But this issue has become even more severe with the challenge of ultra-fine pitch interconnection. This thesis advances a potential solution to this challenge where the conductive particles typically used in ACAs are selectively deposited onto the connections ensuring conductivity without bridging. The research presented in this thesis work has been undertaken to advance the fundamental understanding of the mechanical characteristics of micro-sized metal coated polymer particles (MCPs) and their application in fine or ultra-fine pitch interconnections. This included use of a new technique based on an in-situ nanomechanical system within SEM which was utilised to study MCP fracture and failure when undergoing deformation. Different loading conditions were applied to both uncoated polymer particles and MCPs, and the in-situ system enables their observation throughout compression. The results showed that both the polymer particles and MCP display viscoelastic characteristics with clear strain-rate hardening behaviour, and that the rate of compression therefore influences the initiation of cracks and their propagation direction. Selective particle deposition using electrophoretic deposition (EPD) and magnetic deposition (MD) of Ni/Au-MCPs have been evaluated and a fine or ultra-fine pitch deposition has been demonstrated, followed by a subsequent assembly process. The MCPs were successfully positively charged using metal cations and this charging mechanism was analysed. A new theory has been proposed to explain the assembly mechanism of EPD of Ni/Au coated particles using this metal cation based charging method. The magnetic deposition experiments showed that sufficient magnetostatic interaction force between the magnetized particles and pads enables a highly selective dense deposition of particles. Successful bonding to form conductive interconnections with pre-deposited particles have been demonstrated using a thermocompression flip-chip bonder, which illustrates the applicable capability of EPD of MCPs for fine or ultra-fine pitch interconnection

    Mechanical and electrical characterisation of individual ACA conductor particles

    Get PDF
    Anisotropic conductive adhesives (ACAs) consist of a polymer adhesive matrix containing fine conductive particles. The primary objective of this experimental research is to establish a clearer understanding of the effects of the bonding force on the deformation of individual ACA particles and their resulting conductivity when in contact with an appropriate metallic surface. This has been achieved through simultaneous measurements of the deformation and electrical resistance whilst applying force using a specially configured nano-indenter machine, where the "indenter", instead of being pointed, had a flat tip about 20-30 mum in diameter. The merit of using this machine is that very small forces, of the order of 100 mN, can be accurately applied to the particles to a resolution of 100 nN and the resulting deformations, of less than 6 mum, can then be recorded to a resolution of 0.1 nm. The results showed that the ACA particle deformation was nonlinear and that the force/deformation at which particle crushing occurs was affected by the load rate. The resistance was observed to decrease as the deformation increased up to the crush point at which stage it increased slightly. The voltage versus current behaviour of a deformed ACA particle was also found to be linear

    3D printed sensing systems for upper extremity assessment

    Get PDF
    corecore