Search results

Today a large variety of printed circuit board (PCB) base materials exists on the market and new ones are added frequently. The base material suppliers, having good original equipment manufacturer (OEM) marketing, usually present the materials in an early development stage to the end customers. The customers, on the other hand, expect from their PCB suppliers that the materials are fully characterized and that qualification samples are available immediately. In many cases, the process recommendations given to the PCB manufacturers are very generic (“like FR4”), insufficient, or not practicable (“8 hours baking time”). However, optimized processing ensures the reliability of the finished PCBs, starting from general leadfree compatibility to CAF testing. This demonstrates the importance of thoroughly verified process parameters and of very specific process recommendations to minimize the number of costly and time‐consuming iterations, and to be able to meet the goal of submitting qualification samples and functional PCBs in minimum time. The purpose of this paper is to show the minimum required PCB processing recommendations, and why these have to be fixed by the material supplier before commercialization of a new base material.

The paper examines the base material suppliers' situation, customer expectations and reality and the PCB manufacturers' expectations.

The paper gives the reasons and consequences of early base material marketing.

The paper analyses today's PCB base materials market and shows the reasons and consequences of early base material marketing. Also, the minimum requirements by PCB fabricators concerning processing recommendations are given.

Examines the fourteenth published year of the ITCRR. Runs the whole gamut of textile innovation, research and testing, some of which investigates hitherto untouched aspects. Subjects discussed include cotton fabric processing, asbestos substitutes, textile adjuncts to cardiovascular surgery, wet textile processes, hand evaluation, nanotechnology, thermoplastic composites, robotic ironing, protective clothing (agricultural and industrial), ecological aspects of fibre properties – to name but a few! There would appear to be no limit to the future potential for textile applications.

Transient response of continuous composite material (CCM) fin made of high thermally conductive composite material is presented. The continuously varying effective properties of composite material such as thermal conductivity, heat capacity and density have been modelled using the Mori-Tanaka homogenization theory and rule of mixture. Additionally, temperature dependency of thermal conductivity, heat generation (composite materials) and convection coefficient (fluid properties) have also been incorporated. Different base boundary conditions are addressed such as oscillating heat flow, oscillating temperature, step-changing heat flow and step-changing temperature. At the other boundary, the fin is assumed to have a convective tip.

Lattice Boltzmann method is implemented using an in-house source code for obtaining the numerical solution of typical non-linear heat balance equation of the aforementioned problem under various transient base boundary conditions.

The effects of various thermal parameters such as material diffusivity ratio and conductivity ratio, area ratio and Biot number on transient response of fin and temperature distribution of fins are studied and interpreted. The heat transfer rate and time for attainment of steady state temperature of metal matrix composite (MMC) fin are found to be proportionally dependent on their diffusivity ratio. Additionally for higher values of area ratio and biot number, MMC fins are reported to dissipate the heat more efficiently in comparision to homogeneous fins in terms of time required to attain the steady state and surface temperature.

Response of transient fin associated with advanced class of material can facilitates the practicing engineers for designing high-performance and/or miniaturized thermal management devices as used in electronic packaging industries.

Studies of composite fin consisting of laminating second layer of material over the first layer have been reported previously, however transient response of CCM fin fabricated by continuously varying the volume fraction of two materials along the fin length has not been reported till date. Such material finds its application in thermal management and electronic packaging industries. Results are plotted in form of a graph for different application-wise material combinations that have not been reported earlier, and it can be treated as design data.

Examines the thirteenth published year of the ITCRR. Runs the whole gamut of textile innovation, research and testing, some of which investigates hitherto untouched aspects. Subjects discussed include cotton fabric processing, asbestos substitutes, textile adjuncts to cardiovascular surgery, wet textile processes, hand evaluation, nanotechnology, thermoplastic composites, robotic ironing, protective clothing (agricultural and industrial), ecological aspects of fibre properties – to name but a few! There would appear to be no limit to the future potential for textile applications.

The optimal material microstructures in pure material design are no longer efficient or optimal when accounting macroscopic structure performance with specific boundary conditions. Therefore, it is important to provide a novel multiscale topology optimization framework to tailor the topology of structure and the material to achieve specific applications. In comparison with porous materials, composites consisting of two or more phase materials are more attractive and advantageous from the perspective of engineering application. This paper aims to provide a novel concurrent topological design of structures and microscopic materials for thermal conductivity involving multi-material topology optimization (material distribution) at the lower scale.

In this work, the effective thermal conductivity properties of microscopic three or more phase materials are obtained via homogenization theory, which serves as a bridge of the macrostructure and the periodic material microstructures. The optimization problem, including the topological design of macrostructures and inverse homogenization of microscopic materials, are solved by bi-directional evolutionary structure optimization method.

As a result, the presented framework shows high stability during the optimization process and requires little iterations for convergence. A number of interesting and valid macrostructures and material microstructures are obtained in terms of optimal thermal conductive path, which verify the effectiveness of the proposed mutliscale topology optimization method. Numerical examples adequately consider effects of initial guesses of the representative unit cell and of the volume constraints of adopted base materials at the microscopic scale on the final design. The resultant structures at both the scales with clear and distinctive boundary between different phases, making the manufacturing straightforward.

This paper presents a novel multiscale concurrent topology optimization method for structures and the underlying multi-phase materials for thermal conductivity. The authors have carried out the concurrent multi-phase topology optimization for both 2D and 3D cases, which makes this work distinguished from existing references. In addition, some interesting and efficient multi-phase material microstructures and macrostructures have been obtained in terms of optimal thermal conductive path.

Currently, the most widely used Printed Circuit Board (PCB) base material is the glass reinforced epoxy known as FR‐4. To improve the electrical or the thermomechanical performance of PCBs, there are two possibilities from a material standpoint: a modification or change of the resin system and a change of the reinforcement. Currently, there are a number of resins used for high performance PCB base materials. These resin systems offer higher Tgs and lower z‐axis‐expansions for improved through hole reliability. Non‐halogenated epoxy resin systems are offered for the production of green PCBs. In addition to new resins, new reinforcements are available for use in PCBs. Which can improve the electrical parameters of the base material and the x and y axis‐ thermal expansion also changes with the use of those reinforcements. This paper compares the thermomechanical and electrical parameters of some new high performance and green base materials with the glass reinforced epoxy materials commonly used in both high layer count boards and microvia applications.

To explore the economical and reasonable semi-rigid permeable base layer ratio, solve the problems caused by rainwater washing over the pavement base layer on the slope, improve its drainage function, improve the water stability and service life of the roadbed pavement and promote the application of semi-rigid permeable base layer materials in the construction of asphalt pavement in cold regions.

In this study, three semi-rigid base course materials were designed, the mechanical strength and drainage properties were tested and the effect and correlation of air voids on their performance indexes were analyzed.

It was found that increasing the cement content increased the strength but reduced the air voids and water permeability coefficient. The permeability performance of the sandless material was superior to the dense; the performance of the two sandless materials was basically the same when the cement content was 7%. Overall, the skeleton void (sand-containing) type gradation between the sandless and dense types is more suitable as permeable semi-rigid base material; its gradation is relatively continuous, with cement content? 4.5%, strength? 1.5 MPa, water permeability coefficient? 0.8 cm/s and voids of 18–20%.

The study of permeable semi-rigid base material with large air voids could help to solve the problems of water damage and freeze-thaw damage of the base layer of asphalt pavements in cold regions and ensure the comfort and durability of asphalt pavements while having good economic and social benefits.

The purpose of this paper is to present a mask‐image‐projection‐based stereolithography (MIP‐SL) process that can combine two base materials with various concentrations and structures to produce a solid object with desired material characteristics. Stereolithography is an additive manufacturing process in which liquid photopolymer resin is cross‐linked and converted to solid. The fabrication of digital material requires frequent resin changes during the building process. The process presented in this paper attempts to address the related challenges in achieving such fabrication capability.

A two‐channel system design is presented for the multi‐material MIP‐SL process. In such a design, a coated thick film and linear motions in two axes are used to reduce the separation force of a cured layer. The material cleaning approach to thoroughly remove resin residue on built surfaces is presented for the developed process. Based on a developed testbed, experimental studies were conducted to verify the effectiveness of the presented process on digital material fabrication.

The proposed two‐channel system can reduce the separation force of a cured layer by an order of magnitude in the bottom‐up projection system. The developed two‐stage cleaning approach can effectively remove resin residue on built surfaces. Several multi‐material designs have been fabricated to highlight the capability of the developed MIP‐SL process.

A proof‐of‐concept testbed has been developed. Its building speed and accuracy can be further improved. The tests were limited to the same type of liquid resins. In addition, the removal of trapped air is a challenge in the presented process.

This paper presents a novel and a pioneering approach towards digital material fabrication based on the stereolithography process. This research contributes to the additive manufacturing development by significantly expanding the selection of base materials in fabricating solid objects with desired material characteristics.

Examines the fifthteenth published year of the ITCRR. Runs the whole gamut of textile innovation, research and testing, some of which investigates hitherto untouched aspects. Subjects discussed include cotton fabric processing, asbestos substitutes, textile adjuncts to cardiovascular surgery, wet textile processes, hand evaluation, nanotechnology, thermoplastic composites, robotic ironing, protective clothing (agricultural and industrial), ecological aspects of fibre properties – to name but a few! There would appear to be no limit to the future potential for textile applications.

Whole building life cycle assessment (WBLCA) is a key methodology to reduce the environmental impacts in the building sector. Research studies usually face challenges in presenting comprehensive LCA results due to the complexity of assessments at the building level. There is a dearth of methods for the systematic evaluation and optimization of the WBLCA performance at the design stage. The study aims to develop a design optimization framework based on the proposed WBLCA method to evaluate and improve the environmental performance at the building level.

The WBLCA development method is proposed with detailed processes based on the EN 15978 standard. The environmental product declaration (EPD) methods were adopted to ensure the WBLCA is comprehensive and reliable. Building information modeling (BIM) was used to ensure the building materials and assembly contributions are accurate and provide dynamic material updates for the design optimization framework. Furthermore, the interactive BIM-LCA calculation processes were demonstrated for measuring the environmental impacts of design upgrades. The TOPSIS-based LCA results normalization was selected to conduct the comparisons of various building design upgrades.

The case study conducted for a residential building showed that the material embodied impacts and the operational energy use impacts are the two critical factors that contribute 60–90% of the total environmental impacts and resource uses. Concrete and wood are the main material types accounting for an average of 65% of the material embodied impacts. The air and water heating for the house are the main energy factors, as these account for over 80% of the operational energy use. Based on the original WBLCA results, two scenarios were established to improve building performance through the design optimization framework.

The LCA results show that the two upgraded building designs create an average of 5% reduction compared with the original building design and improving the thermal performance of the house with more insulation materials does not always reduce the WBLCA results. The proposed WBLCA method can be used to compare the building-level environmental performances with the similar building types. The proposed framework can be used to support building designers to effectively improve the WBLCA performance.