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This paper is a critical comparison of the currently used methods to test prepregs which do not describe to a sufficient extent the flow behaviour of a prepreg resin during the pressing process. The new test method introduced herein is a characterisation of the viscosity of the resin melt. International standardisation of this test method is recommended.

Differential Scanning Calorimetry (DSC) is an ideal technique for characterising polymeric materials such as the epoxy resin in epoxy glass prepregs and laminates, the technique having evolved from the older qualitative method of Differential Thermal Analysis (DTA). In DSC the heat flow to or from the sample is measured as a function of temperature or time. Epoxy glass prepregs are used as the bonding/insulating layer in multilayer printed circuit boards. When a sample of the epoxy resin in prepreg is heated, the heat flow that results from the exothermic curing reaction is measured and used to calculate the enthalpy ΔH of the reaction. ΔH is related to the degree of B stage curing and the flow achievable in the laminating press. Methods are given for calculating ΔH and the differences found in two manufacturers' prepreg material are discussed. The effect of ageing on ΔH, which has been found to decrease with time and with the extent of cure, is examined at room temperature and under refrigeration. The difference in the ageing properties of the two prepregs is explained by reference to a plot of the degree of conversion with time. This plot also enables the curing time required in the lamination press and the shelf life of the prepreg at room temperature to be calculated. Monitoring the degree of cure of laminates and cured prepreg using the glass transition temperature of the resin is examined. Insufficient cure may lead to problems of resin smear in multilayer printed circuit boards. Thermochemical analysis is used as a routine quality control method in the Microcircuit Assembly Techniques Facility at Marconi Research Centre for testing incoming prepreg and laminates used in multilayer printed circuit board manufacture.

To meet higher requirements on multilayer PCBs, good control of the prepreg parameters is essential. The standard prepreg tests of gel time and flow are insufficient. New test methods such as melt viscosity, scaled flow test and differential scanning calorimetry give the required information. The test methods are compared for different materials. Rheology testing using a melt viscosimeter is an important tool for both prepreg and PCB manufacturers.

In this paper, continuous glass tow preg-reinforced acrylonitrile butadiene styrene (ABS) composites were fabricated by using a 3D printing method, and the purpose of this study is the investigation of the fiber preimpregnation effect on the mechanical behavior of these composites. In addition, a simple theoretical approach (mixture law), which considers the elastic behavior of reinforced composites and a numerical simulation method based on finite element method (FEM), was used to predict the tensile stress–strain behavior of ABS/glass tow preg composites in the elastic region.

Different groups of preimpregnated glass tows with various ABS amounts (named 2%, 10%, 20% and 30%) were prepared by the solution impregnation method. Then, preimpregnated glass tows (prepregs or tow-pregs) were fed into the printer head along with the polymeric ABS filament to print the composites. The tensile, flexural and short beam tests were conducted to evaluate the mechanical properties of the printed composites.

The first result of using tow-pregs instead of dry tows in continuous fiber 3D printing is much easier printing, printability improvement and the possibility of printing layers with low thickness, which can further increase the mechanical properties. The mechanical test results showed all of the glass prepregs improve strength and modulus in the tensile, three-point bending and short beam tests compared with neat ABS specimens, but statistical analysis showed that ABS weight percentage in the prepregs had no significant effect on the mechanical strength of composites except for the tensile modulus. Samples containing 2%-prepreg (minimum ABS amount in the tow-pregs) showed a significant improvement in tensile modulus. In the simulation section, good agreement is obtained between the model predictions and experimental tensile results. The results show that an acceptable deviation (14%) exists between the experimental and predicted value of elastic modulus by the numerical model.

To the best of the authors’ knowledge, this is the first study showing the effects of ABS weight percentage in prepregs on the mechanical properties of 3D printed continuous fiber-reinforced composites and predicting the mechanical behavior of 3D printed composites by numerical simulation method.

This paper aims to show a resin-flowing model based on Darcy’s law to display the flowing properties of prepreg during lamination. The conformity between the model and experimental results demonstrates that it can provide a guideline on print circuit board (PCB) lamination.

Based on the theoretical derivations of Darcy’s law, this paper made an analysis on the flow of prepreg in the pressing process, according to which a theoretical model, namely, resin-flowing model was further formulated.

This paper establishes a resin-flowing model, according to which two experiment-verified conclusions can be drawn: first, the resin-flowing properties of material A and B can be improved when the heating rate is between 1.5 and 2.5 min/°C; second, increased pressure gradient can add the amount of flowing resin, mainly featured by increasing pressure and reducing filled thickness of prepreg.

This model provides guidance on setting lamination parameters for most kinds of prepregs and decreasing starvation risk for PCB production.

Continuously increasing requirements drive multilayer manufacturers to search for advanced manufacturing technologies and to evaluate new materials. This paper provides an insight into new multilayer bonding methods, improvements offered by laminators, and why to select high performance materials for special applications.

The purpose of this paper is to develop the multi-objective optimization approach and its numerical implementation to synthesise the model-base control for the part curing at autoclave processing, which supplies the stability and uniformity of the structure and mechanical properties of the material within the cured composite part.

The approach includes conversion of the cured part and mold geometry from their computer-aided design (CAD) to computer-aided engineering (CAE) representation, a finite element (FE) formulation of the coupled forward heat transfer/thermal kinetic problem with the parameters of prepreg, which should be determined by the thermal analysis, and, finally, a mapping of the area of 4D design space (thermal control parameters) to 2D objective space, whose coordinates are the maximum deviations of degree of cure and temperature within the cured part calculated at each call of the FE model.

The present modeling and optimization approach to the cure process control of the prepreg with thermosetting resin, as well as the means of visualizing optimization results, allow providing insight into complex curing phenomena, estimating the best achievable quality indicators of manufactured composite parts, finding satisfactory parameters of the control law and deciding considering all manufacturing constraints.

The research can be effectively used to optimize the cure process control for a wide class of polymeric composite parts, even with a complex geometry, but it requires the exact conversion of the geometry of the modeled part from the CAD to CAE environment, which implies the need for excluding all topological imperfections of original CAD model to eliminate the possible formation of void elements and other reasons that do not allow the correct FE meshing. Because thermal, rheological and kinetics parameters, which include the governing equations of cure process, depend on the reinforcing fibers, and especially on the resin properties, the thermal testing for the new modeled prepreg needs to be performed.

Computer implementation of the proposed approach and numerical method for model-based optimal control synthesis for composite part cure process can be used in aircraft, rotorcraft, ship and automotive technologies at the design of manufacturing process of the large composite parts with complex shape.

This will allow much better quality for large-scale composite parts, excluding very expensive, time-, energy- and material-consuming multiple cure process testing.

This is first time the problem of optimal control synthesis for curing the large-scale composite parts of complex shape was solved.

A new treatment method for the copper innerlayers of polyimide multilayer printed wiring boards has been developed. Conventional oxide coatings experience acid penetration through the bonding interface during through‐hole plating pretreatment. This problem was eliminated by substitution of metallic copper for the surface oxide. Promotion of the copper innerlayer adhesion to the prepreg by the oxide coating was based upon a mechanical interlocking effect caused by the minute roughness of the oxide crystals. Reduction treatment of the surface oxide layer was found to give a metallic copper surface with no changes in its morphology. Adhesion strength of polyimide prepregs to copper foils after the reduction treatment was equivalent to that of the original brown oxide coating. Acid resistance was enhanced by elimination of the oxide layer from the bonding interface. The reduction treatment, combined with the conventional oxide coating technique, can realise high density multilayer printed wiring boards with greater reliability and performance.

Rigid multilayer polyimide printed wiring boards exhibit unusually large dimensional change during the lamination process. Therefore, the use of large polyimide multilayer panels for high density circuitry is often limited. This study examined ten probable causes for dimensional instability and how each affected the shrinkage/growth in the laminated panel. The report shows that a combination of methods and materials can reduce the resultant dimensional change experienced during lamination from 0·001 inch/inch to less than 0·0002 inch/inch in planar directions.

THE applications of advanced fibre reinforced composite materials for the manufacture of lightweight stable components have rapidly expanded in the aerospace and other industries in recent years. Typically, these components are produced from woven fabrics or unidirectional tapes of carbon, aramid or glass fibre, preimpregnated with partially cured or ‘B‐staged’ epoxy resins. Layers of this ‘prepreg’ material are laid onto a mould tool to form the component which is then cured in an autoclave at temperatures around 180°C under a consolidating pressure of 1001bf/in2.