In recent years, with the development trends towards lighter, shorter and smaller high performance and high reliability electronic products, printed circuit boards have…
Abstract
In recent years, with the development trends towards lighter, shorter and smaller high performance and high reliability electronic products, printed circuit boards have ceaselessly been growing in terms of higher density and layer count. At present, conventional FR‐4 laminate, which is reinforced by glass fabric, has become the universal purpose base material because of its excellent adhesion, good electrical insulation and mechanical properties. However, with its relatively low glass transition temperature (Tg) of approximately 135°C, large coefficient of thermal expansion in the z‐axis direction, poor thermal resistance and propensity for resin smear while drilling, normal FR‐4 is severely limited in high performance applications, especially for multilayer board fabrication, and is used only for multilayer boards with layer counts below ten. Furthermore, conventional FR‐4 is usually cured using dicyandiamide, which could potentially cause insulation deterioration of the printed circuit boards and vulnerability in terms of delamination under high temperature treatment. These effects could degrade the reliability of PCBs and therefore, base material suppliers have focused on improving the Tg and thermal resistance to broaden the operating window of conventional FR‐4.
Details
Keywords
Runyao Yu, Xingwang Bai, Xueqi Yu and Haiou Zhang
A new wire arc additive manufacturing (WAAM) process combined with gravity-driven powder feeding was developed to fabricate components of tungsten carbide (WC)-reinforced iron…
Abstract
Purpose
A new wire arc additive manufacturing (WAAM) process combined with gravity-driven powder feeding was developed to fabricate components of tungsten carbide (WC)-reinforced iron matrix composites. The purpose of this study was to investigate the particle transportation mechanism during deposition and determine the effects of WC particle size on the microstructure and properties of the so-fabricated component.
Design/methodology/approach
Thin-walled samples were deposited by the new WAAM using two WC particles of different sizes. A series of in-depth investigations were conducted to reveal the differences in the macro morphology, microstructure, tensile performance and wear properties.
Findings
The results showed that inward convection and gravity were the main factors affecting WC transportation in the molten pool. Large WC particles have higher ability than small particles to penetrate into the molten pool and survive severe dissolution. Small WC particles were more likely to be completely dissolved around the top surface, forming a thicker region of reticulate (Fe, W)6C. Large WC particles can slow down the inward convection more, thereby leading to an increase in width and a decrease in the layer height of the weld bead. The mechanical properties and wear resistance significantly increased owing to reinforcement. Comparatively, samples with large WC particles showed inferior tensile properties owing to their higher susceptibility to cracks.
Originality/value
Fabricating metal matrix composites through the WAAM process is a novel concept that still requires further investigation. Apart from the self-designed gravity-driven powder feeding, the unique aspects of this study also include the revelation of the particle transportation mechanism of WC particles during deposition.