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.
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