| 摘要 |
<p>A high dielectric constant (K'>/=4), low thermal coefficient of dielectric constant (TCK'</=150 ppm/ DEG C.) electrical substrate material comprises a fluoropolymer (preferably PTFE) filled with particulate ceramic material (powder) which exhibits low loss, comparatively high K' and acceptable TCK'. Examples of such ceramic powders include "class 1" capacitor ceramics. In accordance with an important feature of this invention, it has been discovered that it is insufficient to use only a low TCK' filler (e.g., class 1 capacitor ceramic powder) in the fluoropolymeric binder in order to achieve the desired TCK'. Instead, it has been discovered that the coefficient of thermal expansion (CTE) of the composite must also be sufficiently low (e.g.,</=35 ppm/ DEG C.) to result in a composite which consistently maintains a low TCK'. This low CTE is achieved by adding one or more additional particulate ceramic fillers. These additional fillers have a low CTE and are of a composition which differs from the low TCK' fillers. Examples include silica and alumina. In accordance with still another important feature of this invention, the particle size distribution of the particulate ceramic fillers are carefully controlled to achieve low porosity (e.g.,</=15% when the filler content exceeds about 50 volume %).</p> |
