Circuit board and mounting structure

A circuit board comprising:

• an insulating substrate;
• and
• an electrically conductive section formed on the insulating substrate, to which a chip component is electrically to be connected;
• wherein
• the insulating substrate comprises a base material having a fiber bundle composed of a plurality of single fibers, and a resin portion for covering the base material,
• the single fiber comprises a resin material which is smaller in linear expansion coefficient than a material used for the chip component,
• the resin portion is made of a resin material which is larger in linear expansion coefficient than the material used for the chip component,
• the base material is composed of a fabric cloth formed by weaving the single fibers or the fiber bundles together, and
• the fiber bundle is formed in such a manner that a cross-sectional profile of the fiber bundle sectioned along a virtual plane perpendicular to its longitudinal direction is in a horizontally long, flat shape,
• wherein a linear expansion coefficient in the longitudinal direction of the single fiber falls in a range of −10 ppm/° C. or above and 0 ppm/° C. or below (25° C. or above and 200° C. or below) and the linear expansion coefficient of the resin portion falls in a range of 10 ppm/° C. or above and 60 ppm/° C. or below (25° C. or above and 200° C. or below).