A component assembly that can be easily built in a main substrate with high accuracy is formed such that a glass transition temperature of a built-in-component layer of an assembly substrate in which multiple capacitors are embedded is higher than a glass transition temperature of a built-in-component layer of a built-in-component substrate. Thus, thermal deformation of the component assembly is prevented when the built-in-component substrate in which the component assembly is built is heated during reflow, for example. The component assembly can thus be highly accurately built in the built-in-component substrate. Moreover, when the component assembly in which the multiple capacitors are embedded is built in the built-in-component substrate, electrode pads of the component assembly in which the multiple capacitors are embedded can be electrically connected to wiring layers of the built-in-component substrate by soldering despite the variation in height among the capacitors.