ELECTRONIC COMPONENT CONTAINED SUBSTRATE

An electronic components built-in substrate is provided to narrow a preparation pitch of a solder ball and to mount the solder balls which are necessary for electrical connection between wiring substrates, into a small space, thereby reducing the entire dimensions. An electronic components built-in substrate comprises a pair of wiring substrates(10,20), electronic components(30) which are mounted between the pair of wiring substrates, a solder ball(40) which connects the substrates electrically, and a sealing resin(80) which seals the space between the substrates. The one wiring substrate faced to the other substrate on which the electronic components are mounted, comprises a greater opening than a plane figure of the electronic components at the opposite site to the electronic components.