A method of forming the wiring board. The wiring board includes a first substrate, and a second substrate having a smaller mounting area than a mounting area of the first substrate. A base substrate is laminated between the first substrate and the second substrate such that the first substrate extends beyond an edge of the second substrate, and at least one via formed in at least one of the first substrate or the second substrate. A thickness of a portion of the base substrate that is sandwiched between the first substrate and the second substrate is greater than a thickness of a portion of the base substrate that is not sandwiched between the first substrate and the second substrate.