Abstract: A wiring board with a stiffener includes a wiring board, a mounting region located on an upper surface of the wiring board, and a stiffener located on the upper surface of the wiring board to surround the mounting region and including a first surface facing the wiring board and a second surface located opposite to the first surface. The wiring board has a first thermal expansion coefficient. The stiffener includes a first region facing the wiring board, including the first surface, and a second thermal expansion coefficient, and a second region located on a surface side opposite to the first region, including the second surface, and has a third thermal expansion coefficient. An absolute value of a difference between the first and second thermal expansion coefficients is smaller than an absolute value of a difference between the first thermal expansion coefficient and the third thermal expansion coefficient.

Abstract: A wiring board includes a first insulation layer comprising first and second surfaces; a second insulation layer located at an outermost layer on the first surface; a third insulation layer located at an outermost layer on the second surface; a first mounting region located on an outermost surface on the first surface; a second mounting region located on the outermost surface on the first surface and surrounding the first mounting region; a plane conductor located on the third insulation layer; and a solder resist covering the third insulation layer and the plane conductor and having an opening that exposes part of the plane conductor. In plane perspective, in a frame-shaped region between outer peripheral edges of the first and second mounting regions, the plane conductor comprises clearances at point-symmetric positions taking a center of the opening as a point of symmetry.