Multilayer wiring substrate

A multilayer wiring substrate including conductive layers and insulating layers alternately stacked on each other, each of the conductive layers having a conductive pattern, a semiconductor device being mounted on a top surface of the multilayer wiring substrate, the multilayer wiring substrate comprising:

• a protective film that covers the conductive pattern of a first conductive layer of the conductive layers, the first conductive layer being a topmost layer of the conductive layers, at least one cavity being formed in the protective film to expose part of the conductive pattern of the first conductive layer, the at least one cavity being elongated in one direction;
• at least one first via-conductor that extends downward from the conductive pattern of the first conductive layer at least until the conductive pattern of a second conductive layer of the conductive layers, the second conductive layer being a second layer;
• and
• a plurality of second via-conductors that extend downward from the conductive pattern of the second conductive layer or a third conductive layer of the conductive layers, the third conductive layer being a third layer, at least until the conductive pattern of a conductive layer of the conductive layers one below the second conductive layer or the third conductive layer, wherein
• when one of a longitudinal direction of the at least one cavity and a direction perpendicular to the longitudinal direction and parallel with the top surface of the multilayer wiring substrate is defined as a first direction,
• as viewed from above,
• the at least one first via-conductor and the at least one cavity partially overlap each other,
• at least two of the plurality of second via-conductors are disposed separately from the at least one cavity so as to sandwich the at least one cavity therebetween in the first direction,
• among the second via-conductors sandwiching the at least one cavity therebetween in the first direction, a smallest gap between the at least one cavity and at least one second via-conductor disposed at one side of the at least one cavity is defined as a first smallest gap, a smallest gap between the at least one cavity and at least one second via-conductor disposed at an other side of the at least one cavity is defined as a second smallest gap, a smallest gap between the at least one cavity and the second via-conductors is defined as an overall smallest gap, and a difference between the first smallest gap and the second smallest gap is smaller than the overall smallest gap.