Wiring board structure

A wiring board structure, comprising:

• a substrate having a first side and a second side opposite to each other;
• a first build-up circuit layer disposed on the first side of the substrate, wherein the first build-up circuit layer has a first wiring area, and the first wiring area comprises:
• a first metal;
• a first dielectric;
• and
• a second build-up circuit layer disposed on the second side of the substrate, wherein the second build-up circuit layer has a second wiring area, and the second wiring area comprises:
• a second metal, wherein a total volume of the second metal is less than a total volume of the first metal;
• a second dielectric;
• and
• a third dielectric, wherein a material of the third dielectric is different from a material of the second dielectric, and a ratio of a total volume of the third dielectric to a total volume of the second dielectric is between 0.45 and 0.55,
• wherein a top surface and a bottom surface of the third dielectric are coplanar with a top surface and a bottom surface of the second dielectric, respectively.