The present disclosure relates to a wiring board.

Japanese Patent Application Publication 2009-74823 discloses a wiring board including a ceramic insulator layer and an electrode pad, wherein the electrode pad is disposed on a surface of the ceramic insulator layer for connection with a terminal of a probe etc., and is electrically connected to a conductor (a so-called via) extending through the ceramic insulator layer.

FIG. 4 is a schematic cross-sectional view of a conventional wiring board. As shown in FIG. 4, a ceramic insulator layer 102 includes in its surface a void V formed due to expansion and contraction of ceramic upon firing. The void V is likely to catch a residue such as: plating pretreatment liquid used for formation of wiring including an electrode pad 104; and a product of reaction between the plating pretreatment liquid and a conductor 103.

Such residue may cause a problem: in case that the electrode pad 104 is formed over the void V containing the residue, the residue would vaporize and cause a bulge in the electrode pad 104, through a heating process such as: a curing of ceramic layers stacked with the ceramic insulator layer 102; and a blazing or soldering of components to the wiring board.

The bulge may cause insufficient electrical connection between the electrode pad 104 and the conductor 103, wherein the conductor 103 extends through the ceramic insulator layer 102. In other words, the bulge may reduce reliability of connection involving the electrode pad 104.