To provide a wiring substrate which can prevent short circuit between connection terminals, and which realizes reduction of the pitch between the connection terminals. The wiring substrate of the present invention includes a layered structure including one or more insulation layers and one or more conductor layers, and the wiring substrate is characterized in that a plurality of connection terminals are formed on the layered structure so as to be separated from one another; a filling member is filled between the connection terminals; and each of the connection terminals has a side surface composed of a contact surface which is in contact with the filling member, and a spaced surface which is not in contact with the filling member and which is located above the contact surface and below the top surface of the filling member.

A solder composition contains: a flux composition containing an (A) rosin resin, a (B) activator, a (C) thixotropic agent, and a (D) solvent; and (E) solder powder, in which the (B) component contains a (B1) dicarboxylic acid having 3 to 8 carbon atoms, the (C) component contains at least one selected from the group consisting of a (C1) amide thixotropic agent having a hydroxy group in one molecule and a (C2) glycerol thixotropic agent having a hydroxy group in one molecule, and the solder composition satisfies a condition represented by Numerical Formula (F1) below provided that a total of contents of the (C1) component and the (C2) component is defined as X and a content of the (B1) component is defined as Y,
X/2Y5X(F1).