Multilayer printed wiring board and its production process, resin composition for filling through-hole

A multilayer printed wiring board having a multilayer core board and build-up wiring layers formed on both surfaces of the multilayer core board,

• said multilayer coreboard comprising:
• a core material;
• at least one innerlayer conductor circuit formed on the core material;
• at least one interlaminar resin insulating layer covering the at least one innerlayer conductor circuit;
• at least one via-hole formed in the at least one interlaminar resin insulating layer so as to electrically connect the innerlayer conductor circuit;
• and
• at least one through-hole formed in the at least one interlaminar resin insulating layer and the core material to pass therethrough, the through-hole being filled with filler comprising particulate substance having an average particle size ranging 0.1 to 30 μm, resin and ultrafine inorganic powder having an average particle size ranging from 1 to 1000 nm;
• said build-up wiring layer comprising:
• at least one interlaminar resin insulating layer and at least one outerlayer conductor circuit alternately laminated on the multilayer core board;
• and
• at least one via hole formed in the at least one interlaminar resin insulating layer so as to electrically connect the at least one outerlayer conductor circuit;
• at least one via-hole in the build-up wiring layer being located just above the at least one through-hole and directly connected to the at least one through-hole.