Wiring board and method for manufacturing the same

A method for manufacturing a wiring board, the method comprising:

• forming a through-hole by perforating a prepreg, which is covered with protective films, from an outer side of one of the protective films;
• filling the through-hole with a via paste;
• forming protruding portions, which are the via paste partially protruding from the through-hole, by removing the protective films after filling the through-hole with the via paste;
• disposing copper foils each including a roughened surface having skewness Rsk of 0 or less of a roughness curve defined by ISO 4287-1997 on surfaces of the prepreg so as to cover the protruding portions with the roughened surface;
• compression-bonding the copper foils onto the surfaces of the prepreg after disposing the copper foils on the surfaces of the prepreg;
• heating the copper foils, the prepreg, and the via paste while the copper foils are compression-bonded onto the surfaces of the prepreg;
• and
• patterning the copper foils to form wirings,
• wherein the via paste includes a plurality of copper particles, a plurality of tin-bismuth solder particles, and a thermally curable resin,
• a weight ratio of composition, which is copper:tin:bismuth falls in a quadrilateral defined with vertices of A (0.37:0.567:0.063), B (0.22:0.3276:0.4524), C (0.79:0.09:0.12), and D (0.89:0.10:0.01) in a ternary plot,
• a link of the plurality of copper particles is formed, and a plane-to-plane contact portion is formed between part of the copper particles and the copper foil, by compression-bonding the copper foils onto the surfaces of the prepreg, and
• a first metal region including the link;
• a second metal region including, as a main component, at least one of tin, a tin-copper alloy, and a tin-copper intermetallic compound, and formed between a surface of the link and the roughened surface;
• and a third metal region including bismuth as a main component are formed, by heating the copper foils, the prepreg, and the via paste at a temperature equal to or higher than a eutectic temperature of the solder particles for melting the solder particles.