Ngk Spark Plug Company, Limited

Katsuhiko Hasegawa

Satoshi Hirano

Kozo Yamasaki

Naoki Kito

Osamu Hisada

Yutaro Kameyama

A multilayer-wiring substrate having a via hole structure and method for fabricating the same. Referring to FIGS. ( ) and ( ), after a via-hole is formed by exposure and development in lithography or by laser-drilling, a bottom portion of the via-hole is subjected to resin-etching so as to expose a surface A of a lower conductor as shown in FIG. ( ). The exposed surface A of the lower conductor is chemically etched so that the conductor is undercut. As a result, undesired material B such as adhered residual resin shown in FIG. ( ) is completely removed. In etching the conductor at the bottom of the via hole , the lower conductor is preferably etched in an amount of 5-30% of the thickness of the lower conductor to form a depression or recess A at a via hole bottom C as shown in FIG. ( ), thereby reliably establishing electrical continuity between the lower conductor and the upper conductor by means of a via-hole conductor as shown in FIG. ( ).

Multilayer-wiring substrate and method for fabricating same

A method of making a printed board is provided. The printed board has a base provided with a plurality of through via conductors having through holes extending completely between upper and lower surfaces of the base and closed by resin fillings and a plurality of blind via conductors having depressions closed by resin fillings. The method comprises the steps of preparing the base provided with the through via conductors having the through holes and the blind via conductors having the depressions, filling the through holes of the through via conductors and the depressions of the blind via conductors with resin paste by printing, while at the same time forming, on an upper surface of the base and at locations around the through holes of the through via conductors and the depressions of the blind via conductors, a plurality of projections made of the above described resin paste by printing, and curing the resin paste, thereby forming the resin fillings in the through holes of the through via conductors and the depressions of the blind via conductors. By this method, the upper surfaces of the resin fillings in the through holes and the depressions are not caused to recede or sink and become lower in level than the upper surface of the base but can be maintained higher in level than the upper surface of the base, thus making it possible to dispense with a manufacturing step for closing receding spaces and manufacture the printed board at lower cost.

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Aichi, Japan

Katsuhiko Hasegawa