PURPOSE: To obtain a high-density and multilayer circuit board by using a thick-film and thin-film hybrid substrate and by making the maximum value of signal wiring length in thin film smaller than that of signal wiring length in thin-film.
CONSTITUTION: When wiring becomes thinner, conductor resistance becomes higher and signal is attenuated according to exp[-R.l/2 Z0] and does not exceed the threshold. Z0 is characteristics impedance, R is resistance, and l is wiring length. Wiring length of wiring substrate is generally short. Also, generally in precision wiring made by optic processing, wiring resistance becomes relatively large as compared with thick-film resistance. For example, although resistance of a copper wiring with a width of 20μm and a thickness of 2μm is 5ohms/cm or more, resistance of W wire with a width of 100μm and a thickness of 10μm is 1ohms/cm or less and wiring can be made only as much as 1/5 the length of thick-film. W thick-film wirings 2 and 3, thin-film insulation layer 4, and a copper thin-film wiring 5 are piled up on an alumina ceramics 1, allowable amount of signal attenuation is determined, high integration by a thin-film and low-resistance wiring by a thick-film can be made to allow a high-density multi-layer substrate to be formed while retaining transmission characteristics.
MURATA AKIRA
ISHI ICHIRO
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