High density thin film circuit board and method of production thereof

A high density thin film circuit board, comprising:

• a base substrate having a cavity inbetween a first and a second surface correspondingly forming a first surface hole and a second surface hole thereon, said first and second surface holes being provided for electrical conduction between said first and second surfaces, a plurality of diameters of said cavity being gradually enlarged as they are further away from said first surface and further approaching said second surface;
• at least one thin film circuit layer formed on said first surface of said substrate;
• and
• a conductor layer disposed in a lowermost layer of the at least one thin film circuit layer to be in contact with said first surface of the base substrate, said conductor layer being exposed to said first surface hole;
• wherein an inner surface of the hole is provided with one of an Ni-plated layer serving as a barrier against a diffusion of solder and an Au-plated layer for improving the wettability to solder.