Production of silica "green" tape and co-fired silica substrates therefrom

A process for preparing a silica tape which comprises:

• providing a silica powder in the form of substantially spherical particles having a diameter ranging from about 0.1 to about 2 microns, said silica powder obtained by reaction of an alkyl silicate in aqueous alcoholic solution in the presence of ammonium hydroxide,
• mixing said silica powder with an aqueous medium containing an organosol, to form a slurry of said silica particles,
• casting said slurry on a support, and
• drying said slurry to form a silica tape on said support.

A process for preparing a silica tape which comprises:

• providing an amorphous silica powder of substantially uniform size spherical particles having a diameter ranging from about 0.1 to about 2 microns, said silica powder obtained by reaction of a tetraalkyl orthosilicate in aqueous alcoholic solution in the presence of ammonium hydroxide,
• mixing said silica powder with an aqueous medium containing an organosol comprising a vinyl acetate-acrylic copolymer emulsion as binder, the molecular weight of said copolymer ranging from about 2,000 to about 10,000, the amount of said binder employed ranging from about 15 to about 35%, by weight of said silica powder, said aqueous medium also containing polyethylene glycol as plasticizer, said polyethylene glycol having a molecular weight ranging from about 4,000 to about 6,000, the amount of said polyethylene glycol employed ranging from about 1% to about 5%, by weight of said binder, to form a slurry of said silica particles in said aqueous medium,
• casting said slurry on a polyester film, employing a doctor blade, and
• drying said slurry at elevated temperature not exceeding about 60.degree. C., to form a silica tape on said polyester film.

A process for producing a multilayer circuit board which comprises:

• 14,
• cutting said silica tape on said polyester film into a plurality of tapes on said polyester film,
• punching via and alignment holes into each of said plurality of tapes on said polyester film,
• screening a predetermined pattern of gold or copper circuit metalization on each of said plurality of tapes, and filling said via holes with said metallization,
• removing said plurality of tapes from their respective polyester films,
• forming a plurality of said tapes into a registered stack of layers,
• laminating the registered stack of silica tape layers, and
• co-firing at about 1050.degree. C. the laminated stack of layers of silica and circuit metalization to form a monolithic multilayer circuit board having a low dielectric constant and exhibiting substantially the same dimensional changes in X and Y directions after co-firing.