Multilayered ceramic wiring circuit board and the method of producing the same

A method of producing a multilayered ceramic wiring circuit board including a plurality of ceramic insulating substrate layers laminated integrally, conductor layers with predetermined patterns supported on the respective ceramic insulating substrate layers and via hole conductors provided at predetermined positions of the respective ceramic insulating substrate layers for interconnecting the respective conductor layers with predetermined patterns to form a predetermined wiring circuit, the conductor layers and the via hole conductors being made of either tungsten or molybdenum, characterized in that said ceramic insulating substrate layers are produced by:

• mixing more than 70 wt% of mullite powder having an average particle size of 5 .mu.m, 10-30 wt% of silicon dioxide powder having an average particle size below 2 .mu.m, less than 15 wt% of aluminum oxide powder having an average particle size below 1 .mu.m and less than 1 wt% of metal oxide powder of at least one compound selected from the group consisting of alkali metal oxide and alkaline earth metal oxide;
• pressing and forming the mixture;
• forming via holes in the pressed and formed mixture;
• filling said via holes with a conductive paste;
• forming conductor layers on the pressed and formed mixture;
• firing the pressed and formed mixture at a temperature above where the firing shrinkage ratio thereof becomes constant simultaneously with said conductor layers and said via hole conductors,
• whereby said ceramic insulating substrate layers thus produced consist essentially of crystals of mullite, sillimanite, andalusite and kyanite;
• non-crystalline silicon dioxide occupying the interstices between the crystals and at least one compound selected from the group consisting of alkali metal oxide and alkaline earth metal oxide dissolved substantially in the crystals in solid solution and have a thermal expansion coefficient of 40-60.times.10.sup.-7 /.degree.C. and a dielectric constant below 6.7.

A method of producing a multilayered ceramic wiring circuit board comprising:

• forming a mixture of more than 70 wt% of mullite powder, 10-30 wt% of silicon dioxide powder, less than 15 wt% of aluminum oxide powder and less than 1 wt% of metal oxide powder;
• adding a resin to said mixture;
• adding a plastisizing agent to said mixture;
• blending the mixture, resin and plastisizing agent to form a slurry;
• forming the blended mixture into a plurality of green sheets;
• forming via holes in said green sheets;
• filling the via holes with a conductive paste;
• printing a predetermined circuit onto said green sheets;
• stacking a plurality of said green sheets, such that via holes on individual green sheets are aligned with via holes on other green sheets;
• and
• firing the stacked assembly at a temperature above the temperature at which the firing shrinkage ratio becomes constant.