Method of fabricating an improved multi-layer ceramic substrate

Claim 1

An improved method of fabricating a monolithic sintered MLC substrate for a semiconductor package comprising forming a plurality of first ceramic green sheets of a thickness in the range of 6-9 mils, forming vias in said first sheets filling said vias and imprinting metallurgy redistribution patterns with a conductive metallurgy paste on said first sheets, forming a plurality of second ceramic green sheets, forming vias and imprinting metallurgy patterns with a conductive metallurgy paste on said second sheets, forming a single top ceramic green sheet of ceramic material of a thickness of at least 20% greater than the individual thickness of said first sheets, forming a via pattern in said top sheet wherein at least some vias have a center to center spacing when fired in the range of 7-12 mils, with the via diameter being in the range of 35 to 55% of said center to center via spacing, filling said vias in said top sheet with a conductive metallurgy paste, said metallurgy paste, when sintered, and the said ceramic material of said top sheet when sintered having a differential coefficient of expansion of at least 0.8×10 -6 /°C., assembling said second sheets, in underlying relation to said first sheets, and said top sheet in overlying relation to said first sheets, sintering the resultant assembly to form a monolithic ceramic substrate having an internal conductive metallurgy system, the thickness relationship between said first sheets and said top sheet minimizing via to via cracking in said monolithic substrate.