New mullite ceramic packages and substrates

Recent VLSI packaging technology requires high propagation speed, high wiring density and high thermal dissipation. In order to achieve these requirements, ceramic packages need to have a low thermal-expansion coefficient, a low dielectric constant, and a high thermal conductivity. For these purposes, new mullite ceramics have been developed. Their advantages and characteristics are as follows: (1) low dielectric constants (5.4 approximately 7.3 at 1 MHz), which are favorable for the high propagation speed; (2) low thermal expansion coefficients (3.0 approximately 4.5*10/sup -6// degrees C), which permit the direct attachment of a large silicon chip; (3) higher mechanical strength (20 approximately 31 kg/mm/sup 2/) than that for old mullite ceramics; (4) realization of tungsten metallization with a high adhesion strength by using Y/sub 2/O/sub 3/ as an additive; (5) low cost; and (6) ease of processing. The conventional alumina production process can be used for the new ceramic.<>