Multilayer ceramic circuit boards with copper conductors

The application of copper (Cu) to multilayer ceramic circuit boards fabricated by the green-sheet method is studied. The glass-ceramic composite composed of borosilicate (B₂O₃ -SiO₂) glass and alumina (Al₂O₃) densifies below the melting point of Cu. The major technical difficulty is to fire the circuit board without Cu oxidation and carbon residue. Carbon intermixes with the glass matrix, lowering the fired density, flexural strength, and breakdown voltage. However, less than 100 p.p.m. of carbon does not influence these properties. A 30-layer ceramic circuit board with a carbon concentration of less than 30 p.p.m. has been fabricated. The signal propagation delay time is 7.3 ns/m. The sheet resistivity of Cu conductors is 1.2 mΩ/□