Reliability of passivated copper multichip module structures embedded in polyimide

Multichip module (MCM) structures were used to study the reliability of copper conductors embedded in polyimide. Conductor lines fully encased in titanium passivation, 50-100 nm thick, increased in resistance less than 0.4% after 1000 h of exposure to 85% humidity at 85°C and 10-V bias. The fully encased lines also had corrosion rates six times lower than lines that had only 60% passivation coverage. Transmission lines passivated with 50 nm of titanium showed very little degradation in the rise time or amplitude of digital pulses that had a 0.5-GHz clock rate and 149-ps rise time. Copper/polyimide via chain structures were fabricated from vias having dimensions of 10-25 μm. After 1000 cycles of thermal shock from -65 to 150°C, via chains showed no significant resistance change