A new embeddable copper oxide based thin film resistor material

With the best tolerance and thermal stability among the commercially available embeddable resistor products, thin film resistors having copper foil as carrier have been expected to be one of the most potential candidates for meeting the future HDI development trend of PCB manufacturing process. However, before the potential can be realized, the problem of too small sheet resistivity - 250Ω/□ max limited by the native low resistivity of alloy resistive materials to cover the major usage range 10000 Ω/□ needs to be solved beforehand. In this study, a new composite thin film material comprising both the dispersed palladium metal conductor phase made from metal-organic deposition (MOD) of palladium acetate precursor, and the continuous semiconductor phase made of copper oxide got from 3 different processes - SILAR (Successive Ionic Layer Absorption and Reaction), MOD of copper acetate precursor and direct oxidation of copper foil has been developed and verified successfully with performance of broad sheet resistivity coverage from 1000 to 10000 Ω/□ and low temperature coefficient of resistance TCR ≪ ±200 ppm/°C. Due to different conductive mechanisms of the two different phase materials, the electric properties of the newly developed thin film resistive material can be easily adjusted. Increasing the metal conductor phase content - Pd with nature of low resistivity and positive TCR will make the resistance smaller and shift TCR positively and vice versa. In addition, for the copper oxide semiconductor phase materials with nature of high resistivity and negative TCR, cupric oxide CuO is superior to cuprous oxide Cu2O for its better compatibility with existing alkaline etching process.