A Thick Film Hybrid IC Amplifier for Industrial Use

Abstract

Electronic circuits for industrial uses must satisfy the following requirements: low sensitivity to changes in the surrounding temperature, high reliability, and small size. In the amplifier for a pressure transmitter described here, the temperature dependences of its properties, Zero point and Span, are intensively influenced by TCRs of the resistors used, and by a mismatching of the temperature dependences of the off-set voltages between the two operational amplifier IC chips. As forthe thick film resistors, it has been cleared that the DuPont 1700 series resistor pastes are the most suitable:TCRs of less than +80 ppm/°C can be attained, and the change in resistance of the overglazed and laser trimmed resistors is less than +0.1% after 5000 hours at 200°C. As for the operational amplifier IC chips, their temperature dependences of the off-set voltages are checked individually, utilizing a ceramic carrier containing an operational amplifier IC chip. Then a pair of ceramic carriers, with a minimum mismatching of their temperature dependences, is mounted on a thick film circuit substrate by a Pb/Sn solder reflowing. The various transistor chips are divided into three functional blocks, and bonded into three ceramic carriers. Utilization of ceramic carriers in all active devices employed results in sufficient standardization in the characterization of the semiconductor devices and in the hybridizing process.In the thick film hybrid IC amplifier for a pressure transmitter thus developed, the temperature dependences of Zero point and Span are less than –0.5% FS/100°C, respectively. The drifts of Zero point and Span are less than ±0.1% FS in the period of 3000 hours of an operating test with DC 24 V loading at 100°C.