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Some high voltage dc breakdown properties of thick film circuits on alumina

Dybwad, G.L.

This report describes high voltage dc breakdown tests on various PtAu and Au thick film hybrid microcircuits on alumina (Al{sub 2}O{sub 3}). Samples were prepared with current thick film design and manufacturing rules. The purpose was to determine the voltage margins between current design rules and typical applied voltages on real circuits. We also analyzed what happened during a breakdown event. We used a versatile computer-controlled test set to obtain breakdown data. This showed that design conductors 10 mil wide with equal design spaces on alumina and coated with a fired protective glaze (DuPont 9137) had the highest breakdown values (2700 Vdc). Bare design circuits and Au conductor crossover features had a lower breakdown value (1400 to 1600 Vdc). Both these values are well above logic circuit applied voltages ({le}50v). This may account for the excellent field performance obtained to date. Ambient humidity changes to 43% R.H. and voltage rise rates between 3 and 2300 V/sec had little influence on breakdown values ({le}200 Vdc). Voltage breakdown values were little influenced by our two geometries: point-to-line samples which simulated corners and long parallel line samples. Breakdown behaved like a spark in air rather than an arc. Breakdown in glaze went through it to air rather than along the glaze/alumina interface. The spark was found to be similar to lightning in that it consisted of a string of current pulses lasting a total of 1 to 2 seconds. Spark locations were from surface asperities or defects near but not at the point of minimum optically measured separation. Hence, we found that circuits made using current design rules for hybrid microcircuit manufacture are adequate or conservative as regards safe margins against logic voltage dc breakdown to the extent studied here. 13 refs., 19 figs.