Designing to safe power limits in hybrid circuits

Experiments were performed at two heat-transfer conditions, simulating minimum and maximum heat transfer. Since hybrid-circuit heat dissipation is dependent on factors such as heat sinking, package design, substrate material, environment and other considerations, it was decided to bracket the extremes of power dissipation for these circuits. Tests performed at these two heat-transfer conditions yielded data which were used to formulate relationships among the hybrid variables of temperature, size, and power. To establish these relationships, the various sizes of resistors and hybrid substrates were accommodated by using the ratio of resistor to substrate size to relate the power density and temperature. Both resistor and substrate temperature were predictable within the desired temperature limits of 0 to 300°C using the relationships developed. The power-temperature relationships developed make possible the predictions of both resistor and substrate temperatures during circuit design, which is both necessary and advantageous for the design of hybrid circuits having increased power and circuit density