High-temperature storage and thermal cycling studies of Heraeus-Cermalloy thick film and Dale power wirewound resistors

In this work, the high temperature testing of power wirewound and thick film resistors is reported. The resistance values of the Dale power wirewound resistors tested were 1 Ω, 100 Ω, and 10 kΩ with rated power levels of 5 W and 25 W. Stability with long term storage (10000 hrs) at 300°C has been measured for the wirewound resistors unpowered and powered at 20% of rated power. The Dale resistors have also completed 1000 thermal cycles with a temperature range from -55°C to 225°C. Additionally TCR measurements were performed on these resistors. Three 900 Series thick film resistor pastes from Heraeus-Cermalloy were studied: 100 Ω/□, 1 KΩ/□, 10 KΩ/□. The temperature coefficient of resistance (TCR) was measured from 27°C to 500°C in 50°C increments. A 2×2 matrix of variables was included in the 300°C storage test: untrimmed resistors, resistors trimmed up 50% in value, unpowered, and powered at 1/8 W. Palladium/Silver was the initial termination choice for these 300°C studies, but silver migration quickly became a problem. Gold terminated Heraeus-Cermalloy resistors were manufactured and have completed over 4500 hours of storage at 300°C