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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum (src_forum@alionscience.com )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Original Message:

Posted by: Keith Heinzig (keith@solustech.com )
Organization:Solus Micro Tech.
Date posted: Mon Jan 28 19:58:04 US/Eastern 2002
Subject: NTC Thermistor Reliability
Message:
I am trying to locate reliability data on NTC thermistors running above 70 degrees C for extended periods. If anyone could point me to a source of data I would appreciate it.


Reply:

Subject: NTC Thermistor Reliability
Reply Posted by: Bruce Dudley (bdudley@alionscience.com )
Organization: Reliability Analysis Center
Date Posted: Wed Jan 30 15:59:09 US/Eastern 2002
Message:
NTC Thermistors are composed of metal oxides and the fabrication uses basic ceramic technology today as it has for decades. The NTC device is the negative temperature coefficient of resistance. When using negative temperature coefficient devices, a point can be reached where the self-heating current causes a resistance drop resulting in more self-heating that increases to the destruction of the device. This is thermal runaway. This is not a problem with positive temperature coefficient devices. Long-term reliability studies indicate that extended operation or continued cycling above 90 degrees C may cause thermistors to eventually exceed tolerance limits. Many vendors, including Microtech, have NTC devices that are qualified to operate from 25 to 85 degrees C. The new PRISM reliability program has a thermistor model with failure data and the results for continuously operated device at 70 degrees C is 0.043 failure per million hours.


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