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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: Steven Lu (steven.lu@baesystems.com )
Organization:BAE Systems
Date posted: Mon Oct 7 17:18:56 US/Eastern 2002
Subject: Pressure Sensor MTBF
Message:
I'm working on MTBF prediction on a pressure sensor that the vendor didn't have test data to support reliability prediction. The pressure sensor is a piezoresistive pressure sensor chip attached to a ceramic substrate. The sensor has four thick film resistors laser trimed on ceramic forming a Wheatston bridge. Any help on how to calculate MTBF will be very appreciated.


Reply:

Subject: Thick Film Sensor Wheatstone Bridge
Reply Posted by: B.W.Dudley (bdudley@iitri.org )
Organization: RAC
Date Posted: Tue Oct 8 14:25:19 US/Eastern 2002
Message:
I searched the web for information and found numerous sources for a description on how they work and block diagrams of the designs. Most wheatstone sensors have four resistor elements connected to a power source and a signal path. Reliability data was not found, so I searched for failure information on thick film resistor operation. Telcordia has a reliability model for thick and thin film resistors used as networks. Taking this information with a connector model for a transistor socket to simulate the three pin connection phase, I used the MIL-HDBK-217 model to complete the analysis. The results look like this for a ground benign condition: Thick Film [Telcordia Model] -- 0.5 failures per billion hours x 4 resistors = 2.0 failures per billion hours Connection [MIL-HDBK-217] -- 5.1 failures per billion hours Quality factor for commercial / industrial component -- 3 Total for the pressure sensor is [(0.5 x 4) + 5.1] x 3 = 21.7 failures per billion hours Thank you for calling the Reliability Analysis Center.


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