PRISM Forum - Message Replies

Topic: PRISM Questions and Answers
Topic Posted by: SRC ( )
Organization: SRC
Date Posted: Wed Jan 12 8:33:33 US/Eastern 2000
Topic Description: Welcome to the PRISM forum! Please feel free to post your questions and comments about the PRISM assessment software here.

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Original Message:

Posted by: Thomas Urbanczyk ( )
Organization:Systema Engineering
Date posted: Thu Nov 4 9:52:14 US/Eastern 2004
Subject: How to calculate failure rates for PCBs
Is it possible to model PCBs in PRISM? What method would you suggest to model PCBs in PRISM? In other prediction tools like Isograph Workbench (MIL-HDBK-217F) it is possible to use a "Interconnetion Assembly" to take thermal interaction between components and PCB into account. Best regards Thomas Urbanczyk


Subject: Calculating failure rates of PCB's
Reply Posted by: David Dylis ( )
Organization: Reliability Analysis Center
Date Posted: Thu Nov 4 13:59:14 US/Eastern 2004
The RAC PRISM methodology includes a database of field failure rates for varying types of components. This database includes failure rates for a “circuit card, unpopulated” in varying environments. One option would be to select the appropriate failure rate for the circuit card from this database. Since solder joint failures are already addressed within the PRISM component models only components on the circuit card that are defined either using the PRISM database or by a “user defined” failure rate would have to have a solder joint failure rate assigned.

Another alternative is to calculate the failure rate using MIL-HDBK-217 and insert the calculated value into the PRISM analysis as a “user defined failure rate”. If this is alternative is selected, the MIL-HDBK-217 failure rate would have to be adjusted to account for any period of non-operation as PRISM failure rates are based on calendar hours and not operational hours.

If you have any additional questions, feel free to contact me.

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