SRC Forum - Message Replies
Forum: Reliability & Maintainability Questions and Answers
Topic: Reliability & Maintainability Questions and AnswersTopic Posted by: Reliability & Maintainability Forum (firstname.lastname@example.org )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998
Posted by: IC
Subject: PRISM vs. commercially available prediction tools...
New electronic Component Models based on over 10^12 hours of field experience data
Most commercially available prediction tools on the market use MIL-HDBK-217 as their basis for prediction methodology. The latest update to MIL-HDBK-217 occurred in 1995 and does not account for technological improvements that have occurred beyond 1995. The models in PRISM, released in 2001, are new prediction models based on current field data collected by RAC. As an example, the update for the MIL-HDBK-217 microcircuit model last occurred in 1992 and the data that went into the development of these models was based on parts manufactured in 1991 or before (with the bulk of the data being from the 1980’s). One of the major complaints of MIL-HDBK-217 was the failure rates that it predicted for PEMs. The quality of ICs manufactured within the last 10+ years has improved exponentially. Also, it was a disputed fact that MIL-HDBK-217 was overly pessimistic in predicting the failure rates of PEMs, even when it was current. RAC data has shown (see RAC Order code: PEM2, page 84) little difference between the failure rates of PEM and hermetic integrated circuits when properly used.
In addition, process-related variability is a major influence to the overall reliability of a system. This variability had not been adequately addressed in previous prediction methodologies. RAC data has shown that parts may only comprise 22% of the overall system failure rate. PRISM accounts for the process related variability of an assembly or system failure rate through a process grading methodology. By answering a series of questions, the user establishes a scoring profile whose total value is translated into a quantitative factor that impacts the predicted failure rate. Process grade types currently defined within PRISM are: Design, Manufacturing, Part Quality, System Management, Can-Not –Duplicate (CND), Induced, Wearout, Growth and Infant Mortality. Grading is accomplished by assessing the processes in a self audit-like fashion. Any or all of these process grade types can be assessed and graded. If the user chooses not to address a specific process grade, the model simply reverts to the default “average” value. If the user chooses to apply the grading methodology for any process grade, there is a minimum number of questions that must be assessed and graded. Beyond this minimum, the user can selectively assess and grade additional criteria. If answers to the grading questions are not known, the model simply ignores that criteria.
PRISM also accounts for the complete usage profile for a system including dormant/non-operating conditions that were previously ignored by other prediction technologies.
A demonstration version of the PRISM assessment software is available for download at the following web site: http://rac.alionscience.com/prism/Prism_Demo.html. This demo allows a user to review the RAC PRISM prior to purchase and contains information representative of the actual data contained in the full version. Some features such as save and print will not function, and the demo does not contain the RAC Electronic Part Reliability Database (EPRD) and Nonelectronic Part Reliability Database (NPRD) data. The tool contains an example system and built-in help to address specifics about the tool.
Reliability tools developed by commercial software vendors are integrating PRISM into their products. For instance, RELEX includes a PRISM module that will allow a user to perform a PRISM predictions within RELEX. ReliaSoft’s BlockSim and Raytheon’s ASENT programs also work directly with the PRISM software. In addition, other reliability software vendors are in the process of integrating the PRISM standard into their software suites.
If you have any additional questions, feel free to contact me.
D. David Dylis